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Habitat Area (habitat + area)
Selected AbstractsEstimating population size and habitat associations of two federally endangered mussels in the St. Croix River, Minnesota and Wisconsin, USA,AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 3 2010Daniel J. Hornbach Abstract 1.North America is a globally important centre of freshwater mussel biodiversity. Accurate population estimates and descriptions of critical habitat for endangered species of mussels are needed but are hindered by their patchy distribution and the dynamic nature of their habitat. Adaptive cluster sampling (ACS) was used to estimate population size and habitat associations of two federally endangered species, Higgins eye (Lampsilis higginsii) and winged mapleleaf (Quadrula fragosa), in the St. Croix River. 2.This river holds the largest known winged mapleleaf population in the upper Mississippi River and contains Essential Habitat Areas for Higgins eye. Winged mapleleaf density ranged from 0.008,0.020 individuals m,2 (coefficient of variation=50,66%), yielding an estimate of 13 000 winged mapleleaf in this reach of the river. Higgins eye density varied from 0.008,0.015 individuals m,2 (coefficient of variation=66,167%) giving an estimate of 14 400 individuals in this area. 3.Higgins eye and winged mapleleaf were associated with areas of the overall highest mussel density and species richness, suggesting these endangered species occur in ,premier' mussel habitat. There were no differences in many microhabitat factors for sites with and without either endangered species. Select hydraulic measures (such as shear velocity and shear stress) showed significant differences in areas with and without the winged mapleleaf but not for Higgins eye. Areas that are less depositional support dense and diverse mussel assemblages that include both endangered species, with winged mapleleaf having a narrower habitat range than Higgins eye. 4.This study suggests that ACS can provide statistically robust estimates of density with 2,3 times more efficiency than simple random sampling. ACS, however, was quite time consuming. This work confirmed that of others demonstrating that larger-scale hydraulic parameters might be better predictors of prime mussel habitat than fine-scaled microhabitat factors. Using hydraulic measures may allow improved identification of potentially critical mussel habitat. Copyright © 2009 John Wiley & Sons, Ltd. [source] Extinction debt on oceanic islandsECOGRAPHY, Issue 2 2010Kostas A. Triantis Habitat destruction is the leading cause of species extinctions. However, there is typically a time-lag between the reduction in habitat area and the eventual disappearance of the remnant populations. These "surviving but ultimately doomed" species represent an extinction debt. Calculating the magnitude of such future extinction events has been hampered by potentially inaccurate assumptions about the slope of species,area relationships, which are habitat- and taxon-specific. We overcome this challenge by applying a method that uses the historical sequence of deforestation in the Azorean Islands, to calculate realistic and ecologically-adjusted species,area relationships. The results reveal dramatic and hitherto unrecognized levels of extinction debt, as a result of the extensive destruction of the native forest:>95%, in<600,yr. Our estimations suggest that more than half of the extant forest arthropod species, which have evolved in and are dependent on the native forest, might eventually be driven to extinction. Data on species abundances from Graciosa Island, where only a very small patch of secondary native vegetation still exists, as well as the number of species that have not been found in the last 45,yr, despite the extensive sampling effort, offer support to the predictions made. We argue that immediate action to restore and expand native forest habitat is required to avert the loss of numerous endemic species in the near future. [source] The area requirements of an ecosystem service: crop pollination by native bee communities in CaliforniaECOLOGY LETTERS, Issue 11 2004Claire Kremen Abstract Managing ecosystem services is critical to human survival, yet we do not know how large natural areas must be to support these services. We investigated how crop pollination services provided by native, unmanaged, bee communities varied on organic and conventional farms situated along a gradient of isolation from natural habitat. Pollination services from native bees were significantly, positively related to the proportion of upland natural habitat in the vicinity of farm sites, but not to any other factor studied, including farm type, insecticide usage, field size and honeybee abundance. The scale of this relationship matched bee foraging ranges. Stability and predictability of pollination services also increased with increasing natural habitat area. This strong relationship between natural habitat area and pollination services was robust over space and time, allowing prediction of the area needed to produce a given level of pollination services by wild bees within this landscape. [source] Effects of mute swan grazing on a keystone macrophyteFRESHWATER BIOLOGY, Issue 12 2007MATTHEW T. O'HARE Summary 1. This study describes the early summer foraging behaviour of mute swans (Cygnus olor) on the River Frome, a highly productive chalk stream in southern England in which Ranunculus penicillatus pseudofluitans is the dominant macrophyte. 2. A daily maximum of 41 ± 2.5 swans were present along the 1.1 km study reach during the study period (late May to the end of June). The river was the primary feeding habitat. Feeding activity on the river at dawn and dusk was much lower than during daylight, but we cannot rule out the possibility that swans fed during the hours of darkness. 3. The effects of herbivory on R. pseudofluitans biomass and morphology were quantified. Biomass was lower in grazed areas and swans grazed selectively on leaves in preference to stems. A lower proportion of stems from grazed areas possessed intact stem apices and flowering of the plant was reduced in grazed areas. 4. A model, based on the swans' daily consumption, was used to predict the grazing pressure of swans on R. pseudofluitans. The model accurately predicted the number of bird days supported by the study site, only if grazing was assumed to severely reduce R. pseudofluitans growth. The proportion of the initial R. pseudofluitans biomass consumed by a fixed number of swans was predicted to be greater when the habitat area was smaller, initial R. pseudofluitans biomass was lower and R. pseudofluitans was of lower food value. 5. We concluded that the flux of N and P through the study reach was largely unaffected by swan activity. The quality of R. pseudofluitans mesohabitat (the plant as habitat for invertebrates and fish) was significantly reduced by grazing which also indirectly contributed to reduced roughness (Manning's n) and by inference water depth. Wetted habitat area for fish and invertebrates would also be lowered over the summer period as a consequence of the reduction in water depth. It was estimated that, while grazing, an individual swan may eat the same mass of invertebrates per day as a 300-g trout. 6. There is a need to manage the conflict between mute swans and the keystone macrophyte, R. pseudofluitans, in chalk streams, and the modelling approach used here offers a potentially useful tool for this purpose. [source] Influences of habitat complexity on the diversity and abundance of epiphytic invertebrates on plantsFRESHWATER BIOLOGY, Issue 4 2003Hiromi Taniguchi SUMMARY 1. The compound influence of habitat complexity and patch size on stream invertebrate assemblages associated with submerged macrophytes was investigated through field sampling of two natural macrophyte species with contrasting leaf morphologies (complex, Ranunculus yezoensis; simple, Sparganium emersum) and an experiment with two artificial plants with different levels of morphological complexity. 2. The artificial plant experiment was designed to separate the effects of habitat area (patch size) and habitat complexity, thus enabling a more rigorous assessment of complexity per se than in previous studies where only a single patch size was used. Simple and complex artificial plants were established with five different patch sizes corresponding to the range found in natural plants. 3. Invertebrates occurred on both complex and simple forms of natural and artificial plants at similar abundances with dipterans and ephemeropterans being predominant. Taxon richness was higher on structurally complex Ranunculus than on simple Sparganium and was similarly higher on the complex artificial plant than on the simple one, over the entire range of habitat patch sizes. Thus, architectural complexity affected the taxon richness of epiphytic invertebrates, independently of habitat scale. 4. On the natural plants there was no difference in the abundance (both number of individuals and biomass) of invertebrates between simple and complex forms, while on artificial plants more invertebrates occurred on complex than on simple forms. The amount of particulate organic matter, >225 ,m (POM) and chlorophyll a showed mixed patterns on natural and artificial plants, suggesting that the availability of these resources is not an overriding proximate factor controlling invertebrate abundance on plants. The difficulty of extrapolating from experimental results involving use of artificial plants is discussed, especially when considering the relationship between habitat structure and the occurrence of epiphytic invertebrates on natural plants. [source] When the prairie varies: the importance of site characteristics for strategising insect conservationINSECT CONSERVATION AND DIVERSITY, Issue 4 2009CHRIS LOONEY Abstract., 1.,The bunchgrass prairies of the Palouse region in eastern Washington state and adjacent Idaho have been mostly converted to agriculture in the past century. Prairie habitat currently exists only on small remnants scattered across the landscape. 2.,The invertebrate fauna of these habitat remnants is poorly known, both in terms of species diversity and community composition. 3.,Baited pitfall traps were used to sample carrion-attracted beetles during June and July of 2003 from high-quality prairie remnants of varying size and soil characteristics. 4.,Twenty-three beetle species in five families were found. Species richness and Shannon-Wiener diversity were not significantly correlated with habitat area or perimeter,area ratio. 5.,Beetle abundance and community structure were strongly correlated with soil characteristics. Deeper, loessal soils had greater overall beetle abundance than shallower, rocky soils, although some species were more frequently captured in shallower, rocky soil sites. 6.,Conservation plans emphasising only remnant size and condition do not sufficiently capture variability in insect communities across Palouse prairie remnants. [source] Predator size, prey size and threshold food densities of diving ducks: does a common prey base support fewer large animals?JOURNAL OF ANIMAL ECOLOGY, Issue 5 2009Samantha E. Richman Summary 1. Allometry predicts that a given habitat area or common prey biomass supports fewer numbers of larger than smaller predators; however, birds from related taxa or the same feeding guild often deviate from this pattern. In particular, foraging costs of birds may differ among locomotor modes, while intake rates vary with accessibility, handling times and energy content of different-sized prey. Such mechanisms might affect threshold prey densities needed for energy balance, and thus relative numbers of different-sized predators in habitats with varying prey patches. 2. We compared the foraging profitability (energy gain minus cost) of two diving ducks: smaller lesser scaup (Aythya affinis, 450,1090 g) and larger white-winged scoters (Melanitta fusca, 950,1800 g). Calculations were based on past measurements of dive costs with respirometry, and of intake rates of a common bivalve prey ranging in size, energy content and burial depth in sediments. 3. For scaup feeding on small prey <12 mm long, all clams buried deeper than 5 cm were unprofitable at realistic prey densities. For clams buried in the top 5 cm, the profitability threshold decreased from 216 to 34 clams m,2 as energy content increased from 50 to 300 J clam,1. 4. For larger scoters feeding on larger prey 18,24 mm long, foraging was profitable for clams buried deeper than 5 cm, with a threshold density of 147 m,2 for clams containing 380 J clam,1. For clams <5 cm deep, the threshold density decreased from 86 to 36 clams m,2 as energy content increased from 380 to 850 J clam,1. If scoters decreased dive costs by swimming with wings as well as feet (not an option for scaup), threshold prey densities were 11,12% lower. 5. Our results show that threshold densities of total prey numbers for different-sized ducks depend on prey size structure and depth in the sediments. Thus, heterogeneity in disturbance regimes and prey population dynamics can create a mosaic of patches favouring large or small predators. Whether a given area or total prey biomass will support greater numbers of larger or smaller predators will vary with these effects. [source] Effects of ecogeographic variables on genetic variation in montane mammals: implications for conservation in a global warming scenarioJOURNAL OF BIOGEOGRAPHY, Issue 7 2007Amy M. Ditto Abstract Aim, Evolutionary theory predicts that levels of genetic variation in island populations will be positively correlated with island area and negatively correlated with island isolation. These patterns have been empirically established for oceanic islands, but little is known about the determinants of variation on habitat islands. The goals of this study were twofold. Our first aim was to test whether published patterns of genetic variation in mammals occurring on montane habitat islands in the American Southwest conformed to expectations based on evolutionary theory. The second aim of this research was to develop simple heuristic models to predict changes in genetic variation that may occur in these populations as a result of reductions in available mountaintop habitat in response to global warming. Location, Habitat islands of conifer forest on mountaintops in the American Southwest. Methods, Relationships between island area and isolation with measures of allozyme variation in four species of small mammal, namely the least chipmunk (Tamias minimus), Colorado chipmunk (Tamias quadrivittatus), red squirrel (Tamiasciurus hudsonicus), and Mexican woodrat (Neotoma mexicana), were determined using correlation and regression techniques. Significant relationships between island area and genetic variation were used to develop three distinct statistical models with which to predict changes in genetic variation following reduction in insular habitat area arising from global warming. Results, Patterns of genetic variation in each species conformed to evolutionary predictions. In general, island area was the most important determinant of heterozygosity, while island isolation was the most important determinant of polymorphism and allelic diversity. The heuristic models predicted widespread reductions in genetic variation, the extent of which depended on the population and model considered. Main conclusions, The results support a generalized pattern of genetic variation for any species with an insular distribution, with reduced variation in smaller, more isolated populations. We predict widespread reductions in genetic variation in isolated populations of montane small mammals in the American Southwest as a result of global warming. We conclude that climate-induced reductions in the various dimensions of genetic variation may increase the probability of population extinction in both the short and long term. [source] Patterns and determinants of shorebird species richness in the circumpolar ArcticJOURNAL OF BIOGEOGRAPHY, Issue 3 2005Sara S. Henningsson Abstract Aim, The intention with this study was first to investigate and describe the broad-scale geographical patterns of species richness of breeding shorebirds (Charadriiformes; families: Charadriidae, Scolopacidae and Haematopodidae) throughout the arctic tundra biome. Secondly, after compensating for the positive relationship between net primary productivity (NPP) and species richness, the relative importance of additional ecological and historical variables for species richness was investigated. The main variables considered are NPP, length of snow- and ice-free season, accessibility of regions depending on migratory flyway systems, tundra area at Pleistocene (120 and 20,18 ka bp) and Holocene (8 ka bp) times, and tundra area at present. Methods, Information on shorebird species breeding distributions was compiled from distribution atlases and species accounts. The breeding distributions of shorebirds with ranges partly or completely in the Arctic (a total of 50 species) were mapped in ArcView 3.2 to create a raster grid layer of shorebird species richness at a 1° latitude × longitude resolution. The total and mean species richness value was calculated per each 10° of longitude sector of the Arctic. The relationships between species richness and the different climatic and environmental variables were analysed on the basis of this sector-wise division of the arctic tundra. The influence of each variable on species richness was investigated using univariate and multivariate analyses (multivariate linear regression and general linear model). Results, We found that patterns of breeding shorebird species richness in the Arctic tundra biome are to a large degree determined by the NPP, the length of the snow- or ice-free season, the diversity of migratory flyways, as well as the historical extent of tundra habitat area during the maximum cooling of the last glacial period. Essentially, two main regions are distinguishable in the circumpolar Arctic regarding shorebird community richness. These are a species-rich Beringia-centred region and a species-poor Atlantic-centred region. Main conclusions, The underlying explanations to these major trends may primarily be attributed to factors that operate at present through accessibility of areas from contemporary migration flyways, as well as processes that operated in the past during and after the last glacial cycle. The most prominent influence on the shorebird diversity was found for NPP in combination with the diversity of migratory flyways. These flyways provide the links between breeding and wintering resources, often separated by huge distances, and the geographical and ecological conditions associated with the shorebirds' migration seem to be of particular importance for their breeding diversity in different sectors of circumpolar tundra. [source] Plant functional group composition and large-scale species richness in European agricultural landscapesJOURNAL OF VEGETATION SCIENCE, Issue 1 2008Jaan Liira Abstract Question: Which are the plant functional groups responding most clearly to agricultural disturbances? Which are the relative roles of habitat availability, landscape configuration and agricultural land use intensity in affecting the functional composition and diversity of vascular plants in agricultural landscapes? Location: 25 agricultural landscape areas in seven European countries. Methods: We examined the plant species richness and abundance in 4 km × 4 km landscape study sites. The plant functional group classification was derived from the BIOLFLOR database. Factorial decomposition of functional groups was applied. Results: Natural habitat availability and low land use intensity supported the abundance and richness of perennials, sedges, pteridophytes and high nature quality indicator species. The abundance of clonal species, C and S strategists was also correlated with habitat area. An increasing density of field edges explained a decrease in richness of high nature quality species and an increase in richness of annual graminoids. Intensive agriculture enhanced the richness of annuals and low nature quality species. Conclusions: Habitat patch availability and habitat quality are the main drivers of functional group composition and plant species richness in European agricultural landscapes. Linear elements do not compensate for the loss of habitats, as they mostly support disturbance tolerant generalist species. In order to conserve vascular plant species diversity in agricultural landscapes, the protection and enlargement of existing patches of (semi-) natural habitats appears to be more effective than relying on the rescue effect of linear elements. This should be done in combination with appropriate agricultural management techniques to limit the effect of agrochemicals to the fields. [source] Transport and environmental temperature variability of eggs and larvae of the Japanese anchovy (Engraulis japonicus) and Japanese sardine (Sardinops melanostictus) in the western North Pacific estimated via numerical particle-tracking experimentsFISHERIES OCEANOGRAPHY, Issue 2 2009SACHIHIKO ITOH Abstract Numerical particle-tracking experiments were performed to investigate the transport and variability in environmental temperature experienced by eggs and larvae of Pacific stocks of the Japanese anchovy (Engraulis japonicus) and Japanese sardine (Sardinops melanostictus) using high-resolution outputs of the Ocean General Circulation Model for the Earth Simulator (OFES) and the observed distributions of eggs collected from 1978 to 2004. The modeled anchovy individuals tend to be trapped in coastal waters or transported to the Kuroshio,Oyashio transition region. In contrast, a large proportion of the sardines are transported to the Kuroshio Extension. The egg density-weighted mean environmental temperature until day 30 of the experiment was 20,24°C for the anchovy and 17,20°C for the sardine, which can be explained by spawning areas and seasons, and interannual oceanic variability. Regression analyses revealed that the contribution of environmental temperature to the logarithm of recruitment per spawning (expected to have a negative relationship with the mean mortality coefficient) was significant for both the anchovy and sardine, especially until day 30, which can be regarded as the initial stages of their life cycles. The relationship was quadratic for the anchovy, with an optimal temperature of 21,22°C, and linear for the sardine, with a negative coefficient. Differences in habitat areas and temperature responses between the sardine and anchovy are suggested to be important factors in controlling the dramatic out-of-phase fluctuations of these species. [source] Regionalization of methane emissions in the Amazon Basin with microwave remote sensingGLOBAL CHANGE BIOLOGY, Issue 5 2004John M. Melack Abstract Wetlands of the Amazon River basin are globally significant sources of atmospheric methane. Satellite remote sensing (passive and active microwave) of the temporally varying extent of inundation and vegetation was combined with field measurements to calculate regional rates of methane emission for Amazonian wetlands. Monthly inundation areas for the fringing floodplains of the mainstem Solimões/Amazon River were derived from analysis of the 37 GHz polarization difference observed by the Scanning Multichannel Microwave Radiometer from 1979 to 1987. L-band synthetic aperture radar data (Japanese Earth Resources Satellite-1) were used to determine inundation and wetland vegetation for the Amazon basin (<500 m elevation) at high (May,June 1996) and low water (October 1995). An extensive set of measurements of methane emission is available from the literature for the fringing floodplains of the central Amazon, segregated into open water, flooded forest and floating macrophyte habitats. Uncertainties in the regional emission rates were determined by Monte Carlo error analyses that combined error estimates for the measurements of emission and for calculations of inundation and habitat areas. The mainstem Solimões/Amazon floodplain (54,70°W) emitted methane at a mean annual rate of 1.3 Tg C yr,1, with a standard deviation (SD) of the mean of 0.3 Tg C yr,1; 67% of this range in uncertainty is owed to the range in rates of methane emission and 33% is owed to uncertainty in the areal estimates of inundation and vegetative cover. Methane emission from a 1.77 million square kilometers area in the central basin had a mean of 6.8 Tg C yr,1 with a SD of 1.3 Tg C yr,1. If extrapolated to the whole basin below the 500 m contour, approximately 22 Tg C yr,1 is emitted; this mean flux has a greenhouse warming potential of about 0.5 Pg C as CO2. Improvement of these regional estimates will require many more field measurements of methane emission, further examination of remotely sensed data for types of wetlands not represented in the central basin, and process-based models of methane production and emission. [source] Assemblages of soil macrofauna across a Scottish land-use intensification gradient: influences of habitat quality, heterogeneity and areaJOURNAL OF APPLIED ECOLOGY, Issue 6 2005PAUL EGGLETON Summary 1Land-use intensification strongly influences biodiversity by altering habitat heterogeneity, the distribution of habitat types and their extent. This study explores these effects within mixed semi-natural/agricultural mosaic habitats in Scotland, examining the effect of land-use intensification on the soil macrofauna at point (m2), landscape (km2) and regional (> 1 km2) scales. 2The soil macrofauna in six 1-km2 sampling areas (land-use units; LUU) were sampled using a combined hand-sorting and Winkler bag extraction technique. Within each LUU, 16 1-m2 samples were taken in each of 2 successive years. Each LUU had a mixture of land-use types, representing an agricultural intensification gradient. 3The following hypotheses were tested: (i) the study area sustains a number of distinct habitats as defined by soil macrofaunal composition; (ii) a greater number of restricted range species are found in semi-natural habitats; (iii) local (point) species density is related to habitat type; (iv) overall levels of species richness per habitat at regional scales are related to species-area effects; and (v) landscape-level species density is correlated with habitat heterogeneity. 4Initial analysis revealed five distinct habitat types: Caledonian forest (semi-natural pine forest), closed canopy woodland (pine plantation and broadleaved woodland), riparian habitats (wet woodland and grassland), pasture (improved grassland) and arable (crop fields). 5As hypothesized, the Caledonian habitat contained a greater number of restricted-range species than the other habitats. However, conifer plantations contained more restricted range species than expected, given their anthropogenic origin. Species density per m2 was most strongly affected by habitat type. At the regional level, the size of the species pool was correlated with the size of habitat areas. There were more species overall in LUU with greater habitat heterogeneity. 6Synthesis and applications. Caledonian pine forests have high species densities and contain species of conservation value. Mixed conifer plantations also appear to have a surprisingly high invertebrate conservation value. In contrast, intensively managed agricultural habitats have low species densities and conservation value. Generally, mixed land-use areas have higher species densities than single land-use areas. This emphasizes the need for careful management of forest systems within the matrix of agricultural habitats to maximize landscape diversity. [source] | |||||||||||||