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Distinct Habitat Types (distinct + habitat_type)
Selected AbstractsThe effects of fire, local environment and time on ant assemblages in fens and forestsDIVERSITY AND DISTRIBUTIONS, Issue 6 2005Jaime S. Ratchford ABSTRACT We investigated the effects of the abiotic environment, plant community composition and disturbance by fire on ant assemblages in two distinct habitat types in the Siskiyou Mountains in northern California and southern Oregon, USA. Sampling over 2 years in burned and unburned Darlingtonia fens and their adjacent upland forests, we found that the effects of disturbance by fire depended on habitat type. In forests, fire intensity predicted richness in ant assemblages in both years after the fire, and plant community composition predicted richness 2 years after the fire. No factors were associated with richness in the species-poor fen ant assemblages. Species-specific responses to both habitat type and disturbance by fire were idiosyncratic. Assemblage composition depended on habitat type, but not disturbance by fire, and the composition of each assemblage between years was more dissimilar in burned than unburned sites. [source] Optimizing dispersal and corridor models using landscape geneticsJOURNAL OF APPLIED ECOLOGY, Issue 4 2007CLINTON W. EPPS Summary 1Better tools are needed to predict population connectivity in complex landscapes. ,Least-cost modelling' is one commonly employed approach in which dispersal costs are assigned to distinct habitat types and the least-costly dispersal paths among habitat patches are calculated using a geographical information system (GIS). Because adequate data on dispersal are usually lacking, dispersal costs are often assigned solely from expert opinion. Spatially explicit, high-resolution genetic data may be used to infer variation in animal movements. We employ such an approach to estimate habitat-specific migration rates and to develop least-cost connectivity models for desert bighorn sheep Ovis canadensis nelsoni. 2Bighorn sheep dispersal is thought to be affected by distance and topography. We incorporated both factors into least-cost GIS models with different parameter values and estimated effective geographical distances among 26 populations. We assessed which model was correlated most strongly with gene flow estimates among those populations, while controlling for the effect of anthropogenic barriers. We used the best-fitting model to (i) determine whether migration rates are higher over sloped terrain than flat terrain; (ii) predict probable movement corridors; (iii) predict which populations are connected by migration; and (iv) investigate how anthropogenic barriers and translocated populations have affected landscape connectivity. 3Migration models were correlated most strongly with migration when areas of at least 10% slope had 1/10th the cost of areas of lower slope; thus, gene flow occurred over longer distances when ,escape terrain' was available. Optimal parameter values were consistent across two measures of gene flow and three methods for defining population polygons. 4Anthropogenic barriers disrupted numerous corridors predicted to be high-use dispersal routes, indicating priority areas for mitigation. However, population translocations have restored high-use dispersal routes in several other areas. Known intermountain movements of bighorn sheep were largely consistent with predicted corridors. 5Synthesis and applications. Population genetic data provided sufficient resolution to infer how landscape features influenced the behaviour of dispersing desert bighorn sheep. Anthropogenic barriers that block high-use dispersal corridors should be mitigated, but population translocations may help maintain connectivity. We conclude that developing least-cost models from similar empirical data could significantly improve the utility of these tools. [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] Intimately linked or hardly speaking?MOLECULAR ECOLOGY, Issue 3 2001The relationship between genotype, environmental gradients in a Louisiana Iris hybrid population Abstract Several models of hybrid zone evolution predict the same spatial patterns of genotypic distribution whether or not structuring is due to environment-dependent or -independent selection. In this study, we tested for evidence of environment-dependent selection in an Iris fulva×Iris brevicaulis hybrid population by examining the distribution of genotypes in relation to environmental gradients. We selected 201 Louisiana Iris plants from within a known hybrid population (80 m × 80 m) and placed them in four different genotypic classes (I. fulva, I. fulva -like hybrid, I. brevicaulis -like hybrid and I. brevicaulis) based on seven species-specific random amplified polymorphic DNA (RAPD) markers and two chloroplast DNA haplotypes. Environmental variables were then measured. These variables included percentage cover by tree canopy, elevation from the high water mark, soil pH and percentage soil organic matter. Each variable was sampled for all 201 plants. Canonical discriminant analysis (CDA) was used to infer the environmental factors most strongly associated with the different genotypic groups. Slight differences in elevation (,0.5 m to +0.4 m) were important for distinguishing habitat distributions described by CDA, even though there were no statistical differences between mean elevations alone. I. brevicaulis occurred in a broad range of habitats, while I. fulva had a narrower distribution. Of all the possible combinations, I. fulva -like hybrids and I. brevicaulis -like hybrids occurred in the most distinct habitat types relative to one another. Each hybrid class was not significantly different from its closest parent with regard to habitat occupied, but was statistically unique from its more distant parental species. Within the hybrid genotypes, most, but not all, RAPD loci were individually correlated with environmental variables. This study suggests that, at a very fine spatial scale, environment-dependent selection contributed to the genetic structuring of this hybrid zone. [source] Seasonal variations in black-faced black spider monkey (Ateles chamek) habitat use and ranging behavior in a southern Amazonian tropical forestAMERICAN JOURNAL OF PRIMATOLOGY, Issue 4 2006Robert B. Wallace Abstract Data are presented regarding the habitat use and ranging behavior of a spider monkey (Ateles chamek) community at Lago Caiman in northeastern Bolivia. Habitat use was driven primarily by fruit availability and distribution across the community home range. Strong seasonal variations occurred in fruit availability within all five of the floristically and phenologically distinct habitat types identified within the study site, and the spider monkeys dramatically shifted their ranging according to which habitat was richest in fleshy fruits. This use of local habitat diversity resulted in an unusually elongated shape for the home range that was otherwise typical of previous Ateles studies in terms of size. Ranging behavior was clumped and community core areas shifted seasonally across the focal community home range. Individual core areas were not relevant to the study due to dramatic community-wide shifts in ranging patterns. Day journey lengths were highly variable (460,5,690,m) and the distribution and abundance of fleshy fruit resources explained 81% of the monthly variations in mean day journey length. Keystone habitats for forest frugivores are identified and results are discussed with reference to previous studies on this genus, and the importance of considering keystone habitats and local habitat diversity within the management of forestry concessions in the region. Results are also discussed with reference to the behavioral ecology of the genus Ateles. Am. J. Primatol. 68:313,332, 2006. © 2006 Wiley-Liss, Inc. [source] Freshwater mussel assemblage structure in a regulated river in the Lower Mississippi River Alluvial Basin, USA,AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 1 2007Wendell R. Haag Abstract 1.This paper documents a diverse, reproducing freshwater mussel community (20 species) in Lower Lake , an impounded, regulated portion of the Little Tallahatchie River below Sardis Dam in Panola Co., Mississippi, USA. 2.Despite being regulated and impounded, the lake has a heterogeneous array of habitats that differ markedly in mussel community attributes. Four distinct habitat types were identified based on current velocity and substrate characteristics, representing a gradient from habitats having lotic characteristics to lentic habitats. All four habitat types supported mussels, but habitats most resembling unimpounded, lotic situations (relatively higher current velocity and coarser substrate) had the highest mussel abundance and species density (10.1 mussels m,2, 1.8 species m,2, respectively). Lentic habitats (no flow, fine substrate) were characterized by lower abundance and species density (2.0 mussels m,2, 0.8 species m,2, respectively), but supported mussel assemblages distinctive from lotic habitats. 3.Evidence of strong recent recruitment was observed for most species in the lake and was observed in all four habitat types. 4.Although impounded and regulated, Lower Lake represents one of the few areas of stable large-stream habitat in the region. The presence of a diverse, healthy mussel community in this highly modified habitat suggests that a large component of the regional mussel fauna is relatively resilient and adaptable and is limited primarily by the absence of stable river reaches. Management actions that increase stream stability are likely to result in expansion of the mussel fauna and restoration of a valuable component of ecosystem function in this region. Published in 2006 by John Wiley & Sons, Ltd. [source] | ||||||||||