JOURNAL OF PHYCOLOGY, Issue 3 2008
Zhou Yang
To investigate the changes in the morphology and polysaccharide content of Microcystis aeruginosa (Kütz.) Kütz. during flagellate grazing, cultures of M. aeruginosa were exposed to grazing Ochromonas sp. for a period of 9 d under controlled laboratory conditions. M. aeruginosa responded actively to flagellate grazing and formed colonies, most of which were made up of several or dozens of cells, suggesting that flagellate grazing may be one of the biotic factors responsible for colony formation in M. aeruginosa. When colonies were formed, the cell surface ultrastructure changed, and the polysaccharide layer on the surface of the cell wall became thicker. This change indicated that synthesis and secretion of extracellular polysaccharide (EPS) of M. aeruginosa cells increased under flagellate grazing pressure. The contents of soluble extracellular polysaccharide (sEPS), bound extracellular polysaccharide (bEPS), and total polysaccharide (TPS) in colonial cells of M. aeruginosa increased significantly compared with those in single cells. This finding suggested that the increased amount of EPS on the cell surface may play a role in keeping M. aeruginosa cells together to form colonies. [source]

Forest Stand Dynamics and Livestock Grazing in Historical Context

CONSERVATION BIOLOGY, Issue 5 2005
MICHAEL M. BORMAN
clima; incendio forestal; pastoreo histórico; pino ponderosa; supresión de fuego Abstract:,Livestock grazing has been implicated as a cause of the unhealthy condition of ponderosa pine forest stands in the western United States. An evaluation of livestock grazing impacts on natural resources requires an understanding of the context in which grazing occurred. Context should include timing of grazing, duration of grazing, intensity of grazing, and species of grazing animal. Historical context, when and under what circumstances grazing occurred, is also an important consideration. Many of the dense ponderosa pine forests and less-than-desirable forest health conditions of today originated in the early 1900s. Contributing to that condition was a convergence of fire, climate, and grazing factors that were unique to that time. During that time period, substantially fewer low-intensity ground fires (those that thinned dense stands of younger trees) were the result of reduced fine fuels (grazing), a substantial reduction in fires initiated by Native Americans, and effective fire-suppression programs. Especially favorable climate years for tree reproduction occurred during the early 1900s. Exceptionally heavy, unregulated, unmanaged grazing by very large numbers of horses, cattle, and sheep during the late nineteenth and early twentieth centuries occurred in most of the U.S. West and beginning earlier in portions of the Southwest. Today, livestock numbers on public lands are substantially lower than they were during this time and grazing is generally managed. Grazing then and grazing now are not the same. Resumen:,El pastoreo de ganado ha sido implicado como una causa de la mala salud de los bosques de pino ponderosa en el occidente de Estados Unidos. La evaluación de los impactos del pastoreo sobre los recursos naturales requiere de conocimiento del contexto en que ocurrió el pastoreo. El contexto debe incluir al período de ocurrencia, la duración y la intensidad del pastoreo, así como la especie de animal que pastoreó. El contexto histórico, cuando y bajo que circunstancias ocurrió el pastoreo, también es una consideración importante. Muchos de los bosques densos de pino ponderosa y de las condiciones, menos que deseables, de salud de los bosques actuales se originaron al principio del siglo pasado. Contribuyó a esa condición una convergencia de factores, fuego, clima y pastoreo, que fueron únicos en ese tiempo. Durante ese período, hubo sustancialmente menos incendios superficiales de baja intensidad (que afectaron a grupos densos de árboles más jóvenes) como resultado de la reducción de combustibles finos (pastoreo), una reducción sustancial en los incendios iniciados por Americanos Nativos y programas efectivos de supresión de incendios. Al inicio del siglo pasado hubo años con clima especialmente favorable para la reproducción de árboles. Al final del siglo diecinueve y comienzo del veinte hubo pastoreo no regulado ni manejado, excepcionalmente intensivo, por una gran cantidad de caballos, reses y ovejas en la mayor parte del oeste de E.U.A. y aun antes en porciones del suroeste. En la actualidad, el número de semovientes en terrenos públicos es sustancialmente menor al de ese tiempo, y el pastoreo generalmente es manejado. El pastoreo entonces y el pastoreo ahora no son lo mismo. [source]

A Quantitative Conservation Approach for the Endangered Butterfly Maculinea alcon

CONSERVATION BIOLOGY, Issue 2 2004
MICHIEL F. WallisDeVries
The quality and size of habitat patches and their isolation from other patches are the main parameters for an assessment of population persistence, but translating persistence probabilities into practical measures is still a weak link in conservation management. I provide a quantitative conservation approach for the endangered myrmecophilous butterfly Maculinea alcon in the Netherlands. All 127 colonies known on heathland since 1990 were investigated for patch quality, size, and isolation. I assessed habitat quality in three 10 × 10 m plots for most colonies. Site occupancy in 1998,1999 was only 56%. Occupancy was best explained by a logistic regression including patch area, host ant presence, host plant abundance, overall heathland area, and connectivity between sites ( R2= 0.410, p < 0.0001); it correctly classified the occupied or vacant status for 82% of the sites. Connectivity contributed only 3.6% to the total explained variation of site occupancy, indicating that habitat characteristics were more important than isolation in determining population persistence at the examined scale level (>500 m). Grazing and sod cutting had a beneficial impact, but in combination these practices proved detrimental. Hydrological measures to prevent drainage were also associated with lowered occupancy. I used the different components in the logistic regression to formulate objective management recommendations. These consisted of sod cutting, reduction of management intensity, enlargement of habitat, or combinations of these recommendations. The results highlight the importance of careful management when site quality is determined by multiple factors. The quantitative conservation approach followed here can be fruitfully extended to other endangered species, provided enough is known about their ecological requirements and how management actions affect them. Resumen:,La preservación de fragmentos individuales es extremadamente importante para especies en peligro con capacidad de dispersión limitada. La calidad y tamaño de los fragmentos de hábitat y su aislamiento de otros fragmentos son los parámetros principales para la evaluación de la persistencia de la población, pero la traducción de probabilidades de persistencia en medidas prácticas aun es un eslabón débil en la gestión de conservación. Proporciono un método cuantitativo de conservación para la mariposa mirmecófila Maculinea alcon en peligro en Holanda. Se investigó a las 127 colonias conocidas en brezales desde 1990 para calidad, tamaño y aislamiento del fragmento. Evalué la calidad del hábitat en tres parcelas de 10 × 10 m en la mayoría de las colonias. La ocupación de sitios en 1998-1999 fue sólo 56%. La ocupación fue mejor explicada por regresión logística incluyendo la superficie del fragmento, presencia de hormigas huésped, abundancia de plantas huésped, superficie total del brezal y conectividad entre sitios ( R2= 0.410, p < 0.0001); clasificó el estatus de ocupado o vacante en 82% de los sitios. La conectividad contribuyó con solo 36% de la variación total de sitio de ocupación, lo que indica que las características de hábitat fueron más importantes que el aislamiento en la determinación de la persistencia de la población en el nivel de escala examinado (>500 m). El pastoreo y el corte de pasto tuvieron un impacto benéfico pero combinadas, estas prácticas fueron perjudiciales. Obras hidrológicas para prevenir la desecación también se asociaron con una disminución en la ocupación. Utilicé los diferentes componentes de la regresión logística para formular recomendaciones objetivas de gestión. Estas incluyeron el corte de pasto, reducción en la intensidad de manejo, aumento de hábitat o combinaciones de estas recomendaciones. Los resultados resaltan la importancia de la gestión cuidadosa cuando la calidad del sitio está determinada por múltiples factores. El método cuantitativo de preservación utilizado puede ser extendido exitosamente a otras especies en peligro, siempre que sean suficientemente conocidos sus requerimientos ecológicos y la forma en que le afectan las acciones de manejo. [source]

Local Gradients of Cowbird Abundance and Parasitism Relative to Livestock Grazing in a Western Landscape

CONSERVATION BIOLOGY, Issue 6 2000
Christopher B. Goguen
We predicted that both cowbird abundance and parasitism rates of vireo nests would decrease with increasing distance from active livestock grazing, and that the nesting success of vireos would increase. We measured cowbird abundance and host density and located and monitored vireo nests in pinyon-juniper and mixed-conifer habitats that ranged from actively grazed to isolated from livestock grazing by up to 12 km. Cowbird abundance declined with distance from active livestock grazing and was not related to host density or habitat type. Brood parasitism levels of vireo nests (n = 182) decreased from> 80% in actively grazed habitats to 33% in habitats that were 8,12 km from active grazing but did not vary by habitat type or distance to forest edge. Vireo nesting success was higher in mixed-conifer habitat than in pinyon-juniper but was unrelated to distance from active livestock grazing. Nest losses due to parasitism declined with distance from active livestock grazing. Our results suggest that cowbird abundance and parasitism rates of hosts may be distributed as a declining gradient based on distance from cowbird feeding sites and that isolation from feeding sites can reduce the effects of parasitism on host populations. These findings provide support for management techniques that propose to reduce local cowbird numbers and parasitism levels by manipulating the distribution of cowbird feeding sites. The presence of parasitized nests> 8 km from active livestock grazing suggests that, in some regions, management efforts may need to occur at larger scales than previously realized. Resumen: Estudiamos patrones locales de abundancia del tordo cabeza café (Molothrus ater), las tasas de parasitismo y el éxito de nidada de un hospedero común, el vireo (Vireo plumbeus), en relación con la distribución del pastoreo en una región poco desarrollada del noreste de Nuevo México, entre 1992 y 1997. Pronosticamos que tanto la abundancia del tordo, como las tasas de parasitismo de nidos de vireo disminuirían con un incremento en la distancia a las zonas de pastoreo activo de ganado y el éxito de nidada de vireos incrementaría. Medimos la abundancia de tordos y la densidad de hospederos y localizamos y monitoreamos los nidos de vireos en hábitats de pino-cedro y de coníferas mixtas que variaron desde activamente pastoreadas hasta sitios distanciados del pastoreo hasta por 12 km. La abundancia de los tordos disminuyó con la distancia de las zonas de pastoreo activo de ganado y no estuvo relacionada con la densidad de hospederos o el tipo de hábitat. Los niveles de parasitismo de las nidadas del vireo (n = 182) disminuyeron de> 80% en hábitats activamente pastoreados a 33% en hábitats que estuvieron de 8 a 12 km de distancia de los sitios de pastoreo activo, pero no variaron con el tipo de hábitat ni la distancia al borde del bosque. El éxito de nidada de vireos fue mayor en el hábitat mixto de coníferas que en el hábitat de pino-cedro, pero no estuvo relacionado con la distancia al sitio de pastoreo. Las pérdidas debidas al parasitismo disminuyeron con la distancia al sitio activo de pastoreo. Nuestros resultados sugieren que la abundancia de tordos y las tasas de parasitismo de hospederos podría estar distribuida en forma de un gradiente en descenso basado en la distancia a los sitios de alimentación de los tordos y a que el aislamiento de los sitios de alimentación puede reducir los efectos del parasitismo de las poblaciones de hospederos. Estos resultados apoyan las técnicas de manejo que proponen la reducción local de números de tordos y los niveles de parasitismo al manipular la distribución de sitios de alimentación de tordos. La presencia de nidos parasitados> 8 km de sitios con pastoreo activo sugiere que, en algunas regiones, los esfuerzos de manejo deben ocurrir a escalas mayores a lo que anteriormente se pensaba. [source]

In Praise of Grazing

CURATOR THE MUSEUM JOURNAL, Issue 3 2005
Tom L. Freudenheim
First page of article [source]

Grazing and community structure as determinants of invasion success by Scotch broom in a New Zealand montane shrubland

DIVERSITY AND DISTRIBUTIONS, Issue 1 2003
P. J. Bellingham
Abstract. Scotch broom (Cytisus scoparius (L.) Link; Fabaceae) is a problematic invasive plant in many countries, and while attention has been paid to traits that make it a successful invader, there has been less focus on the properties of ecosystems that it invades. We conducted an experiment in a New Zealand montane shrubland with tussock grasses that has been invaded by Scotch broom to determine features that rendered it susceptible to invasion. We planted broom seedlings into the shrubland (control) and into three treatments: (1) resident shrubs removed, (2) tussocks removed and (3) shrubs and tussocks removed. We measured broom seedling mortality and growth over two growing seasons. The site was grazed by sheep in the first season, and scarcely grazed in the second, wetter season. Survivorship across all treatments after 19 months was 42%, and was lowest where shrubs were retained but tussocks removed. Broom seedlings grew taller and had greater leaf areas in treatments that retained shrubs. Neighbouring (within 49 cm) shrubs had no effects on survivorship or growth of broom seedlings. Neighbouring tussocks increased survivorship of broom seedlings but depressed their growth. Grazing by sheep was the most important determinant of survivorship and growth of broom seedlings, and effects were uniform regardless of experimental treatments. Initial high mortality of seedlings (48% in the first 3 months) was due to grazing, and height growth was often negative during periods of grazing. In the second growing season when the site was less grazed and there was greater rainfall, there was a rapid increase in height across all treatments. Continued grazing of the site by sheep is likely to be the chief means of retarding the invasion. [source]

Survival of Escherichia coli O157:H7 in private drinking water wells: influences of protozoan grazing and elevated copper concentrations

FEMS MICROBIOLOGY LETTERS, Issue 1 2002
Rebekka R.E Artz
Abstract The survival characteristics of Escherichia coli O157:H7 in private drinking water wells were investigated to assess the potential for human exposure. A non-toxigenic, chromosomally lux -marked strain of E. coli O157:H7 was inoculated into well water from four different sites in the North East of Scotland. These waters differed significantly in their heavy metal contents as well as nutrient and bacterial grazer concentrations. Grazing and other biological factors were studied using filtered (3 and 0.2 ,m) and autoclaved water. The survival of E. coli O157:H7 was primarily decreased by elevated copper concentrations. This hypothesis was supported by acute toxicity assay data. In addition, significant protozoan predation effects were observed in untreated water when compared with survival rates in filtered water. The combination of these two factors in particular determines the survival time of the pathogen in a private water well. It therefore appears that wells with higher water quality as assessed using the European Union Drinking Water Directive standards will also allow survival of E. coli O157:H7 for much longer periods. [source]

The balance between photosynthesis and grazing in Antarctic mixotrophic cryptophytes during summer

FRESHWATER BIOLOGY, Issue 11 2002
William Marshall
SUMMARY 1. Grazing and photosynthetic contributions to the carbon balance of planktonic, mixotrophic cryptophytes in Lakes Fryxell and Hoare in the Taylor Valley, Antarctica were measured during November and December 2000. 2. The cryptophytes never became entirely photosynthetic, although carbon derived from grazing decreased in December. Individual grazing rates ranged between 5.28 and 10.08 bacteria cell,1 day,1 in Lake Fryxell and 0.36,11.76 bacteria cell,1 day,1 in Lake Hoare. Grazing rates varied temporally and with depth in the water column. In Lake Fryxell, which is a meromictic lake, highest grazing occurred just above the chemocline. Individual photosynthetic rates ranged from 0.23 to 1.35 pg C cell,1 h,1 in Lake Fryxell and 0.074 to 1.08 pg C cell,1 h,1 in Lake Hoare. 3. Carbon acquisition by the cryptophyte community gained through grazing ranged between 8 and 31% during November in Lake Fryxell, dropping to between 2 and 24% in December. In Lake Hoare grazing contributed 12,21% of the community carbon budget in November and 1,28% in December. Around 4% of the carbon acquired from grazing and photosynthesis was remineralised through respiration. 4. Mixotrophy is probably a major survival strategy for cryptophytes in the extreme lakes of the Dry Valleys, because perennial ice-cover severely limits light penetration to the water column, whereas these phytoflagellates are not normally mixotrophic in lower latitude lakes. The evidence suggests that mixotrophy may be a mechanism for supplementing the carbon budget, as well as a means of acquiring nutrients for growth. [source]

Modelling Soil Erosion by Grazing: Recent Developments and New Approaches

GEOGRAPHICAL RESEARCH, Issue 1 2007
JOHN B. THORNES
Abstract Grazing is still widely held responsible for land degradation. The interaction between grazing and erosion is still rather poorly understood. As a consequence, counter-measures and associated management techniques have been slow to develop in southern Europe compared with Australia. Developments in ecological and economic-ecological modelling have improved our understanding of the processes and enhanced management capacity. Some of these developments are reviewed and two applications are described. One is a model for semi-extensive grazing in dry Mediterranean mountain conditions in which the shepherds, on random paths, seek to optimise resources use for economic benefit. The other is a spatial optimisation of vegetation canopy to minimise erosion rates. [source]

Structural heterogeneity and productivity of a tall fescue pasture grazed rotationally by cattle at four stocking densities

GRASSLAND SCIENCE, Issue 1 2008
Maria Silvia Cid
Abstract The spatial heterogeneity in the structure and the productivity of the vegetation was examined in a tall fescue (Festuca arundinacea Schreb.) pasture rotationally grazed at four stocking densities in the Pampean region of Argentina. The examined pasture was grazed at the stocking densities of 3.6, 4.6, 5.6 and 6.6 animals ha,1 with a two-paddock 14-day rotational grazing system. Spatial distribution of plant height was examined as well as the percentages of short patch area (heavily utilized patches) or tall patch area (areas ungrazed or lightly defoliated). In addition, biomass, growth rate and relative growth rate were assessed for both short and tall patches. Grazing generated patchiness in vegetation structure and growth at all stocking densities. Increased stocking density caused an increase in the percentage of the short patch area in the paddocks. Short patches had relatively less live biomass than tall ones, but their relative growth rate was 31% higher than that of tall patches (0.021 ± 0.007 vs 0.016 ± 0.005 g DM g DM,1 day,1). The increase in stocking density enlarged the proportion of short patch areas with higher relative growth rate. The relative growth rate (average between short and tall patches) of the two highest stocking densities was 61.7% higher than that of the low stocking density treatments (0.023 ± 0.006 vs 0.014 ± 0.004 g DM g DM,1 day,1). Although the growth rate of the short patches did not exceed the value of the tall patches, the high value of relative growth rate appeared to indicate a higher photosynthetic capacity of the short patches. Moreover, live biomass did not decrease during the experimental period even in the short patch areas showing that, in the particular conditions of our study, overgrazing did not occur at the range of the stocking density examined. [source]

Simulating daily soil water under foothills fescue grazing with the soil and water assessment tool model (Alberta, Canada)

HYDROLOGICAL PROCESSES, Issue 15 2004
Emmanuel Mapfumo
Abstract Grazing is common in the foothills fescue grasslands and may influence the seasonal soil-water patterns, which in turn determine range productivity. Hydrological modelling using the soil and water assessment tool (SWAT) is becoming widely adopted throughout North America especially for simulation of stream flow and runoff in small and large basins. Although applications of the SWAT model have been wide, little attention has been paid to the model's ability to simulate soil-water patterns in small watersheds. Thus a daily profile of soil water was simulated with SWAT using data collected from the Stavely Range Sub-station in the foothills of south-western Alberta, Canada. Three small watersheds were established using a combination of natural and artificial barriers in 1996,97. The watersheds were subjected to no grazing (control), heavy grazing (2·4 animal unit months (AUM) per hectare) or very heavy grazing (4·8 AUM ha,1). Soil-water measurements were conducted at four slope positions within each watershed (upper, middle, lower and 5 m close to the collector drain), every 2 weeks annually from 1998 to 2000 using a downhole CPN 503 neutron moisture meter. Calibration of the model was conducted using 1998 soil-water data and resulted in Nash,Sutcliffe coefficient (EF or R2) and regression coefficient of determination (r2) values of 0·77 and 0·85, respectively. Model graphical and statistical evaluation was conducted using the soil-water data collected in 1999 and 2000. During the evaluation period, soil water was simulated reasonably with an overall EF of 0·70, r2 of 0·72 and a root mean square error (RMSE) of 18·01. The model had a general tendency to overpredict soil water under relatively dry soil conditions, but to underpredict soil water under wet conditions. Sensitivity analysis indicated that absolute relative sensitivity indices of input parameters in soil-water simulation were in the following order; available water capacity > bulk density > runoff curve number > fraction of field capacity (FFCB) > saturated hydraulic conductivity. Thus these data were critical inputs to ensure reasonable simulation of soil-water patterns. Overall, the model performed satisfactorily in simulating soil-water patterns in all three watersheds with a daily time-step and indicates a great potential for monitoring soil-water resources in small watersheds. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Experimental Analysis of Grazing by the Mayfly Meridialaris chiloeensis on Different Successional Stages of Stream Periphyton

INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 3 2004
Verónica Díaz Villanueva
Abstract In this study we determined grazing effects of the South Andean endemic mayfly Meridialaris chiloeensis on periphyton at different stages of successional development. Grazing effects were studied through a two-factor experimental design (colonization stages X grazer density) in a stream-side channel in spring and winter. Our results showed an absence of proportionality between grazer density and periphyton decline in response to grazers at low and intermediate levels of periphytic biomass; however, when periphyton biomass was high a direct inverse relationship was observed between post-grazing biomass and grazer density. The relationship between periphytic algae (chlorophyll a concentration) and periphyton (total periphytic ash-free dry mass) (C/OM index) was used as an estimation of the autotrophic fraction in the total periphyton matrix. Grazing did not alter the C/OM index indicating that both autotrophic and heterotrophic fractions of the periphyton components were reduced in the same proportion. Ordination of samples using the relative abundance of diatom species showed that herbivore effect was less evident at intermediate and late stage of colonization than at early one. These results support the statement that the outcome of the herbivore-periphyton interaction may depend on the successional stage of the periphyton community. In spring Fragilaria pinnata relative abundance, on the basis of cell counts, was reduced by grazing and Nitzschia palea was enhanced. In the winter experiment, grazing decreased Achnanthes minutissima relative abundance. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

,It Takes Two Hands to Clap': How Gaddi Shepherds in the Indian Himalayas Negotiate Access to Grazing

JOURNAL OF AGRARIAN CHANGE, Issue 1 2007
RICHARD AXELBY
This article examines the effects of state intervention on the workings of informal institutions that coordinate the communal use and management of natural resources. Specifically it focuses on the case of the nomadic Gaddi shepherds and official attempts to regulate their access to grazing pastures in the Indian Himalayas. It is often predicted that the increased presence of the modern state critically undermines locally appropriate and community-based resource management arrangements. Drawing on the work of Pauline Peters and Francis Cleaver, I identify key instances of socially embedded ,common' management institutions and explain the evolution of these arrangements through dynamic interactions between individuals, communities and the agents of the state. Through describing the ,living space' of Gaddi shepherds across the annual cycle of nomadic migration with their flocks I explore the ways in which they have been able to creatively reinterpret external interventions, and suggest how contemporary arrangements for accessing pasture at different moments of the annual cycle involve complex combinations of the formal and the informal, the ,traditional' and the ,modern'. [source]

Effects of Grazing on Bituminaria bituminosa (L) Stirton: A Potential Forage Crop in Mediterranean Grasslands

JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 6 2006
M. Sternberg
Abstract Plant traits of Bituminaria bituminosa, as affected by different intensities of cattle grazing, were studied in a Mediterranean grassland in Israel. B. bituminosa is a widespread Mediterranean perennial legume species that may potentially serve as a fodder crop in Mediterranean grasslands. The aims of the present study were: (i) to evaluate the responses of B. bituminosa to different cattle grazing intensities; (ii) to study functional traits associated with grazing tolerance; and (iii) to evaluate its potential as an alternative forage crop in the region. A total of 100 B. bituminosa plants were monitored in field conditions. During the growing season each individual was sampled five times and the following plant traits were monitored each time: (i) aboveground biomass production, (ii) plant height, (iii) specific leaf area (SLA), (iv) number of flowers, (v) seed mass and size, (vi) tannin concentration in leaves, (vii) total nitrogen in leaves, (viii) fibre concentration in leaves (Neutral Detergent Fiber), and (ix) in vitro dry matter digestibility. The results showed that grazing intensity and history of grazing affected B. bituminosa performance. Plant biomass, height, and flower and seed production were all reduced when plants were exposed to cattle grazing. However, under moderate grazing intensities, its plant cover remained relatively stable indicating a potential tolerance under this stocking rate. The nutritious characteristics of B. bituminosa leaves were good, and the condensed tannins concentration found indicated favourable conditions for digestion. Moreover, the in vitro digestibility studies indicated relatively high values (46,51 %) of digestion. B. bituminosa may be considered as a potential crop for cattle feeding in Mediterranean grasslands. Growing this plant in dense stands in rotational paddocks may provide alternative sources of natural fodder protein, reducing the potential costs of artificial feed supplements. [source]

Patterns of species richness on very small islands: the plants of the Aegean archipelago

JOURNAL OF BIOGEOGRAPHY, Issue 7 2006
Maria Panitsa
Abstract Aim, To investigate the species,area relationship (SAR) of plants on very small islands, to examine the effect of other factors on species richness, and to check for a possible Small Island Effect (SIE). Location, The study used data on the floral composition of 86 very small islands (all < 0.050 km2) of the Aegean archipelago (Greece). Methods, We used standard techniques for linear and nonlinear regression in order to check several models of the SAR, and stepwise multiple regression to check for the effects of factors other than area on species richness (,habitat diversity', elevation, and distance from nearest large island), as well as the performance of the Choros model. We also checked for the SAR of certain taxonomic and ecological plant groups that are of special importance in eastern Mediterranean islands, such as halophytes, therophytes, Leguminosae and Gramineae. We used one-way anova to check for differences in richness between grazed and non-grazed islands, and we explored possible effects of nesting seabirds on the islands' flora. Results, Area explained a small percentage of total species richness variance in all cases. The linearized power model of the SAR provided the best fit for the total species list and several subgroups of species, while the semi-log model provided better fits for grazed islands, grasses and therophytes. None of the nonlinear models explained more variance. The slope of the SAR was very high, mainly due to the contribution of non-grazed islands. No significant SIE could be detected. The Choros model explained more variance than all SARs, although a large amount of variance of species richness still remained unexplained. Elevation was found to be the only important factor, other than area, to influence species richness. Habitat diversity did not seem important, although there were serious methodological problems in properly defining it, especially for plants. Grazing was an important factor influencing the flora of small islands. Grazed islands were richer than non-grazed, but the response of their species richness to area was particularly low, indicating decreased floral heterogeneity among islands. We did not detect any important effects of the presence of nesting seabird colonies. Main conclusions, Species richness on small islands may behave idiosyncratically, but this does not always lead to a typical SIE. Plants of Aegean islets conform to the classical Arrhenius model of the SAR, a result mainly due to the contribution of non-grazed islands. At the same time, the factors examined explain a small portion of total variance in species richness, indicating the possible contribution of other, non-standard factors, or even of stochastic effects. The proper definition of habitat diversity as pertaining to the taxon examined in each case is a recurrent problem in such studies. Nevertheless, the combined effect of area and a proxy for environmental heterogeneity is once again superior to area alone in explaining species richness. [source]

Impacts of traditional land uses on biodiversity outside conservation areas: effects on dung beetle communities of Vaalbos National Park

AFRICAN JOURNAL OF ECOLOGY, Issue 2 2010
Thokozani S. Simelane
Abstract Grazing is one of the key processes in terrestrial ecosystems and this can be provided by both indigenous and domestic ungulates. However, a question remains whether or not traditional forms of land use such as the grazing of domestic animals support the maintenance of biodiversity. If it does not, then the second question becomes to what extent does grazing of domestic animals alter the systems and processes that support biodiversity? This study demonstrates that in attempting to answer this question, small organisms like dung beetles are ideal indicators that can be used to express significant differences between conserved (indigenous) and non-conserved (domestic) land. As a general trend, studies that investigated these differences displayed differences through analysis of the diversity indices. This method has in most cases demonstrated a lack of contrast between conserved and non-conserved land. In the existence of such uncertainty this study has demonstrated that in such cases, where the analysis of biodiversity indices fail to demonstrate significant differences a closer examination of actual species such as guilds and functional groups could confirm significant differences between conserved and non-conserved land. These apparently conflicting findings reflect the need to consider the actual elements of biodiversity (e.g. species) when assessing conservation issues rather than just the statistical measures of biodiversity. Résumé Le pâturage est un des processus clés dans les écosystèmes terrestres, et il est le fait d'ongulés aussi bien indigènes que domestiques. Pourtant, la question subsiste de savoir si oui ou non des formes traditionnelles d'utilisation des terres telles que le pâturage des animaux domestiques favorisent le maintien de la biodiversité. Si la réponse est non, la seconde question consiste à se demander dans quelle mesure le pâturage des animaux domestiques modifie les systèmes et les processus qui sous-tendent la biodiversité. Cette étude montre que, pour essayer de répondre à cette question, de petits organismes comme les bousiers sont des indicateurs idéaux que l'on peut utiliser pour exprimer des différences significatives entre les terres protégées (animaux indigènes) et non protégées (animaux domestiques). Selon une tendance générale, les études qui ont recherché ces différences exprimaient des différences par l'analyse des indices de biodiversité. Dans la plupart des cas, cette méthode montrait un manque de contraste entre terres conservées et non conservées. Lorsqu'une telle incertitude subsiste, cette étude a pu montrer que, lorsque l'analyse des indices de biodiversité n'arrive pas à prouver de différences significatives, un examen plus approfondi d'espèces réelles, comme des guildes ou des groupes fonctionnels, peut confirmer des différences significatives entre les terres préservées et non préservées. Ces résultats apparemment contradictoires montrent bien qu'il est nécessaire de considérer les éléments réels de la biodiversité (ex. des espèces) lorsque l'on évalue des questions de conservation, au lieu de se contenter de mesures statistiques de la biodiversité. [source]

Long-term effects of prescribed early fire, grazing and selective tree cutting on seedling populations in the Sudanian savanna of Burkina Faso

AFRICAN JOURNAL OF ECOLOGY, Issue 1 2009
Didier Zida
Abstract Annual early fire, selective tree cutting and exclusion of grazing are currently used as management tools in the Sudanian savanna of Burkina Faso although their long-term effects on seedling recruitment are poorly documented. A factorial experiment involving fire, grazing and cutting, each with two levels, was established in 1992 to study the effects of these management regimes and their interactions on the regeneration of woody species, and examine whether their effects varied temporally. Species richness, density and the morphology of seedlings were assessed in 1997 and 2002, and their relative changes were determined. The change in species richness of multi-stemmed individuals was significantly higher (P = 0.018) on plots that received fire × cutting treatment than the control plots. Significantly more species with single-stem were found on unburnt than on burnt plots (P < 0.001). Grazing tended to reduce the change in total density while fire (P < 0.001) and grazing (P = 0.029) significantly reduced the change in density of single-stemmed individuals. Selective cutting did not affect the total seedling density, but tended to reduce the change in single-stemmed seedling density. Principal component analysis revealed species-specific responses to treatments, particularly the relatively high abundance of lianas compared with other species. Résumé Les feux annuels précoces, la coupe sélective d'arbres et l'exclusion du pâturage sont des moyens actuellement utilisés dans la gestion de la savane soudanienne du Burkina Faso, mais leurs effets à long terme sur le recrutement de jeunes plants sont encore mal documentés. Une expérience factorielle impliquant le feu, le pâturage et la coupe, chacun à deux niveaux, a été mis en place en 1992 pour étudier les effets de ces régimes de gestion et leurs interactions sur la régénération d'espèces ligneuses et pour voir si ces effets variaient de façon temporelle. La richesse spécifique, la densité et la morphologie des jeunes plants furent évaluées en 1997 et en 2002, et l'on a leurs changements relatifs déterminés. Le changement de la richesse spécifique des individus multicoles était significativement plus important (P = 0.018) dans les parcelles qui avaient subi le traitement feu × coupe que dans les parcelles témoins. On a trouvé significativement plus d'espèces à tige unique dans les parcelles non brûlées que dans les parcelles brûlées (P < 0.001). Le pâturage avait tendance à réduire le changement de densité totale alors que le feu (P < 0.001) et le pâturage (P = 0.029) réduisaient significativement le changement de densité des individus à tige unique. La coupe sélective n'affectait pas la densité totale des jeunes plants mais avait tendance à réduire le changement de la densité des plants à tige unique. L'analyse en composantes principales a révélé que les réponses aux différents traitements étaient spécifiques aux espèces, particulièrement l'abondance de lianes, relativement grande par rapport aux autres espèces. [source]

Grazing effect on diversity of annual plant communities in a semi-arid rangeland: interactions with small-scale spatial and temporal variation in primary productivity

JOURNAL OF ECOLOGY, Issue 6 2002
Yagil Osem
Summary 1The interactive effect of grazing and small-scale variation in primary productivity on the diversity of an annual plant community was studied in a semiarid Mediterranean rangeland in Israel over 4 years. The response of the community to protection from sheep grazing by fenced exclosures was compared in four neighbouring topographic sites (south- and north-facing slopes, hilltop and wadi (dry stream) shoulders), differing in vegetation, physical characteristics and soil resources. The herbaceous annual vegetation was highly diverse, including 128 species. Average small-scale species richness of annuals ranged between 5 and 16 species within a 20 × 20 cm quadrat, and was strongly affected by year and site. 2Above-ground potential productivity at peak season (i.e. in fenced subplots) was typical of semiarid ecosystems (10,200 g m,2), except on wadi shoulders (up to 700 g m,2), where it reached the range of subhumid grassland ecosystems. Grazing increased richness in the high productivity site (i.e. wadi), but did not affect, or reduced, it in the low productivity sites (south- and north-facing slopes, hilltop). Under grazing, species richness was positively and linearly related to potential productivity along the whole range of productivity. Without grazing, this relationship was observed only at low productivity (< 200 g m,2). 3The effect of grazing along the productivity gradient on different components of richness was analysed. At low productivity, number of abundant, common and rare species all tended to increase with productivity, both with and without grazing. Rare species increased three times compared with common and abundant species. At high productivity, only rare species continued to increase with productivity under grazing, while in the absence of grazing species number in the different abundance groups was not related to productivity. 4In this semiarid Mediterranean rangeland, diversity of the annual plant community is determined by the interaction between grazing and small-scale spatial and temporal variation in primary productivity, operating mainly on the less abundant species in the community. [source]

RUNOFF NUTRIENT AND FECAL COLIFORM CONTENT FROM CATTLE MANURE APPLICATION TO FESCUE PLOTS,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 4 2000
D. R. Edwards
ABSTRACT: Grazed pastures represent a potential source of non-point pollution. In comparison to other nonpoint sources (e.g., row-cropped lands), relatively little information exists regarding possible magnitudes of pollution from grazed pasture; how that pollution is affected by weather, soil, management and other variables; and how the pollution can be minimized. The objective of this study was to assess how the quality of runoff from fescue plots is influenced by duration of cattle manure application (4,12 weeks) and manure application strategy (none, weekly application of 1.4 kg/plot, and monthly application at 5.6 kg/plot). Additional analyses were performed to relate runoff quality to the timing of sample collection. The study was conducted at the University of Kentucky Maine Chance Agricultural Experiment Station north of Lexington. Plots (2.4 m wide by 6.1 m long) were constructed and established in Kentucky 31 fescue (Festuca arundinacea Schreb.) to represent pasture. Grazing was simulated by application of beef cattle manure to the plots. Runoff was generated by applying simulated rainfall approximately 4, S and 12 weeks following initiation of manure application. Runoff samples were collected and analyzed according to standard methods for nitrogen (N), phosphorus (P) and fecal coliforms (FC). Runoff concentrations of N and P from manure-treated plots were low and generally not consistently different from control plot concentrations or related to manure application strategy. Runoff FC concentrations from manure-treated plots were higher than from control plot concentrations. Runoff concentrations of ammonia N, total Kjeldahl N, ortho-P and FC decreased approximately exponentially in response to increasing time of sample collection. These findings suggest that manure deposition on well-managed pasture at the rates used in this study might have a negligible impact on nutrient content of runoff. [source]

Effects of browsing and grazing on cyclic succession in nutrient-limited ecosystems

JOURNAL OF VEGETATION SCIENCE, Issue 6 2001
Jan Bokdam
van der Meijden (1990) Abstract. This paper deals with browsing and grazing as forces driving cyclic succession. Between 1989 and 1994 reciprocal transitions between the dwarf shrub Calluna vulgaris and the grass Deschampsia flexuosa were monitored in permanent plots in a cattle grazed grass-rich Dutch heathland on podsolic soils in which tree encroachment was prevented. Heather beetles killed Calluna in four of the nine plots during 1991/1992. The monitoring revealed reciprocal transitions and cycles between Calluna and Deschampsia on a subplot scale. Beetles and cattle had additional and complementary effects on the two competing species. Defoliation by beetles and trampling by cattle-killed Calluna and favoured grass invasion. Grazing and gap creation by cattle in Deschampsia favoured the establishment and recovery of Calluna. Analysis of the causal mechanisms suggests that indirect, resource-mediated herbivory effects may be as important for the replacement processes as direct effects of defoliation and trampling. Herbivory created differential light and nutrient levels in Calluna and Deschampsia gaps. Grazing and browsing improved the resource-capturing abilities of Calluna and its resistance to herbivory and abiotic disturbances. The emerged Calluna-Deschampsia cycle and its driving forces are summarized in a conceptual triangular resource-mediated successional grazing cycle (RSGC) model, a limit cycle involving herbivore-plant-plant resource interactions. It offers a deterministic equilibrium model as alternative for stochastic transitions between the meta-stable states with dominance of Calluna and Deschampsia respectively. The validity range of the RSGC model and its management implications are briefly discussed. [source]

Association of Season and Pasture Grazing with Blood Hormone and Metabolite Concentrations in Horses with Presumed Pituitary Pars Intermedia Dysfunction

JOURNAL OF VETERINARY INTERNAL MEDICINE, Issue 5 2010
N. Frank
Background: Pituitary pars intermedia dysfunction (PPID) is a risk factor for pasture-associated laminitis, which follows a seasonal pattern. Hypothesis: Hormonal responses to season differ between PPID and unaffected horses. Animals: Seventeen horses aged 8,30 years (14 horses , 20 years of age). Methods: Longitudinal observational study. Blood was collected monthly from August 2007 until July 2008 after pasture grazing and again after overnight stall confinement. Blood hormone and metabolite concentrations were measured and pasture grass samples were analyzed to determine carbohydrate content. Analysis of variance analysis for repeated measures was performed. Results: Mean ACTH concentrations varied significantly over time (P < .001), with higher concentrations detected in August, September, and October compared with November,April. Pasture × time effects were detected for glucose and insulin concentrations, with peaks observed in September. Horses were retrospectively allocated to PPID (n = 8) and control (n = 9) groups on the basis of plasma ACTH concentrations. Changes in insulin concentrations over time differed in the PPID group when compared with the control group. Insulin concentrations were positively correlated with grass carbohydrate composition. Conclusions and Clinical Importance: PPID did not affect the timing or duration of the seasonal increase in ACTH concentrations, but higher values were detected in affected horses. Insulin concentrations differed between groups, but hyperinsulinemia was rarely detected. Glucose and insulin concentrations peaked in September when horses were grazing on pasture, which could be relevant to the seasonal pattern of laminitis. [source]

Dynamics of grazing lawn formation: an experimental test of the role of scale-dependent processes

OIKOS, Issue 10 2008
Joris P. G. M. Cromsigt
Grazing lawns are characteristic for African savanna grasslands, standing out as intensely grazed patches of stoloniferous grazing-tolerant grass species. Grazing lawn development has been associated with grazing and increased nutrient input by large migratory herds. However, we argue that in systems without mass migrations disturbances, other than direct grazing, drive lawn development. Such disturbances, e.g. termite activity or megaherbivore middens, also increase nutrient input and keep the bunch vegetation down for a prolonged time period. However, field observations show that not all such disturbances lead to grazing lawns. We hypothesize that the initial disturbance has to be of a minimal threshold spatial scale, for grazing intensity to be high enough to induce lawn formation. We experimentally tested this idea in natural tall savanna grassland. We mowed different-sized plots to simulate initial disturbances of different scales (six times during one year) and applied fertilizer to half of the plots during two years to simulate increased nutrient input by herbivores or termite activity. Allowing grazing by naturally occurring herbivores, we followed the vegetation development over more than three years. Grazing kept bunch grass short in coarser, fertilized plots, while grasses grew out toward their initial height in fine-scale and unfertilized plots. Moreover, lawn grasses strongly increased in cover in plots with an increased nutrient input but only after coarser scale disturbance. These results support our hypothesis that an increased nutrient input in combination with grazing indeed induces grazing lawn formation, but only above a threshold scale of the initial disturbance. Our results provide an alternative mechanism for the development of grazing lawns in systems that lack mass migrating herds. Moreover, it gives a new spatial dimension to the processes behind grazing lawn development, and hence help to understand how herbivores might create and maintain spatial heterogeneity in grassland systems. [source]

Translocations as a Tool for Restoring Populations of Bighorn Sheep

RESTORATION ECOLOGY, Issue 4S 2000
Francis J. Singer
Abstract We analyzed factors that contributed to the success of 100 translocations of bighorn sheep within six western states between 1923 and 1997. We categorized the populations as unsuccessful (i.e., extirpated or remnant, <29 animals), moderately successful (30,99 animals), and successful (100,350 animals) by the end of the study period in 1997. Thirty of the translocated populations were unsuccessful (n = 13 were extirpated and n = 17 were remnant), 29 were moderately successful, and 41 were successful (21 ± 1.3 [SE] years of information per translocation). Translocations were less successful when domestic sheep were located within 6 km of the known bighorn sheep use areas (logistic regression, p = 0.052). Grazing of cattle on the same range also negatively influenced success (p = 0.004). Use of indigenous versus previously translocated source stocks increased success (p = 0.084). The translocation was twice as likely to be successful when indigenous herds were used as sources (p = 0.043), but mixing genetic stocks (p = 0.381) or later additional augmentations did not influence success (p = 0.095). Annual migrations by newly established translocated populations increased success (p = 0.014). We recommend translocations of founder groups of bighorn sheep from indigenous sources into large patches of habitat that promote movements and migrations, and with no domestic sheep present in the area. [source]

Biodiversity of semi-arid Mediterranean grasslands: Impact of grazing and afforestation

APPLIED VEGETATION SCIENCE, Issue 2 2007
M.A. Alrababah
Zohary & Feinbrun (1966,1986) Abstract Question: What is the impact of grazing and/or afforestation on grassland diversity, species composition and cover parameters? Location: Semi-arid Mediterranean grasslands of Jordan. Methods: Vegetation, litter, bare soil and rock cover were compared among four management types , free grazing and protected from grazing with three levels of tree cover. Species composition, plant cover, species richness and evenness were used to evaluate differences in vegetation among management types. Species composition differences among management types were also investigated. Results: Semi-arid Mediterranean grasslands harbour appreciable levels of plant biodiversity. Grazing did not affect plant diversity, indicating the high resilience against and adaptation to grazing; however,grazing affected species composition and cover parameters. Afforestation seems to protect soil through higher litter cover but its impact on plant biodiversity was negative and markedly affected species composition. Conclusions: Neither protection from grazing or massive afforestation alone are sufficient for conserving biodiversity in this system. A management model is suggested where the landscape should be maintained as a mosaic of four management types: complete protection from grazing, grazing rotation, planting sparse trees in eroded areas and revegetating degraded areas using native, herbaceous and grazing tolerant species. [source]

Grazing without grasses: Effects of introduced livestock on plant community composition in an arid environment in northern Patagonia

APPLIED VEGETATION SCIENCE, Issue 1 2006
Mariana Tadey
Abstract Question: How does grazing intensity affect plant density, cover and species richness in an Patagonian arid ecosystem? Location: Monte steppe ecoregion, SW Argentina. Methods: I analysed the effect of grazing on plant density, cover and species richness using a stocking rate gradient within the same habitat. Six paddocks were used with stocking rates ranging between 0.002 , 0.038 livestock/ha. Plant density, species richness, plant cover and percentage of grazed branches were determined by sampling plots within each paddock. The percentage of grazed branches was used as an independent measurement of grazing intensity. Results: Higher stocking rates were related to lower plant density, species richness and plant cover. The paddock with the lowest grazing intensity had 86% more plants per unit area, 63% more plant cover and 48% higher species richness. The percentage of grazed branches and the quantity of dung increased with stocking rate. Conclusions: Introduced livestock seriously affect native vegetation in the Patagonian Monte. The damage observed in this xerophytic plant community suggests that plant adaptations to aridity do not provide an advantage to tolerate or avoid grazing by vertebrate herbivores in this region. Plant degradation in this arid environment is comparable to the degradation found in more humid ecosystems. [source]

Vegetation change in a man-made salt marsh affected by a reduction in both grazing and drainage

APPLIED VEGETATION SCIENCE, Issue 1 2002
Peter Esselink
Abstract. In order to restore natural salt marsh in a 460-ha nature reserve established in man-made salt marsh in the Dollard estuary, The Netherlands, the artificial drainage system was neglected and cattle grazing reduced. Vegetation changes were traced through two vegetation surveys and monitoring of permanent plots over 15 yr after the management had been changed. Exclosure experiments were started to distinguish grazing effects from effects of increased soil waterlogging caused by the neglect of the drainage system. Both vegetation surveys and permanent plots demonstrated a dichotomy in vegetation succession. The incidence of secondary pioneer vegetation dominated by Salicornia spp. and Suaeda maritima increased from 0 to 20%, whereas the late-successional (Phragmites australis) vegetation from 10 to 15%. Grazing intensity decreased towards the sea. The grazed area contracted landward, which allowed vegetation dominated by tall species to increase seaward. Grazing and increased waterlogging interacted in several ways. The impact of trampling increased, and in the intensively grazed parts soil salinity increased. This can probably be explained by low vegetation cover in spring. Framework Ordination, an indirect-gradient-analysis technique, was used to infer the importance of environmental factors in influencing changes in species composition. Many changes were positively or negatively correlated with soil aeration and soil salinity, whereas elevation was of minor importance. Grazing accounted for only a few changes in species frequency. Changes in permanent plots were greater during the first than during the second half of the study period. In exclosures that were installed halfway through the study period, there was a relatively rapid recovery of previously dominant species that had decreased during the first half of the study period. Species richness per unit area in the reserve increased. At the seaward side of the marsh, the altered management allowed succession to proceed leading to establishment of stands of Phragmites australis, whereas on the landward side, the combination of moderate grazing with neglect of the drainage system appeared an effective measure in maintaining habitats for a wider range of halophytic species. [source]

The Ecology of Browsing and Grazing

AUSTRAL ECOLOGY, Issue 2 2010
BEN MOORE
No abstract is available for this article. [source]

Grazing and landscape controls on nitrogen availability across 330 South African savanna sites

AUSTRAL ECOLOGY, Issue 7 2009
JOSEPH M. CRAINE
Abstract The availability of nitrogen (N) is an important determinant of ecosystem and community dynamics for grasslands and savannas, influencing factors such as biomass productivity, plant and herbivore composition, and losses of N to waters and the atmosphere. To better understand the controls over N availability at landscape to regional scales, we quantified a range of plant and soil characteristics at each of 330 sites in three regions of South Africa: Kruger National Park (KNP), private game reserves adjacent to KNP (private protected areas , PPAs) and Hluhluwe-iMfolozi Park (HiP). In comparing regions and sites within regions, grazing appeared to have a strong influence on N availability. Sites in the PPAs adjacent to KNP as well as sodic and alluvial sites in general typically had the highest N availability. The high N availability of these sites was not generally associated with greater potential N mineralization, but instead with less grass biomass and more forb biomass that indicated greater grazing pressure. Whereas sodic sites had a long history of high N availability as evidenced by their high soil ,15N, the greater N availability in the PPAs over the two parks appeared to be relatively recent. Grazer biomass, average potential mineralization rates and grass biomass for HiP were greater than KNP, yet there were no differences in N availability as indexed by soil and foliar ,15N between sites in the two parks. Although the short-term increase in N availability in PPAs is not necessarily deleterious, it is uncertain whether current productivity levels in those ecosystems is sustainable. With differences in management causing herbivore biomass to be 150% greater in the PPAs than the adjacent KNP, changes in plant communities and nitrogen cycling might lead to long-term degradation of these ecosystems, their ability to sustain herbivore populations, and also serve as an economic resource for the region. [source]

Biophysical and human influences on plant species richness in grasslands: Comparing variegated landscapes in subtropical and temperate regions

AUSTRAL ECOLOGY, Issue 3 2001
S. Mcintyre
Abstract A survey of grassy woodlands in the Queensland subtropics was conducted, recording herbaceous species richness at 212 sites on three properties (2756 ha). A range of habitats typical of cattle grazing enterprises was sampled and site variables included lithology, slope position, tree density, soil disturbance, soil enrichment and grazing. Results were compared with a previously published survey of temperate grasslands. Lithology, slope position and tree density had relatively minor effects on plant species richness, although in both surveys there was some evidence of lower species richness on the more fertile substrates. Soil disturbance and soil enrichment significantly reduced the richness of native species in both surveys, while exotic species were insensitive (subtropics) or increased (temperate) with disturbance. Rare native species were highly sensitive to disturbances, including grazing, in the temperate study. Although some trends were similar for rare species in the subtropics, the results were not significant and there were complex interactions between grazing, lithology and slope position. Grazing did not have a negative effect on native species richness, except in the closely grazed patches within pastures, and then only on the most intensively developed property. At the scale recorded (30 m2), the native pastures, roadsides and stock routes sampled in the subtropics appear to be among the most species-rich grasslands ever reported, both nationally and globally. Native species richness was approximately 50% higher than the temperate survey figures across all the comparable habitats. While there are no clear reasons for this result, potential explanations are proposed. [source]

Bayesian Networks and Adaptive Management of Wildlife Habitat

CONSERVATION BIOLOGY, Issue 4 2010
ALISON L. HOWES
herramientas para la toma de decisiones; incertidumbre ecológica; pastoreo feral; regímenes de quema; validación de modelos Abstract:,Adaptive management is an iterative process of gathering new knowledge regarding a system's behavior and monitoring the ecological consequences of management actions to improve management decisions. Although the concept originated in the 1970s, it is rarely actively incorporated into ecological restoration. Bayesian networks (BNs) are emerging as efficient ecological decision-support tools well suited to adaptive management, but examples of their application in this capacity are few. We developed a BN within an adaptive-management framework that focuses on managing the effects of feral grazing and prescribed burning regimes on avian diversity within woodlands of subtropical eastern Australia. We constructed the BN with baseline data to predict bird abundance as a function of habitat structure, grazing pressure, and prescribed burning. Results of sensitivity analyses suggested that grazing pressure increased the abundance of aggressive honeyeaters, which in turn had a strong negative effect on small passerines. Management interventions to reduce pressure of feral grazing and prescribed burning were then conducted, after which we collected a second set of field data to test the response of small passerines to these measures. We used these data, which incorporated ecological changes that may have resulted from the management interventions, to validate and update the BN. The network predictions of small passerine abundance under the new habitat and management conditions were very accurate. The updated BN concluded the first iteration of adaptive management and will be used in planning the next round of management interventions. The unique belief-updating feature of BNs provides land managers with the flexibility to predict outcomes and evaluate the effectiveness of management interventions. Resumen:,El manejo adaptativo es un proceso interactivo de recopilación de conocimiento nuevo relacionado con el comportamiento de un sistema y el monitoreo de las consecuencias ecológicas de las acciones de manejo para refinar las opciones de manejo. Aunque el concepto se originó en la década de los 1970s, rara vez es incorporado activamente en la restauración ecológica. Las redes Bayesianas (RBs) están emergiendo como herramientas eficientes para la toma de decisiones ecológicas en el contexto del manejo adaptativo, pero los ejemplos de su aplicación en este sentido son escasos. Desarrollamos una RB en el marco del manejo adaptativo que se centra en el manejo de los efectos del pastoreo feral y los regímenes de quemas prescritas sobre la diversidad de aves en bosques subtropicales del este de Australia. Construimos la RB con datos para predecir la abundancia de aves como una función de la estructura del hábitat, la presión de pastoreo y las quemas prescritas. Los resultados del análisis de sensibilidad sugieren que la presión de pastoreo incrementó la abundancia de melífagos agresivos, que a su vez tuvieron un fuerte efecto negativo sobre paserinos pequeños. Posteriormente se llevaron a cabo intervenciones de manejo para reducir la presión del pastoreo feral y quemas prescritas, después de las cuales recolectamos un segundo conjunto de datos de campo para probar la respuesta de paserinos pequeños a estas medidas. Utilizamos estos datos, que incorporaron cambios ecológicos que pueden haber resultado de la intervención de manejo, para validar y actualizar la RB. Las predicciones de la abundancia de paserinos pequeños bajo las nuevas condiciones de hábitat y manejo fueron muy precisas. La RB actualizada concluyó la primera iteración de manejo adaptativo y será utilizada para la planificación de la siguiente ronda de intervenciones de manejo. La característica única de actualización de la RBs permite que los manejadores tengan flexibilidad para predecir los resultados y evaluar la efectividad de las intervenciones de manejo. [source]