Home About us Contact
|
Home About us Contact | ||
|
|
||
Habitat Islands (habitat + island)
Selected AbstractsEffects 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] Habitat islands in fire-prone vegetation: do landscape features influence community composition?JOURNAL OF BIOGEOGRAPHY, Issue 5-6 2002Peter J. Clarke Aim, Location Landscape features, such as rock outcrops and ravines, can act as habitat islands in fire-prone vegetation by influencing the fire regime. In coastal and sub-coastal areas of Australia, rock outcrops and pavements form potential habitat islands in a matrix of fire-prone eucalypt forests. The aim of this study was to compare floristic composition and fire response traits of plants occurring on rocky areas and contrast them with the surrounding matrix. Methods Patterns of plant community composition and fire response were compared between rocky areas and surrounding sclerophyll forests in a range of climate types to test for differences. Classification and ordination were used to compare floristic composition and univariate analyses were used to compare fire response traits. Results The rock outcrops and pavements were dissimilar in species composition from the forest matrix but shared genera and families with the matrix. Outcrops and pavements were dominated by scleromorphic shrubs that were mainly killed by fire and had post-fire seedling recruitment (obligate seeders). In contrast, the most abundant species in the adjacent forest matrix were species that sprout after fire (sprouters). Main conclusions Fire frequency and intensity are likely to be less on outcrops than in the forest matrix because the physical barrier of rock edges disrupts fires. Under the regime of more frequent fires, obligate seeders have been removed or reduced in abundance from the forest matrix. This process may have also operated over evolutionary time-scales and resulted in convergence towards obligate seeding traits on outcrop fire shadows. In contrast, there may have been convergence towards sprouting in the forest matrix as a result of selection for persistence under a regime of frequent fire. [source] Population genetic structure reveals terrestrial affinities for a headwater stream insectFRESHWATER BIOLOGY, Issue 10 2007DEBRA S. FINN Summary 1. The spatial distribution of stream-dwelling organisms is often considered to be limited primarily according to the hierarchical structure of the hydrologic network, and previous conceptual models of population genetic structure have reflected this generality. Headwater specialists, however, are confined to short upstream sections of the network, and therefore are unlikely to respond in the same way as species with a broader range of habitat tolerance. 2. Here, we propose a model to describe spatial patterns of genetic diversity in headwater specialists with a limited ability for among-stream dispersal. The headwater model predicts a partitioning of genetic variance according to higher-elevation ,islands' of terrestrial habitat that provide required headwater stream conditions. The model therefore expects a geographic pattern of genetic variance similar to that expected for low-dispersal terrestrial species occupying the adjacent habitat. 3. Using a 1032-bp mitochondrial DNA fragment encompassing parts of the COI and COII genes, we demonstrate that Madrean Sky Islands populations of the giant water bug Abedus herberti conform to the proposed headwater model. Furthermore, they exhibit phylogeographic patterns broadly concordant with those shown for several terrestrial species in the region, including a major zone of discontinuity in the Chiricahua mountain range. 4. Overall, populations are highly isolated from one another, and a nested clade analysis suggested that A. herberti population structure, similarly to terrestrial Sky Islands species studied previously, has been influenced by Pleistocene climatic cycles causing expansion and contraction of temperate woodland habitat. 5. Because they have no ability to disperse among present-day mountaintop habitat islands, A. herberti and other headwater species with limited dispersal ability are vulnerable to the projected increasing rate of climatic warming in this region. [source] Land use change and the dependence of national priority species on protected areasGLOBAL CHANGE BIOLOGY, Issue 9 2008SARAH F. JACKSON Abstract The establishment and maintenance of a system of protected areas is central to regional and global strategies for the conservation of biodiversity. The current global trend towards human population growth and widespread environmental degradation means that such areas are becoming increasingly isolated, fragmented habitat islands. In regions in which this process is well advanced, a high proportion of species are thus predicted to have become restricted to protected areas. Here, using uniquely detailed datasets for Britain, a region with close to the global level of percentage coverage by statutory protected areas, we determine the extent of restriction of species of conservation concern to these areas. On the basis of currently known distributions, more than a half of such species are highly dependent on protected areas for their continued persistence, occurring either entirely or largely within their bounds. Such coverage is of particular importance for those species with narrower distributions, and therefore, under the greatest threats, underlining the vital importance of adequately resourcing, maintaining, and developing protected areas to prevent these species from being lost. [source] Factors determining mammal species richness on habitat islands and isolates: habitat diversity, disturbance, species interactions and guild assembly rulesGLOBAL ECOLOGY, Issue 1 2000Barry J. Fox Abstract 1For over three decades the equilibrium theory of island biogeography has galvanized studies in ecological biogeography. Studies of oceanic islands and of natural habitat islands share some similarities to continental studies, particularly in developed regions where habitat fragmentation results from many land uses. Increasingly, remnant habitat is in the form of isolates created by the clearing and destruction of natural areas. Future evolution of a theory to predict patterns of species abundance may well come from the application of island biogeography to habitat fragments or isolates. 2In this paper we consider four factors other than area and isolation that influence the number and type of mammal species coexisting in one place: habitat diversity, habitat disturbance, species interactions and guild assembly rules. In all examples our data derive from mainland habitat, fragmented to differing degrees, with different levels of isolation. 3Habitat diversity is seen to be a good predictor of species richness. Increased levels of disturbance produce a relatively greater decrease in species richness on smaller than on larger isolates. Species interactions in the recolonization of highly disturbed sites, such as regenerating mined sites, is analogous to island colonization. Species replacement sequences in secondary successions indicate not just how many, but which species are included. Lastly, the complement of species established on islands, or in insular habitats, may be governed by guild assembly rules. These contributions may assist in taking a renewed theory into the new millennium. [source] Single host trees in a closed forest canopy matrix: a highly fragmented landscape?JOURNAL OF APPLIED ENTOMOLOGY, Issue 9-10 2007J. Müller Abstract:, Whether trees represent habitat islands and therefore are influenced by similar biogeographic processes as ,real' islands is controversial. For trees in highly fragmented landscapes the impacts of spatial isolation on arthropod communities have already been demonstrated. However, we have almost no evidence that in large forests the arthropod communities on single trees in a closed canopy matrix are influenced by similar processes. In the present study the influence of spatial isolation on the specialized oak crown fauna was analysed in a large broadleaved forest area in northern Bavaria, Germany. The dependence of specialists on the proportion of oaks in the surrounding forest was investigated by using flight interception traps (67 on oak, 19 on beech). As target species, saproxylic and herbivorous Coleoptera and Heteroptera were sampled. The following two hypotheses were tested: (1) The proportion of oak specialists differs for oaks in beech forests and oaks in oak forests. (2) The proportion of oak specialists increases with the proportion of oaks in the surrounding forest. For all species groups, the proportion of oak specialists was higher in oak crowns than in beech crowns. Herbivorous beetles and true bugs showed a higher proportion of specialists in oak forests than on single oaks in beech forests. The proportion of herbivorous oak specialists increased significantly with increasing numbers of adjacent oak trees, while saproxylic Coleoptera showed no relationship to oak density. For herbivorous Coleoptera a threshold of higher proportion occurred where >30% oak was present, and for Heteroptera a first threshold was identified at values >70% and a second at >30%. This indicates that larger habitat patches within a closed forest canopy matrix support larger populations of herbivorous oak specialists. Hence, similar effects of spatial isolation might occur in a closed forest as have already been shown for highly fragmented open landscapes. [source] Local,regional boundary shifts in oribatid mite (Acari: Oribatida) communities: species,area relationships in arboreal habitat islands of a coastal temperate rain forest, Vancouver Island, CanadaJOURNAL OF BIOGEOGRAPHY, Issue 9 2007Zoë Lindo Abstract Aim, This study investigates the species,area relationship (SAR) for oribatid mite communities of isolated suspended soil habitats, and compares the shape and slope of the SAR with a nested data set collected over three spatial scales (core, patch and tree level). We investigate whether scale dependence is exhibited in the nested sampling design, use multivariate regression models to elucidate factors affecting richness and abundance patterns, and ask whether the community composition of oribatid mites changes in suspended soil patches of different sizes. Location, Walbran Valley, Vancouver Island, Canada. Methods, A total of 216 core samples were collected from 72 small, medium and large isolated suspended soil habitats in six western redcedar trees in June 2005. The relationship between oribatid species richness and habitat volume was modelled for suspended soil habitat isolates (type 3) and a nested sampling design (type 1) over multiple spatial scales. Nonlinear estimation parameterized linear, power and Weibull function regression models for both SAR designs, and these were assessed for best fit using R2 and Akaike's information criteria (,AIC) values. Factors affecting oribatid mite species richness and standardized abundance (number per g dry weight) were analysed by anova and linear regression models. Results, Sixty-seven species of oribatid mites were identified from 9064 adult specimens. Surface area and moisture content of suspended soils contributed to the variation in species richness, while overall oribatid mite abundance was explained by moisture and depth. A power-law function best described the isolate SAR (S = 3.97 × A0.12, R2 = 0.247, F1,70 = 22.450, P < 0.001), although linear and Weibull functions were also valid models. Oribatid mite species richness in nested samples closely fitted a power-law model (S = 1.96 × A0.39, R2 = 0.854, F1,18 = 2693.6, P < 0.001). The nested SAR constructed over spatial scales of core, patch and tree levels proved to be scale-independent. Main conclusions, Unique microhabitats provided by well developed suspended soil accumulations are a habitat template responsible for the diversity of canopy oribatid mites. Species,area relationships of isolate vs. nested species richness data differed in the rate of accumulation of species with increased area. We suggest that colonization history, stability of suspended soil environments, and structural habitat complexity at local and regional scales are major determinants of arboreal oribatid mite species richness. [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] Habitat islands in fire-prone vegetation: do landscape features influence community composition?JOURNAL OF BIOGEOGRAPHY, Issue 5-6 2002Peter J. Clarke Aim, Location Landscape features, such as rock outcrops and ravines, can act as habitat islands in fire-prone vegetation by influencing the fire regime. In coastal and sub-coastal areas of Australia, rock outcrops and pavements form potential habitat islands in a matrix of fire-prone eucalypt forests. The aim of this study was to compare floristic composition and fire response traits of plants occurring on rocky areas and contrast them with the surrounding matrix. Methods Patterns of plant community composition and fire response were compared between rocky areas and surrounding sclerophyll forests in a range of climate types to test for differences. Classification and ordination were used to compare floristic composition and univariate analyses were used to compare fire response traits. Results The rock outcrops and pavements were dissimilar in species composition from the forest matrix but shared genera and families with the matrix. Outcrops and pavements were dominated by scleromorphic shrubs that were mainly killed by fire and had post-fire seedling recruitment (obligate seeders). In contrast, the most abundant species in the adjacent forest matrix were species that sprout after fire (sprouters). Main conclusions Fire frequency and intensity are likely to be less on outcrops than in the forest matrix because the physical barrier of rock edges disrupts fires. Under the regime of more frequent fires, obligate seeders have been removed or reduced in abundance from the forest matrix. This process may have also operated over evolutionary time-scales and resulted in convergence towards obligate seeding traits on outcrop fire shadows. In contrast, there may have been convergence towards sprouting in the forest matrix as a result of selection for persistence under a regime of frequent fire. [source] Are tree trunks habitats or highways?AUSTRALIAN JOURNAL OF ENTOMOLOGY, Issue 4 2002A comparison of oribatid mite assemblages from hoop-pine bark, litter Abstract Oribatid mites (Acari: Oribatida) are among the most diverse and abundant inhabitants of forest soil and litter, but also have species-rich assemblages on bark and in the canopies of trees. It is unclear whether the trunk of a tree acts simply as a ,highway' for movement of mites into and out of the canopy, or whether the trunk has a distinctive acarofauna. We compare oribatid assemblages from the trunk bark of hoop pine (Araucaria cunninghamii) with those from litter collected beneath the same trees. A 1.0 by 0.5 m area of bark was sampled from three trees at each of five sites using a knockdown insecticide. A 1-L sample of leaf litter was collected as close as possible to the base of each sampled tree. Mites were extracted using Tullgren funnels, identified to genus and morphospecies, and counted. Assemblages were almost 100% distinct, with only one oribatid morphospecies (Pseudotocepheus sp.) collected from both litter and bark. Litter had a higher taxon richness than bark in total and per sample, but oribatids made up a greater percentage of the acarofauna in the bark samples. We had expected that the more consistent physical substrate of bark would be reflected in greater similarity of oribatid faunas on trunks than in litter; however, the opposite proved to be the case. We conclude that hoop-pine trunks are habitats rather than highways for oribatid mites. Based on the observed higher turnover among bark faunas, tree trunks may represent habitat islands whose colonisation by particular oribatid species is more stochastic than that of the more continuous ,sea' of litter. [source] | ||||||||||||||||||||||