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Disturbed Habitats (disturbed + habitat)

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Selected Abstracts

Effects of Habitat Disturbance on Stream Salamanders: Implications for Buffer Zones and Watershed Management

CONSERVATION BIOLOGY, Issue 3 2003
John D. Willson
To minimize the impacts of development on aquatic habitats, numerous conservation measures have been implemented, including the use of riparian buffer zones along streams and rivers. We examined the effectiveness of current buffer-zone systems for management of small watersheds in conserving stream-dwelling salamander populations in 10 small streams ( draining <40.5 ha ) in the western Piedmont of North Carolina. We captured salamanders by means of funnel traps and systematic dipnetting and used a geographic information system to calculate the percentage of disturbed habitat within the watershed of each stream and within 10.7-, 30.5-, and 61.0 -m buffer zones around each stream, upstream from our sampling locations. Although the relative abundance of salamanders was strongly inversely proportional to the percentage of disturbed habitat in the entire watersheds ( R2 = 0.71 for Desmognathus fuscus and 0.48 for Eurycea cirrigera ), we found little to no correlation between the relative abundance of salamanders and the percentage of disturbed habitat present within buffer zones ( R2 = 0.06,0.27 for D. fuscus and 0.01,0.07 for E. cirrigera ). Thus, conservation efforts aimed at preserving salamander populations in headwater streams must consider land use throughout entire watersheds, rather than just preserving small riparian buffer zones. Resumen: La destrucción y degradación del hábitat se encuentra entre la mayores amenazas a la vida silvestre, junto con el aumento global de la población humana. Para minimizar los impactos del desarrollo sobre hábitats acuáticos, se han instrumentado numerosas medidas de conservación, incluyendo el uso de zonas de amortiguamiento riparias a lo largo de arroyos y ríos. Examinamos la efectividad de los actuales sistemas de zonas de amortiguamiento usados en el manejo de cuencas pequeñas para la conservación de poblaciones de salamandras de arroyo en 10 arroyos pequeños ( que drenan <40.5 ha ) al pie de monte del occidente de Carolina del Norte. Capturamos salamandras con trampas de embudo y mediante el uso sistemático de redes y utilizamos un sistema de información geográfica para calcular el porcentaje de hábitat perturbado dentro de la cuenca de cada arroyo y dentro de zonas de amortiguamiento de 10.7-, 30.5- y 61.0-m alrededor de cada arroyo, río arriba de nuestros sitios de muestreo. Aunque los valores de abundancia relativa de salamandras fueron inversamente proporcionales al porcentaje de hábitat perturbado en el total de las cuencas ( R2 = 0.71 para Desmognathus fuscus y 0.48 para Eurycea cirrigera ), encontramos una correlación débil o inexistente entre las abundancias relativas de salamandras y el porcentaje de hábitat perturbado en las zonas de amortiguamiento R2 = 0.06,0.27 para D. fuscus y 0.01,0.07 para E. cirrigera ). Por lo tanto, los esfuerzos de conservación dirigidos a preservar poblaciones de salamandras de arroyos de cabecera deben tomar en cuenta el uso de la tierra en la superficie entera de las cuencas, en lugar de preservar pequeñas zonas de amortiguamiento riparias. [source]

Seed predation, not seed dispersal, explains the landscape-level abundance of an early-successional plant

JOURNAL OF ECOLOGY, Issue 4 2006
JOHN L. ORROCK
Summary 1Plants may not occur in a given area if there are no suitable sites for seeds to establish (microsite limitation), if seeds fail to arrive in suitable microsites (dispersal limitation) or if seeds in suitable microsites are destroyed by predators (predator limitation). 2We conducted a large-scale study to determine the importance of dispersal limitation and predator limitation in affecting the distribution of pokeweed, Phytolacca americana, in 401-ha experimental patches arrayed in eight groups of five patches distributed across a 300-km2 region. 3Microsite limitation was minimized by clearcutting and burning existing vegetation, creating the type of disturbed habitat in which P. americana readily germinates and establishes. The role of dispersal limitation was examined by adding approximately 7000 seeds to each of eight patches in March 2000. The role of seed predation was examined in all 40 patches using experimental exclosures from June 2000 to July 2001. 4The number of P. americana plants in September 2000 was unchanged by seed addition. However, fewer P. americana plants were found in patches where seed predators removed more P. americana seeds from experimental exclosures. These data suggest that P. americana is not limited by seed dispersal. Rather, in habitats where microsites are readily available, the abundance of P. americana among patches appears to be limited by the activities of seed predators. 5When dispersal and microsites are not limiting, the role of local seed predators can be important for generating emergent, large-scale patterns of plant abundance across landscapes. Moreover, because predators may generate large-scale patterns that resemble other forms of limitation and predators may target specific species, predator impacts should be more frequently incorporated into experiments on the role of seed limitation and plant community composition. [source]

Anthropogenic disturbance promotes hybridization between Banksia species by altering their biology

JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2003
B. B. Lamont
Abstract Putative hybrids between Banksia hookeriana and B. prionotes were identified among 12 of 106 populations of B. hookeriana located at or near anthropogenically disturbed sites, mainly roadways, but none in 156 undisturbed populations. Morphometrics and AFLP markers confirmed that a hybrid swarm existed in a selected disturbed habitat, whereas no intermediates were present where the two species co-occurred in undisturbed vegetation. Individuals of both species in disturbed habitats at 12 sites were more vigorous, with greater size and more flower heads than their counterparts in undisturbed vegetation. These more fecund plants also showed a shift in season and duration of flowering. By promoting earlier flowering of B. hookeriana plants and prolonging flowering of B. prionotes, anthropogenic disturbance broke the phenological barrier between these two species. We conclude that anthropogenic disturbance promotes hybridization through increasing opportunities for gene flow by reducing interpopulation separation, increasing gamete production and, especially, promoting coflowering. [source]

Variation in physiological health of diademed sifakas across intact and fragmented forest at Tsinjoarivo, eastern Madagascar

AMERICAN JOURNAL OF PRIMATOLOGY, Issue 11 2010
Mitchell T. Irwin
Abstract As undisturbed habitat becomes increasingly rare, managers charged with ensuring the survival of endangered primate species must increasingly utilize disturbed and degraded habitats in species survival plans. Yet we have an imperfect understanding of the true long-term viability of primate populations in disturbed habitat, and census data can be misleading because density is not necessarily correlated with habitat quality and population viability in predictable ways. Here we present clinical laboratory data on hematology, serum biochemistry, fat-soluble vitamins, minerals, iron analytes, viral serology, and parasitology of diademed sifaka (Propithecus diadema), derived from the capture of 26 individuals spanning eight groups and two habitats (undisturbed vs. disturbed and fragmented) at Tsinjoarivo, Madagascar. Blood from fragment individuals had significantly lower values for several factors: white blood cell counts, bilirubin, total protein, albumin, calcium, sodium, chloride, manganese, zinc, iron and total iron-binding capacity. Several biochemical variables were higher in immature individuals, probably due to active growth. The large number of interhabitat differences suggests that habitat disturbance has an impact on physiological health within this population, perhaps reflecting dietary stress and/or immunosuppression. These results, combined with previous data showing altered diet, slower juvenile growth, and reduced activity in disturbed forest fragments, suggest that fragment sifakas may be less healthy than continuous forest groups. Finally, Tsinjoarivo sifakas have extremely low blood urea nitrogen (perhaps reflecting protein limitation) and selenium levels relative to other lemurs. Despite their survival and reproduction in the short term in fragments, these sifakas may represent a riskier conservation investment than conspecifics in undisturbed forest, and may be more susceptible to environmental stressors. However, more data on the fitness consequences of these biochemical differences are needed for a better interpretation of their impacts on long-term viability prospects. Am. J. Primatol. Am. J. Primatol. 72:1013,1025, 2010. © 2010 Wiley-Liss, Inc. [source]

Habitat-specific ranging patterns of Dian's tarsiers (Tarsius dianae) as revealed by radiotracking

AMERICAN JOURNAL OF PRIMATOLOGY, Issue 2 2006
Stefan Merker
Abstract Dian's tarsier Tarsius dianae, one of the smallest primates on earth, is endemic to the central regions of Sulawesi, Indonesia. To evaluate the effects of increasing land use by humans on the ranging patterns of this nocturnal insect hunter, four study plots along a gradient of anthropogenic disturbance were selected for this study. In these plots, 71 tarsiers were captured with mist nets, and 30 of these were fitted with 3.9 g radiotransmitters and subsequently tracked over the course of 2 weeks per animal. The average home ranges were 1.1,1.8 ha in size, with the smallest ranges in slightly disturbed habitat and the largest ranges in a heavily disturbed plantation. These findings coincide with different estimates of insect abundance in the study plots. Nightly travel distances were smallest in undisturbed old-growth forest and slightly increased along a gradient of human disturbance. The tarsiers were most active shortly after dusk and just before dawn. The results of this comprehensive radiotracking study on tarsiers show that T. dianae adapts its ranging behavior to the degree and type of human land use. Integrated data on home range size and travel distance indicate that slightly disturbed forest is as favorable to these animals as undisturbed habitat. However, with increasing anthropogenic effects, the living conditions of the tarsiers appear to deteriorate, resulting in the necessity for larger home and night ranges. The results of this study provide an important tool for directing conservation efforts targeted at the survival of this primate in central Sulawesi. Am. J. Primatol. 68:111,125, 2006. © 2006 Wiley-Liss, Inc. [source]

Developmental changes in factors limiting colony survival and growth of the leaf-cutter ant Atta laevigata

ECOGRAPHY, Issue 3 2010
Ernane H. M. Vieira-Neto
Many species of leaf-cutter ants (Atta and Acromyrmex) increase in abundance following natural or anthropogenic disturbances in the vegetation. However, the mechanisms responsible for such an increase are still poorly understood. We evaluated the effects of nesting site and the availability of palatable forage on survival and growth of Atta laevigata colonies at different developmental stages. Foundress queens transplanted into man-made clearings (dirt roads) had a much higher survival than those transplanted into the adjacent undisturbed savannah vegetation. Similarly, incipient colonies (,3-months old) had significantly greater survival and growth rates in dirt roads. In contrast, nesting site did not influence performance of young colonies (,15-months old). Both incipient and young colonies responded strongly and positively to experimental supplementation of palatable forage, and this effect was independent of the nesting habitat. Colonies that received extra food grew faster and had a significantly greater survival rate than control colonies. These results suggest that performance of A. laevigata is affected by the generally greater availability of suitable nesting sites and palatable vegetation in disturbed habitats. This may explain how these ants maintain high densities in these habitats, and since the relative importance of these factors changed with colony ontogeny, our findings highlight the importance of evaluating potential limiting factors throughout the full range of an organism's developmental stages. [source]

Fish distribution and diet in relation to the invasive macrophyte Lagarosiphon major in the littoral zone of Lake Dunstan, New Zealand

ECOLOGY OF FRESHWATER FISH, Issue 1 2008
T. O. Bickel
Abstract,,, Invasive macrophytes are usually associated with negative impacts on habitat quality and a threat to native biodiversity. However, they might provide the same beneficial functions of native macrophytes, i.e., the provision of food and shelter for fish, in the absence of native macrophytes. To assess the value of the invasive macrophyte Lagarosiphon major as a fish habitat, we investigated the spatio,temporal variation in the distribution of a small littoral fish species (common bully) in the littoral of Lake Dunstan, a New Zealand hydro lake. Large- and fine-scale common bully distribution could partly be explained by the occurrence of dense L. major stands. Additionally, variability in catch per unit effort was partly explained by season and recruitment. Diet analysis indicated that common bullies in the Lagarosiphon-dominated littoral fed on invertebrates (Mollusca, Trichoptera, Chironomidae) found on exotic L. major, therefore suggesting its role as a food provider in the system. These results indicated that invasive macrophytes can provide important ecosystem functions in disturbed habitats that are otherwise devoid of native macrophytes. Any macrophyte management strategy should therefore carefully consider the costs and benefits associated with macrophyte control. [source]

Biodiversity and resource use of larval chironomids in relation to environmental factors in a large river

FRESHWATER BIOLOGY, Issue 6 2002
CHRISTIAN FESL
1.,Larval chironomids were examined at four sites on a cross-section of the River Danube in Austria between September 1995 and August 1996. The sites differed in hydraulics, sediment composition and habitat stability. 2.,Species,accumulation curves, showing the increase in number of species with increasing sampling effort, from three main channel sites were best described by a logarithmic model, suggesting that most of the species occurring at these sites were found. Data from a site connected to a backwater fitted best to a power model, indicating a random assemblage with additional species immigrating from the backwater area. 3.,Properties of the community were estimated using Jackknife techniques: species richness (range of mean values at the four sites: 32,91), H, diversity (1.5,2.3), evenness (0.23,0.28), spatial resource width (0.01,0.06), spatial resource overlap (0.13,0.20), spatial species aggregation (0.60,0.77), temporal community persistence (Kendal's correlation coefficient: 0.47,0.60) and beta-diversity (6.2,9.7). 4.,Redundancy analysis (RDA) was used to relate the community properties and species abundance to environmental factors. Habitat stability was the major factor associated with community structure. Higher sediment turnover led to higher spatial aggregation and, consequently, a decrease in spatial resource width and overlap, and to a decline in larval density and species richness. 5.,Species-abundance patterns agreed well with the log-normal model. Moderate community persistence and stability of the streambed sediments suggest that the log-normal model may be a good descriptor for communities of intermediately disturbed habitats, like large rivers, rather than stable habitats. [source]

Impacts of land use change on South-east Asian forest butterflies: a review

JOURNAL OF APPLIED ECOLOGY, Issue 4 2007
LIAN PIN KOH
Summary 1South-east Asia has the highest relative rate of habitat loss and degradation in the humid tropics. The responses of less ,charismatic' groups, including butterflies, to habitat disturbance remain relatively poorly understood. Many South-east Asian butterflies are endemic to the region and face global extinction if current levels of deforestation were to continue. 2Here, I highlight South-east Asia as a region urgently in need of butterfly conservation research and review empirical studies of the responses of South-east Asian butterflies to land use change. Additionally, I discuss some methodological pitfalls for such studies. Furthermore, I argue for the importance of identifying the ecological correlates of sensitivity of butterfly species to forest modification and the potential biological mechanisms underlying their responses to land use change. 3There has been no consensus among previous studies on the effects of land use change on butterfly communities in South-east Asia. Of the 20 studies I reviewed, seven reported higher species richness/diversity in undisturbed (or the least disturbed) forest than in disturbed habitats, nine reported the opposite trend, three reported no difference and one reported a strong influence of seasonality on the impacts of logging. 4Some of these studies may contain inherent methodological biases resulting from the failure to control for sampling effects, the lack of consideration for the spatial scale of analysis and incomplete sampling of the vertical strata in tropical rainforests. 5Synthesis and applications. Empirical studies of the effects of land use change on tropical forest insects are sorely lacking from South-east Asia. Butterflies are an ideal taxonomic group for such investigations. Future studies should be designed carefully to avoid the methodological pitfalls highlighted here. Determining the ecological correlates of sensitivity of butterflies to forest modification is important for the pre-emptive identification of species of conservation concern and for generating testable hypotheses on the differential responses of species to forest modification. Experimental studies are needed to determine the mechanisms underlying the responses of species to land use change in order to develop effective strategies for the conservation of butterflies in human disturbed landscapes. [source]

The biology of insularity: an introduction

JOURNAL OF BIOGEOGRAPHY, Issue 5-6 2002
Donald R. Drake
Insular environments, ranging from oceanic islands to fragments of once-contiguous natural systems, have long been used by biologists to test basic principles of ecology, evolution and biogeography. More recently, insular environments have figured prominently in conservation ecology, where the aim has usually been to conserve species or assemblages unique to isolated habitats. Improving the level of communication among the evolutionary biologists, theoretical ecologists and conservation biologists who study insular biotas will work to the benefit of all. This volume was inspired by a recent conference on the ecology of insular biotas, in which participants from a wide range of disciplines came together to compare ecological processes across a variety of taxonomic groups inhabiting a wide range of isolated environments. In this introduction, we point out the themes underlying these very diverse contributions. First we elaborate on the value of islands for elucidating processes underlying ecosystem functioning, population dynamics of reintroduced species, and restoration of disturbed habitats, and emphasize those areas where the use of islands could be expanded. The second section focuses on the link between ecology and evolutionary processes in insular systems and includes examples from oceanic islands, naturally patchy habitats and recently fragmented habitats. The third section illustrates some of the ways that invasive alien species on oceanic islands affect plant,animal mutualisms, particularly seed dispersal and pollination. The final section, on consequences of habitat fragmentation, focuses mainly on studies that describe the consequences that fragmentation has for plants and animals as they are forced into artificially insular environments. We close with a study that points out the differences among types of insular systems and identifies gaps in our knowledge of insular biotas, particularly the importance of explicitly incorporating patch type, age and patch,matrix contrasts in research. Finally, we recommend a greater emphasis on linking ecological theory and applied research, and improving communication between those who ask basic ecological questions and those who use insular systems for conservation. [source]

The diversity and abundance of North American butterflies vary with habitat disturbance and geography

JOURNAL OF BIOGEOGRAPHY, Issue 4 2000
Scott D. Kocher
Abstract Aim We used data from the annual Fourth of July Butterfly Count for the years 1989,97 to examine patterns of species richness and total butterfly abundance across North America and within topographically diverse and disturbed landscapes. Location We analysed counts from 514 different locations in North America. The counts represent all areas of the USA and southern Canada, with a few Mexican sites as well, although most counts were in the eastern USA. Methods First, we standardized published count data according to the effort expended per count (total party-hours). Using regression analysis and analysis of variance, we then examined the impact of latitude, longitude, topographical relief, habitat disturbance and different climatic measures on the species richness and total abundance of butterflies per count. We also examined the abundance of exotic species in disturbed landscapes. Results Our analyses suggest that: (1) species richness is highest at low latitudes and near Rocky Mountain longitudes; (2) the total abundance of individuals is highest in northern US latitudes and Great Plains longitudes; (3) species richness but not total abundance increases with greater topographical relief; (4) species richness and diversity indices are lower in more disturbed habitats; and (5) the abundance of the introduced Pieris rapae (L.) is greater in more disturbed habitats. Main conclusions Different factors control the abundance and species richness of North American butterflies. Along with geographical location, habitat disturbance and topographical variability affect species richness. Our analysis also shows the value of broad-based monitoring regimes, such as the North American Fourth of July Butterfly Count. [source]

Diet composition of Xenopus borealis in Taita Hills: effects of habitat and predator size

AFRICAN JOURNAL OF ECOLOGY, Issue 2 2010
Beryl A. Bwong
Abstract Frogs in the genus Xenopus are ubiquitous in sub-Saharan Africa, yet very little is recorded on their ecology. They are commonly found in anthropogenically disturbed habitats, but how do these compare to conspecifics from natural habitats? The diet of Xenopus borealis from three different sites in Taita Hills, Kenya was established based on a sample of 77 (54 females and 23 males) specimens from two disturbed and one pristine sites. Xenopus borealis from all the sites was found to be a dietary generalist, feeding predominantly on invertebrates. A total of twelve invertebrate orders both terrestrial and aquatic were recorded in addition to amphibian eggs, tadpoles and fish. Frogs from the pristine forest were smaller and had ingested more terrestrial prey items than frogs in the disturbed open habitat ponds. The stomach content (both by mass and quantity) was independent of body size. The results suggest that X. borealis is an opportunistic generalist predator which may be constrained by food availability in its natural habitat. However, disturbed habitats provide abundant food items which are enough to significantly increase the mean size of the population. Résumé Les grenouilles du genre Xenopus sont présentes partout en Afrique subtropicale, mais il existe peu de travaux sur leur écologie. On les trouve fréquemment dans des habitats perturbés par les hommes, mais comment ces grenouilles-ci se comparent-elles à leurs congénères des habitats naturels ? On a pu établir le régime alimentaire de Xenopus borealis sur trois sites différents des Taita Hills, au Kenya, d'après un échantillon de 77 individus (54 femelles et 23 mâles) de deux sites perturbés et d'un site intact. Xenopus borealis s'est avéréêtre un consommateur généraliste sur tous les sites, se nourrissant principalement d'invertébrés. On a noté la présence d'un total de 12 ordres d'invertébrés, terrestres et aquatiques, auxquels s'ajoutent des ,ufs d'amphibiens, des têtards et des poissons. Les grenouilles des forêts intactes étaient plus petites et mangeaient des proies plus terrestres que celles des points d'eau d'habitats ouverts perturbés. Le contenu stomacal (aussi bien par la masse que par la quantité) était indépendant de la taille corporelle. Les résultats suggèrent que X. borealis est un prédateur généraliste opportuniste qui peut être limité par la disponibilité de la nourriture dans son habitat naturel. Par contre, des habitats perturbés fournissent une nourriture abondante, suffisante pour augmenter significativement la taille moyenne de la population. [source]

Invasive Acacia auriculiformis Benth. in different habitats in Unguja, Zanzibar

AFRICAN JOURNAL OF ECOLOGY, Issue 1 2009
Riitta Kotiluoto
Abstract Acacia auriculiformis Benth., Mimosaceae, has been introduced relatively recently as a plantation tree to the island of Unguja, Zanzibar. It has been reported to establish itself outside the plantations, but it is not known if the success of establishment depends on habitat quality. We investigated the occurrence of A. auriculiformis in 5-m-wide sample lines, which started from the edge of acacia plantations and reached farthermost the distance of 1 km. The results of 7.24 ha studied showed that: (1) A. auriculiformis occurred in most of the studied habitats in Unguja and appeared to be more abundant in deep soils than in shallow coral-derived soils. However, statistical analyses suggested that the species has little preference or avoidance towards any of the habitats, even though forests , the least disturbed habitats , seemed to have less acacias than other more disturbed habitats. (2) The number of acacias decreased rapidly with the distance from an acacia plantation, and most of the found acacias were still young, below three metres tall. Our results suggest that the invasion of A. auriculiformis is at its beginning in Unguja. If no preventive measures are taken, A. auriculiformis may have an increasing impact on local ecosystem in the future. Résumé Acacia auriculiformis Benth., une mimosacée, a été introduit assez récemment sous forme de plantation dans l'île d'Unjuga, à Zanzibar. On a rapporté qu'il s'était établi de lui-même en dehors des plantations, mais on ne sait pas si la réussite de cette installation dépend de la qualité de l'habitat. Nous avons étudié la présence d'Acacia auriculiformis sur des bandes échantillons de cinq mètres de large qui commençaient à la lisière des plantations d'acacia et s'éloignaient jusqu'à un kilomètre. Les résultats obtenus sur les 7,24 ha étudiés montrent que 1) Acacia auriculiformis existe dans la plupart des habitats étudiés à Unjuga et semble plus abondant dans des sols profonds que dans des sols peu profonds dérivés des coraux. Cependant, les analyses statistiques suggèrent que l'espèce montre peu de préférences ou de rejet envers aucun des habitats, même si les forêts , les habitats les moins perturbés , semblent contenir moins d'acacias que d'autres habitats plus perturbés et que 2) le nombre d'acacias diminue rapidement quand on s'éloigne des plantations d'acacias, et que la plupart des acacias trouvés sont encore jeunes et mesurent moins de trois mètres de haut. Nos résultats suggèrent que l'invasion d'Acacia auriculiformis en est encore à ses début sur Unjuga. Si l'on ne prend pas de mesures préventives, A. auriculiformis pourrait avoir un impact croissant sur l'écosystème local dans le futur. [source]

Vernalization requirement of wild beet Beta vulgaris ssp. maritima: among population variation and its adaptive significance

JOURNAL OF ECOLOGY, Issue 4 2002
Pierre Boudry
Summary 1Seven populations of Beta vulgaris ssp. maritima (wild beet) situated along a latitudinal cline were studied for their vernalization requirement and its consequences for fitness. 2Various cold regimes were applied in glasshouses and experimental gardens with plants of different ages. Three additional experimental sites (on the French Mediterranean, Atlantic and North Sea coasts) situated near three of the sampled populations, and thus including a reciprocal transplant design, were used to evaluate the influence of latitude under natural conditions. Survival and plant size were measured over 3 years. 3The vernalization requirement was greater in plants from more northern origins. The level of cold required to allow flowering overcompensated for the colder springs, so that northern plants in northern sites flowered less than southern plants in southern sites. 4Young seedlings were more difficult to vernalize than plants that had already developed vegetative rosettes. 5Differences in vernalization requirement seem to be an adaptive response to spring temperatures and season length in a particular latitude. A whole winter vernalization almost always led to flowering in the subsequent year whatever the latitude or geographical origin. 6Plants from the Atlantic and Channel coasts showed the highest lifetime reproductive success at all sites. Southern populations were better adapted to disturbed habitats as shown by their higher first-year reproductive success. The North Sea population had a lower reproductive success than the Atlantic populations, even in its native environment. [source]

Fruit dispersal and seed banks in Atriplex sagittata: the role of heterocarpy

JOURNAL OF ECOLOGY, Issue 2 2001
Bohumil Mandák
Summary 1Atriplex sagittata, an arly succesional, annual species of disturbed habitats in Central Europe, produces three types of fruits. We studied the differences in dispersal between the fruit types in order to investigate their ecological roles. 2The typical positive relationship between dispersal ability and germinability is not found in this species. Type A (ebracteate) fruits produced deeply dormant seeds and had the lowest dispersal potential, but of the two fruits with bracts, type B, with dormant seeds, was better dispersed by both water and wind than type C, which produces non-dormant seeds. 3Wind, temperature and precipitation have significant effects on fruit release but their effects differ between fruit types. The release of fruit types with bracts was positively correlated with wind whereas all fruit types tended to be negatively correlated with precipitation and temperature range. 4Type C fruit, which contains non-dormant seed, are absent from the soil in summer and have a Type II transient seed bank. Type A and B fruits, containing dormant seeds, form a persistent seed bank. 5Heterocarpy, where fruit types show distinct ecological behaviour, enables colonizing species such as A. sagittata to survive both major disturbance (by ensuring that some seeds persist) and unfavourable conditions (by spreading germination over a long period). 6In A. sagittata, seed dynamics can be explained by the germination behaviour of seeds produced by the three types of fruit. All fruit types mature in autumn, but few of Type A fall from the mother plant until spring, when germination is probably inhibited because of insufficient stratification. Type C fruit, however, show peak dispersal in winter and the majority of these non-dormant seeds are able to germinate as soon as conditions become more suitable. [source]

Anthropogenic disturbance promotes hybridization between Banksia species by altering their biology

Is the productivity of vegetation plots higher or lower when there are more species?

OIKOS, Issue 2 2003
Variable predictions from interaction of the, competitive dominance effect' on the habitat templet, sampling effect'
Using a habitat templet model, we predict that the productivity (total biomass) of plots within a plant community may be positively, negatively or not at all related to variation in the number of species per plot, depending on successional stage (time since major disturbance) and habitat carrying capacity (reflecting the total resource supplying power of the habitat). For plots of a given size, a positive relationship between productivity and species richness is predicted in recently disturbed habitats because local neighbourhoods here will have been assembled largely stochastically, usually from a pool of available species with a right-skewed size frequency distribution. Hence, in the earliest stages of succession, plots will have relatively high total biomass only if they contain at least some of the relatively uncommon larger species which will, in turn, be more likely in those neighbourhoods that contain more species (the sampling effect). Among these will also be some of the more common smaller species; hence, these high biomass, species-rich plots should have relatively low species evenness, in contrast to what is predicted under effects involving species complementarity. In late succession, the plots with high total biomass will still be those that contain relatively large species but these plots will now contain relatively few species owing to increased competitive exclusion over time (the competitive dominance effect). In intermediate stages of succession, no relationship between plot productivity and species richness is predicted because the opposing sampling and competitive dominance effects cancel each other out. We predict that the intensity of both the sampling and competitive dominance effects on the productivity/species richness relationship will decrease with decreasing habitat carrying capacity (e.g. decreasing substrate fertility) owing to the inherently lower variance in between-plot productivity that is predicted for more resource-impoverished habitats. [source]

Pollinators and Reproductive Success of the Wild Cucurbit Cucurbita maxima ssp. andreana (Cucurbitaceae)

PLANT BIOLOGY, Issue 4 2001
L. Ashworth
Abstract: We studied the reproductive success and pollinators of Cucurbita maxima ssp. andreana in different disturbed habitats where it grows naturally. Data were obtained from three populations. One grew within a soybean crop, the other within a corn crop, and the third in an abandoned crop field. Cucurbita maxima ssp. andreana is an annual vine with a flowering period from December to April. Male flowers appear first, thereafter female and male flowers appear together. Flower lifetime (9 h) was similar in male and female flowers. The pollinator guild was comparable for the three populations but some differences in the frequency of the insect species were observed. Native bees were the main pollinators in the population in the abandoned field, while beetles pollinated the populations in crop fields. These differences were not linked with the pre-emergent reproductive success, fruit and seed set, or fruit quality. This is a self-compatible plant. Fruit and seed set and fruit traits (total mass, width and length of fruits, number of seeds per fruit, and seed mass) did not show significant differences between hand-cross and hand-self pollinated flowers. This wild cucurbit is a generalist with respect to pollinator guild, and flower visitors seem to be highly efficient in pollen transference. Cucurbita maxima ssp. andreana is well adapted to disturbed habitats because plants ripened fruits successfully, regardless of the group of insects visiting flowers. [source]

Interannual and interpopulation variation in Helichrysum stoechas (Asteraceae), a species of disturbed habitats in the Mediterranean region

PLANT SPECIES BIOLOGY, Issue 1 2001
Arnaud Martin
Abstract This study examines the interpopulation, interannual and individual variation in Helichrysum stoechas L., a perennial species that colonizes disturbed habitats in the Mediterranean region. The phenotypic variation in five populations was studied. Characters such as plant height and volume, numbers of capitula and flowers, weight of achenes and germination parameters were recorded in situ and in the laboratory for the same individuals for two consecutive years. The data were analyzed to examine the differences between populations and years compared to within-population variation. Results show that the germination rate, the average weight of achenes and the average number of capitula per stem varied considerably from one year to another, independently of population. This year-to-year variation suggests that these traits exhibit phenotypic plasticity. The substantial variation in precipitation during the 2 year study may account for the observed temporal variation. There was some weak correlations between the different characters studied within each population. Significant positive correlations were observed between mean achene weight and the total number of achenes produced per plant and with plant size. [source]

The impact of fallback foods on wild ring-tailed lemur biology: A comparison of intact and anthropogenically disturbed habitats

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 4 2009
Michelle L. Sauther
Abstract Fallback foods are often viewed as central in shaping primate morphology, and influencing adaptive shifts in hominin and other primate evolution. Here we argue that fruit of the tamarind tree (Tamarindus indica) qualifies as a fallback food of ring-tailed lemurs (Lemur catta) at the Beza Mahafaly Special Reserve (BMSR), Madagascar. Contrary to predictions that fallback foods may select for dental and masticatory morphologies adapted to processing these foods, consumption of tamarind fruit by these lemurs leaves a distinct pattern of dental pathology among ring-tailed lemurs at BMSR. Specifically, the physical and mechanical properties of tamarind fruit likely result in a high frequency of severe tooth wear, and subsequent antemortem tooth loss, in this lemur population. This pattern of dental pathology is amplified among lemurs living in disturbed areas at Beza Mahafaly, resulting from a disproportionate emphasis on challenging tamarind fruit, due to few other fruits being available. This is in part caused by a reduction in ground cover and other plants due to livestock grazing. As such, tamarind trees remain one of the few food resources in many areas. Dental pathologies are also associated with the use of a nonendemic leaf resource Argemone mexicana, an important food during the latter part of the dry season when overall food availability is reduced. Such dental pathologies at Beza Mahafaly, resulting from the use or overemphasis of fallback foods for which they are not biologically adapted, indicate that anthropogenic factors must be considered when examining fallback foods. Am J Phys Anthropol 140:671,686, 2009. © 2009 Wiley-Liss, Inc. [source]

A Method for Evaluating Outcomes of Restoration When No Reference Sites Exist

RESTORATION ECOLOGY, Issue 1 2009
J. Stephen Brewer
Abstract Ecological restoration typically seeks to shift species composition toward that of existing reference sites. Yet, comparing the assemblages in restored and reference habitats assumes that similarity to the reference habitat is the optimal outcome of restoration and does not provide a perspective on regionally rare off-site species. When no such reference assemblages of species exist, an accurate assessment of the habitat affinities of species is crucial. We present a method for using a species by habitat data matrix generated by biodiversity surveys to evaluate community responses to habitat restoration treatments. Habitats within the region are rated on their community similarity to a hypothetical restored habitat, other habitats of conservation concern, and disturbed habitats. Similarity scores are reinserted into the species by habitat matrix to produce indicator (I) scores for each species in relation to these habitats. We apply this procedure to an open woodland restoration project in north Mississippi (U.S.A.) by evaluating initial plant community responses to restoration. Results showed a substantial increase in open woodland indicators, a modest decrease in generalists historically restricted to floodplain forests, and no significant change in disturbance indicators as a group. These responses can be interpreted as a desirable outcome, regardless of whether species composition approaches that of reference sites. The broader value of this approach is that it provides a flexible and objective means of predicting and evaluating the outcome of restoration projects involving any group of species in any region, provided there is a biodiversity database that includes habitat and location information. [source]

Responses of tropical rainforest birds to abandoned plantations, edges and logged forest in the Western Ghats, India

ANIMAL CONSERVATION, Issue 3 2002
T. R. Shankar Raman
This study examined the effects of alteration of tropical rainforest vegetation structure and composition on bird community structure and the influence of life-history traits on species persistence in the Kalakad-Mundanthurai Tiger Reserve, Western Ghats. Systematic sampling for vegetation and point count surveys for birds were carried out in cardamom plantations abandoned for 5 and 15 years, plantation-rainforest edges, a selectively logged forest patch and adjoining undisturbed rainforest sites. Principal components analysis of vegetation variables revealed clear differences between undisturbed and altered sites in woody plant and cane densities, canopy cover and vertical stratification. Bird species richness was lowest in cardamom plantations abandoned for 5 years and highest in logged and undisturbed forest. Bird species richness and similarity with undisturbed forest were significantly positively related to the vegetation component representing woody plant and cane (Calamus spp.) densities. Sites that were more similar in tree species composition had more similar bird communities whereas similarity in foliage profile between sites did not influence bird community similarity. Birds that were rare, were large-bodied and belonged to the carnivore, omnivore, bark-surface feeder and terrestrial insectivore guilds were adversely affected by habitat alteration. Restoring woody plant and cane densities and rainforest floristic composition in disturbed habitats may be required for management and conservation of bird communities typical to the region. [source]

The relationship between soil seed bank, above-ground vegetation and disturbance intensity on old-field successional permanent plots

APPLIED VEGETATION SCIENCE, Issue 4 2009
Michaela Dölle
Abstract Questions: How does disturbance and successional age influence richness, size and composition of the soil seed bank? What is the potential contribution of the soil seed bank to the plant community composition on sites differing in their successional age or disturbance intensity? Location: Experimental Botanical Garden of Göttingen University, central Germany. Methods: Above-ground vegetation and soil seed bank were studied on formerly arable fields in a 36-year-old permanent plot study with five disturbance intensities, ranging from yearly ploughing via mowing to long-term uninterrupted succession. We compared species compositions, seed densities and functional features of the seed bank and above-ground vegetation by using several methods in parallel. Results: The seed bank was mainly composed of early successional species typical of strongly disturbed habitats. The difference between seed bank composition and above-ground vegetation decreased with increasing disturbance intensity. The species of greatest quantitative importance in the seed bank was the non-native forb Solidago canadensis. Conclusions: The ability of a plant community to regenerate from the soil seed bank dramatically decreases with increasing time since abandonment (successional age) and with decreasing disturbance intensity. The present study underlines that plant species typical of grasslands and woodlands are limited by dispersal capacity, owing to low capacity for accumulation of seeds in the soil and the fact that most species do not build up persistent seed banks. Rare and target species were almost absent from the seed bank and will, after local elimination, depend on reintroduction for continuation of their presence. [source]

Lessons from primary succession for restoration of severely damaged habitats

APPLIED VEGETATION SCIENCE, Issue 1 2009
Lawrence R. Walker
Abstract Questions: How can studies of primary plant succession increase the effectiveness of restoration activities? Can restoration methods be improved to contribute to our understanding of succession? Results: Successional studies benefit restoration in six areas: site amelioration, development of community structure, nutrient dynamics, species life history traits, species interactions, and modeling of transitions and trajectories. Primary succession provides valuable lessons for understanding temporal dynamics through direct, long-term observations on severely disturbed habitats. These lessons assist restoration efforts on infertile or even toxic substrates. Restoration that uses scientific protocols (e.g., control treatments and peer-reviewed publications) can offer insights into successional processes. Conclusions: A century of studying successional dynamics has provided modern restoration activities with many useful lessons that are not being fully utilized. [source]

Low population differentiation and high genetic diversity in the invasive species Carduus acanthoides L. (Asteraceae) within its native range in the Czech Republic

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2009
BOHUMIL MANDÁK
Colonizing species are predicted to suffer from reductions in genetic diversity during founding events. Although there is no unique mode of reproduction that is characteristic of successful plant colonizers, many of them are predominantly self-fertilizing or apomictic species, and almost all outcrossing colonizers are self-compatible. Carduus acanthoides comprises a species of disturbed habitats with wind-dispersed seeds that colonizes open spaces of various sizes. Population genetic diversity was expressed by assessing patterns of variation at nine putatively neutral allozyme loci within and among 20 natural populations in its native distribution range in the Czech Republic. Overall, C. acanthoides displayed high levels of genetic diversity compared to other herbaceous plants. The percentage of polymorphic loci was 84.5, with values of 2.37, 0.330, and 0.364 for the mean number of alleles per polymorphic locus (A), observed heterozygosity (Ho), and expected heterozygosity (He), respectively. There was only weak evidence of inbreeding within populations (f = 0.097) and very low genetic differentiation among populations (, = 0.085). Analyses of the data provide strong evidence for isolation-by-distance for the whole study area. Even the colonizing species, C. acanthoides, currently supports a substantial amount of allozyme variation at both the species and population levels. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 596,607. [source]

Temporal patterns of geographic parthenogenesis in a freshwater snail

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2007
FRIDA BEN-AMI
Geographic parthenogenesis describes the observation that parthenogenetic organisms tend to occupy environments different from those of their close, sexually reproducing relatives. These environments are often described as extreme or disturbed habitats. We examined whether patterns of geographical parthenogenesis persist over time, by conducting a 3-year life-history survey and comparing two very proximate habitats of the freshwater snail Melanoides tuberculata: Nahal Arugot, a desert stream naturally disturbed by flash floods, and Or Ilan, a stable freshwater pond. Both sites occur in a xeric environment and are subject to otherwise similar biotic (e.g. parasites, predators) and climatic conditions. In the stable habitat, male frequencies and snail densities were significantly higher than in the disturbed one, whereas infection levels, mean embryo counts, and water temperatures were similar at both sites. Additionally, male frequencies declined after density decreased, thereby providing evidence for geographical parthenogenesis via reproductive assurance. Infection prevalence was very low regardless of reproduction mode. Although further genetic work is required, the apparent metapopulation structure of M. tuberculata in the Judean desert may be suitable for evaluating other possible explanations of geographical parthenogenesis. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 91, 711,718. [source]

Reproduction in Wild Populations of the Threatened Tree Macadamia tetraphylla: Interpopulation Pollen Enriches Fecundity in a Declining Species

BIOTROPICA, Issue 3 2009
Philip C. Pisanu
ABSTRACT Macadamia tetraphylla is a subtropical rain forest tree from fragmented lowlands in eastern Australia. Owing to habitat loss and fragmentation, this commercially important species is vulnerable to extinction. Breeding system and fecundity were investigated in nine populations incorporating three habitat types (moderately disturbed, highly disturbed, and intact) to determine if seed set, seed weight, and genetic diversity are compromised by disturbance. Breeding success was also tested using pollen donors from distant (30,100 km), local (2,3 km), neighbor (10,20 m), and near-neighbor (< 10 m) sources. Macadamia tetraphylla is weakly self-compatible but incapable of automatic self-pollination. Across populations, seed to flower ratios were always < 0.1 percent in open-pollinated trees and trees from moderately disturbed habitats had the highest fruit production. Outcross pollen produced more seed per raceme than open-pollinated or self-pollination treatments. Seed set and seed weights were positively influenced by pollen source with local pollen and distant pollen effecting more or heavier seeds. Germination rates and genetic diversity did not vary significantly in seedlings from different pollen sources. Results suggest a pollen source from at least a 2 km distance is an optimal outbreeding distance; however, many wild populations do not have conspecifics at optimal distances owing to habitat fragmentation. Highly disturbed populations are producing seed but the longevity of these sites is threatened by weed invasions. We conclude that small populations in degraded habitats that are at risk of being overlooked should not be ignored but should be a focus for restoration efforts as they are a valuable asset for the conservation of M. tetraphylla. [source]