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Matrix Quality (matrix + quality)
Selected AbstractsNon-optimal animal movement in human-altered landscapesFUNCTIONAL ECOLOGY, Issue 6 2007LENORE FAHRIG Summary 1I synthesize the understanding of the relationship between landscape structure and animal movement in human-modified landscapes. 2The variety of landscape structures is first classified into four categories: continuous habitat, patchy habitat with high-quality matrix, patchy habitat with low-quality matrix, and patchy, ephemeral habitat. Using this simplification I group the range of evolved movement parameters into four categories or movement types. I then discuss how these movement types interact with current human-caused landscape changes, and how this often results in non-optimal movement. 3From this synthesis I develop a hypothesis that predicts the relative importance of the different population-level consequences of these non-optimal movements, for the four movement types. 4Populations of species that have inhabited landscapes with high habitat cover or patchy landscapes with low-risk matrix should have evolved low boundary responses and moderate to high movement probabilities. These species are predicted to be highly susceptible to increased movement mortality resulting from habitat loss and reduced matrix quality. 5In contrast, populations of species that evolved in patchy landscapes with high-risk matrix or dynamic patchy landscapes are predicted to be highly susceptible to decreased immigration and colonization success, due to the increasing patch isolation that results from habitat loss. 6Finally, I discuss three implications of this synthesis: (i) ,least cost path' analysis should not be used for land management decisions without data on actual movement paths and movement risks in the landscape; (ii) ,dispersal ability' is not simply an attribute of a species, but varies strongly with landscape structure such that the relative rankings of species' dispersal abilities can change following landscape alteration; and (iii) the assumption that more mobile species are more resilient to human-caused landscape change is not generally true, but depends on the structure of the landscape where the species evolved. [source] Short-term transformation of matrix into hospitable habitat facilitates gene flow and mitigates fragmentationJOURNAL OF ANIMAL ECOLOGY, Issue 6 2007NIELS BLAUM Summary 1Habitat fragmentation has major implications for demography and genetic structure of natural plant and animal populations as small and isolated populations are more prone to extinction. Therefore, many recent studies focus on spatial fragmentation. 2However, the temporal configuration of suitable habitat may also influence dispersal and gene flow in fragmented landscapes. We hypothesize that short-term switching of inhospitable matrix areas into suitable habitat can mitigate effects of spatial fragmentation in natural and seminatural ecosystems. 3To test our hypothesis, we investigated the hairy-footed gerbil (Gerbillurus paeba, Smith 1836), a ground-dwelling rodent, in fragmented Kalahari savannah areas. Here, rare events of high above mean annual rainfall suggest short-term matrix suitability. 4During the field survey in ,matrix' areas in the Kalahari (shrub encroachment by heavy grazing) we never observed the hairy-footed gerbil in years of average rainfall, but observed mass occurrences of this species during rare events of exceptionally high rainfall. 5In a second step, we developed an agent-based model simulating subpopulations in two neighbouring habitats and the separating matrix. Our mechanistic model reproduces the mass occurrences as observed in the field and thus suggests the possibly underlying processes. In particular, the temporary improvement in matrix quality allows reproduction in the matrix, thereby causing a substantial increase in population size. 6The model demonstrates further how the environmental trigger (rainfall) impacts genetic connectivity of two separated subpopulations. We identified seasonality as a driver of fragmentation but stochasticity leading to higher connectivity. 7We found that our concept of temporal fragmentation can be applied to numerous other fragmented populations in various ecological systems and provide examples from recent literature. We conclude that temporal aspects of fragmentation must be considered in both ecological research and conservation management. [source] Behavioural responses to habitat patch boundaries restrict dispersal and generate emigration,patch area relationships in fragmented landscapesJOURNAL OF ANIMAL ECOLOGY, Issue 4 2003Nicolas Schtickzelle Summary 1We studied the consequences of behaviour at habitat patch boundaries on dispersal for the bog fritillary butterfly Proclossiana eunomia Esper in two networks of habitat differing in fragmentation and matrix quality. We tested for differences in responses to patch boundaries according to the fragmentation level of the network by analysing movement paths of adult butterflies. 2Butterflies systematically engaged in U-turns when they reached a boundary in the fragmented network while they crossed over boundaries in more than 40% of boundary encounters in the continuous one. 3We applied the Virtual Migration model (Hanski, Alho & Moilanen 2000) to capture,mark,recapture data collected in both networks. The model indicated (i) a lower dispersal rate and (ii) a lower survival during dispersal in the fragmented network. This latter difference is likely to be the key biological process leading to behavioural avoidance of patch boundary crossings. 4On the basis of this behavioural difference, we designed an individual-based simulation model to explore the relationship between patch area, boundary permeability and emigration rate. 5Predictions of the model fitted observed results of the effect of patch area on emigration rate according to fragmentation: butterflies are more likely to leave small patches than large ones in fragmented landscapes (where patch boundary permeability is low), while this relationship disappears in more continuous landscapes (where patch boundary permeability is high). [source] Critical thresholds associated with habitat loss: a review of the concepts, evidence, and applicationsBIOLOGICAL REVIEWS, Issue 1 2010Trisha L. Swift A major conservation concern is whether population size and other ecological variables change linearly with habitat loss, or whether they suddenly decline more rapidly below a "critical threshold" level of habitat. The most commonly discussed explanation for critical threshold responses to habitat loss focus on habitat configuration. As habitat loss progresses, the remaining habitat is increasingly fragmented or the fragments are increasingly isolated, which may compound the effects of habitat loss. In this review we also explore other possible explanations for apparently nonlinear relationships between habitat loss and ecological responses, including Allee effects and time lags, and point out that some ecological variables will inherently respond nonlinearly to habitat loss even in the absence of compounding factors. In the literature, both linear and nonlinear ecological responses to habitat loss are evident among simulation and empirical studies, although the presence and value of critical thresholds is influenced by characteristics of the species (e.g. dispersal, reproduction, area/edge sensitivity) and landscape (e.g. fragmentation, matrix quality, rate of change). With enough empirical support, such trends could be useful for making important predictions about species' responses to habitat loss, to guide future research on the underlying causes of critical thresholds, and to make better informed management decisions. Some have seen critical thresholds as a means of identifying conservation targets for habitat retention. We argue that in many cases this may be misguided, and that the meaning (and utility) of a critical threshold must be interpreted carefully and in relation to the response variable and management goal. Despite recent interest in critical threshold responses to habitat loss, most studies have not used any formal statistical methods to identify their presence or value. Methods that have been used include model comparisons using Akaike information criterion (AIC) or t -tests, and significance testing for changes in slope or for polynomial effects. The judicious use of statistics to help determine the shape of ecological relationships would permit greater objectivity and more comparability among studies. [source] | ||||||||||