Increasing Patch Size Research Articles

Faunal Communities Are Invariant to Fragmentation in Experimental Seagrass Landscapes.

Human-driven habitat fragmentation is cited as one of the most pressing threats facing many coastal ecosystems today. Many experiments have explored the consequences of fragmentation on fauna in one foundational habitat, seagrass beds, but have either surveyed along a gradient of existing patchiness, used artificial materials to mimic a natural bed, or sampled over short timescales. Here, we describe faunal responses to constructed fragmented landscapes varying from 4–400 m2 in two transplant garden experiments incorporating live eelgrass (Zostera marina L.). In experiments replicated within two subestuaries of the Chesapeake Bay, USA across multiple seasons and non-consecutive years, we comprehensively censused mesopredators and epifaunal communities using complementary quantitative methods. We found that community properties, including abundance, species richness, Simpson and functional diversity, and composition were generally unaffected by the number of patches and the size of the landscape, or the intensity of sampling. Additionally, an index of competition based on species co-occurrences revealed no trends with increasing patch size, contrary to theoretical predictions. We extend conclusions concerning the invariance of animal communities to habitat fragmentation from small-scale observational surveys and artificial experiments to experiments conducted with actual living plants and at more realistic scales. Our findings are likely a consequence of the rapid life histories and high mobility of the organisms common to eelgrass beds, and have implications for both conservation and restoration, suggesting that even small patches can rapidly promote abundant and diverse faunal communities.

Mass Extinction and the Disappearance of Unknown Mammal Species: Scenario and Perspectives of a Biodiversity Hotspot's Hotspot.

We aimed to determine the conservation status of medium- and large-sized mammals and evaluate the impact of 500 years of forest fragmentation on this group of animals in the Pernambuco Endemism Center, in the biogeographical zone of the Atlantic forest north of the São Francisco River in northeastern Brazil. Line transect surveys were performed in 21 forest fragments, resulting in a checklist of the mammals of the entire Pernambuco Endemism Center area. We ran a generalized linear model (Factorial ANCOVA) to analyze to what extent the vegetation type, fragment area, isolation, sampling effort (as total kilometers walked), or higher-order interactions predicted (a) richness and (b) sighting rates. To determine if the distribution of the species within the forest fragments exhibited a nested pattern, we used the NODF metric. Subsequently, we performed a Binomial Logistic Regression to predict the probability of encountering each species according to fragment size. Out of 38 medium- and large-sized mammal species formerly occurring in the study area, only 53.8% (n = 21) were sighted. No fragment hosted the entire remaining mammal community, and only four species (19%) occurred in very small fragments (73.3% of the remaining forest fragments, with a mean size of 2.8 ha). The mammalian community was highly simplified, with all large mammals being regionally extinct. Neither the species richness nor sighting rate was controlled by the vegetation type, the area of the forest fragments, isolation or any higher-order interaction. Although a highly significant nested subset pattern was detected, it was not related to the ranking of the area of forest fragments or isolation. The probability of the occurrence of a mammal species in a given forest patch varied unpredictably, and the probability of detecting larger species was even observed to decrease with increasing patch size. In an ongoing process of mass extinction, half of the studied mammals have gone extinct. The remaining medium-sized mammal community is highly simplified and homogenized. The persistence of these species in a forest patch is determined by their ability to adapt to a novel simplified diet, the efficient use of the surrounding matrix without being engulfed by the sink effect, and escaping hunting. Our results suggest that the 21st century medium-sized mammalian fauna of this region will comprise only four species unless strict conservation measures are implemented immediately and every forest fragment is effectively protected.

Spatial metrics effect of forest fragmentation on forest bird abundance and site occupancy probability: the influence of patch size and isolation

The persistence of species taxa within fragmented habitats is dependent on the source–sink metapopulation processes, and forest patch size and isolation are key factors. Unveiling species–patch area and/or species–patch isolation relationships may help provide crucial information for species and landscape management. In this study, relationship between forest patch size and isolation with abundance and occupancy probability of forest-dependent birds was investigated. This study was based within a coastal landscape that faces deleterious human activities such as clearing for agriculture. The study aimed to answer the question of whether the size and extent of isolation of forest patches influence abundance and/or occupancy probability of forest-specialist and generalist birds. Two bird species, namely Tiny Greenbul Phyllastrephus debilis subsp. rabai and Yellow-bellied Greenbul Chlorocichla flaviventris, were used as models. Birds were surveyed using distance sampling methods, and spatial metrics were measured from satellite imagery. Focal forest size and distance between forest patches were the most influential metrics whereby abundance and occupancy probabilities increased with increasing patch size, but were negatively influenced by increasing gaps between patches. These findings provide evidence of the existence of patch size/ isolation–occupancy relationships characterised by higher occupancy rate of large patches and distance-dependent dispersal, which decreased with increasing gaps between patches. Controlling deleterious human activities that reduce forest size should be a priority for the long-term conservation of forest-dependent birds.

Velocity‐saturation relation in partially saturated rocks: Modelling the effect of injection rate changes

ABSTRACTThe relationship between P‐wave velocity and fluid saturation in a porous medium is of importance for reservoir rock characterization. Forced imbibition experiments in the laboratory reveal rather complicated velocity–saturation relations, including rollover‐like patterns induced by injection rate changes. Poroelasticity theory‐based patchy saturation models using a constant fluid patch size are not able to describe these velocity–saturation relations. Therefore, we incorporate a saturation‐dependent patch size function into two models for patchy saturation. This recipe allows us to model observed velocity–saturation relations obtained for different and variable injection rates. The results reveal an increase in patch size with fluid saturation and show a reduction in the patch size for decreasing injection rate. This indicates that there can exist a distinct relation between patch size and injection rate. We assess the relative importance of capillarity on velocity–saturation relations and find that capillarity stiffening impairs the impact of patch size changes. Capillarity stiffening appears to be a plausible explanation when a decrease in the injection rate is expected to boost the importance of capillarity.

Size-related change in Nitraria sphaerocarpa patches shifts the shrub-annual interaction in an arid desert, northwestern China

In arid and semi-arid ecosystems, the effect of shrubs on their understory plants has been frequently reported. Many previous studies have shown that both facilitation and competition act simultaneously, and their balance changes in response to spatial or temporal variations in environmental stresses. Yet, we know little about how the interaction varies between shrubs and their understory plants in vegetation patches with different characteristics. Here, an empirical investigation was conducted in Hexi desert region of northwest China, to evaluate how the net effect of Nitraria sphaerocarpa shrubs on the herbaceous species varies across different sizes of N. sphaerocarpa patches. Our study showed that herbaceous species perform better on small shrub patches. But the magnitude of this facilitative effect decreased with increasing patch size, and finally shifted to interference in large patches. The results indicated that these negative shifts in plant interactions were not clearly related to ‘shrub-island effect’ in terms of nutrient accumulation or soil properties improvement, but may be explained by the variation in other abiotic factors, such as soil moisture and available light. Changes in root distribution and canopy structure of N. sphaerocarpa shrubs with the increase of patch size seem to also partly explain the variation in shrub-understory species interactions, as a result of increased above- and below-ground niche overlaps.

Dispersal mode mediates the effect of patch size and patch connectivity on metacommunity diversity

Summary Metacommunity theory predicts that increasing patch size and patch connectivity can alter local species diversity by affecting either colonization rates, extinction rates or both. Although species’ dispersal abilities or ‘dispersal mode’ (e.g. gravity‐, wind‐ or animal‐dispersed seeds) can mediate the effects of patch size and connectivity on diversity, these important factors are frequently overlooked in empirical metacommunity work. We use a natural metacommunity of aspen stands within a grassland matrix to determine whether dispersal mode alters the influence of stand size and connectivity on understorey plant diversity. We sampled the same area in each patch, controlled for the presence of matrix species in aspen stands, and tested for the effects of size, connectivity and dispersal mode on metacommunity richness. Because dispersal groups responded differently to patch size and connectivity, we created a null model and assessed ungulate activity to explore whether competitive dynamics or herbivory were driving diversity patterns. Animal‐dispersed species and species with no dispersal aid had higher diversity per unit area in larger stands, likely because large stands can both support larger populations that are less prone to extinction and may also attract seed‐dispersing animals such as birds and small mammals that are sensitive to edge effects. Consistent with other empirical work, we found a positive relationship between diversity and connectivity for wind‐dispersed species. However, we detected a negative effect of stand connectivity on the diversity of species with no dispersal aid, possibly due to the presence of other highly competitive species groups dominating well‐connected patches, as our null model results suggest. We found no evidence for higher ungulate activity in highly connected patches, suggesting that herbivory may not be driving the decline in diversity of plants with no dispersal aid. Synthesis. Overall, we see a positive effect of stand area on diversity for most groups despite sampling equal area in all stands, which is a prediction of metacommunity theory that is normally overlooked. Our results demonstrate the importance of considering variation in the dispersal modes of focal species for explaining the diversity patterns of natural metacommunities.

Effects of habitat structure, human disturbance, and habitat connectivity on urban forest bird communities

As urbanization accelerates, urban biodiversity conservation is becoming a great concern for the maintenance of urban ecosystem functions. In particular, forest bird communities in urban areas have been recognized as a conservation target because of their functions in food webs and ecosystem services. But our understanding of which local- and landscape-scale factors influence native bird communities within urban green spaces is still insufficient to provide managers with information for effectively planning biodiversity management programs. Here we examine how local habitat characteristics, human disturbance, and habitat connectivity influence the diversity of forest bird communities in 44 small forest patches (0.5–20.0 ha) embedded in an urbanized landscape. Patch size exerted a positive influence on the diversity of most bird functional groups, and it had the greatest effects on total abundance and species richness. The second most important factor was human disturbance. Remnant patches with lower levels of human disturbance had higher diversity than newly established patches where intense human activities occurred more frequently. In addition, vegetation complexity and habitat connectivity were positively related to total species richness and abundance, respectively, but they were less important. Management strategies for the conservation of urban forest birds, therefore, should consider not only local improvements in habitat structure – through increased patch size, reduced human disturbance, and increased vegetation complexity – but also the maintenance of habitat connectivity.

High lifetime inbreeding depression counteracts the reproductive assurance benefit of selfing in a mass-flowering shrub.

BackgroundDecreases in mate and/or pollinator availability would be expected to affect the selective pressure on plant mating systems. An increase in self-fertilization may evolve to compensate for the negative effects of pollination failure. However, the benefit of selfing in variable pollination environments depends on the relative fitnesses of selfed and outcrossed progeny. We investigated the potential for selfing to provide reproductive assurance over the lifetime of a long-lived perennial species and its variation between plant patches of various sizes. Patch size is likely to affect mate and pollinator availabilities, thereby affecting pollination success and the rate of selfing. We estimated fruit and seed set, reproductive assurance, self-compatibility, the multilocus patch selfing rate and lifetime inbreeding depression in natural patches of Rhododendron ferrugineum (Ericaceae), a mass-flowering species characterized by considerable patch size variation (as estimated by the total number of inflorescences).ResultsOpen seed set declined linearly with increasing patch size, whereas pollinator-mediated seed set (emasculated flowers) was not significantly affected. Progeny array analysis indicated that the selfing rate declined with increasing patch size, consistent with greater reproductive assurance in small sparse patches than in large, dense patches. However, fruit set and adult fitness decreased with decreasing patch size, with an estimated mean lifetime inbreeding depression of 0.9 (obtained by comparing F values in adults and progenies).ConclusionsLifetime inbreeding depression strongly counteracts the advantage of reproductive assurance due to selfing in this long-lived species. The poor fitness of selfed offspring should counteract any evolution towards selfing, despite its potential to alleviate the negative consequences of pollen limitation. This study highlights the need to estimate lifetime inbreeding depression, together with mating system and pollination parameters, if we are to understand the actual benefit of selfing and avoid the overestimation of reproductive assurance.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-014-0243-7) contains supplementary material, which is available to authorized users.

Oscillations of Min-proteins in micropatterned environments: a three-dimensional particle-based stochastic simulation approach

The Min-proteins from E. coli and other bacteria are the best characterized pattern forming system in cells and their spatiotemporal oscillations have been successfully reconstituted in vitro. Different mathematical and computational models have been used to better understand these oscillations. Here we use particle-based stochastic simulations to study Min-oscillations in patterned environments. We simulate a rectangular box of length 10 μm and width 5 μm that is filled with grid or checkerboard patterns of different patch sizes and distances. For this geometry, we find different stable oscillation patterns, typically pole-to-pole oscillations along the minor axis and striped oscillations along the major axis. The Min-oscillations can switch from one pattern to the other, either effected by changes in pattern geometry or stochastically. By automatic analysis of large-scale computer simulations, we show quantitatively how the perturbing effect of increased patch distance can be rescued by increased patch size. We also show that striped oscillations occur robustly in arbitrarily shaped filamentous E. coli cells. Our results highlight the robustness and variability of Min-oscillations, put limits on the effect of putative division sites, and provide a powerful computational framework for future studies of protein self-organization in patterned environments.

Do habitat fragmentation and fire influence variation of plant species composition, structure and diversity within three regional ecosystems on the Sunshine Coast, Queensland, Australia?

Habitat fragmentation is considered to be one of the greatest threats to biodiversity. Species richness is predicted to decrease with decreasing patch size and increasing isolation, and this has been shown in some ecosystems. However, few studies have specifically investigated the effects of fragmentation on specific vegetation types, or compared different vegetation types within the same region. In this study, we assessed the influence of habitat fragmentation and time since fire on the floristic composition, structure and diversity of three ecosystems with varying fire proneness within the Sunshine Coast region. This study found that the tall-open forest ecosystem (RE 12.9-10.14) had higher overall species richness within fixed sample areas used for this study than did either open forest (RE 12.5.3) or gallery rainforest (RE 12.3.1), because it was composed of species typical of each of these ecosystem types. Open forest species richness was found mostly in the lower stratum, whereas gallery rainforest diversity was found in the upper stratum. Species richness decreased with increasing isolation in the open forest ecosystem where seeds are mostly abiotically dispersed. However, this study did not find strong evidence for reduced species richness within smaller patches in any ecosystem type studied; instead, finding species richness decreased with increasing patch size in the open forest ecosystem. Overall, across ecosystems, time since fire affected vegetation structure, but in fire-prone ecosystems, time since fire was not a determinant of species richness within the sites studied.

Beneficial insects in urban environments: Parasitism rates increase in large and less isolated plant patches via enhanced parasitoid species richness

In urban habitats, plant resources for herbivorous insects and their parasitoids are spatially subdivided and embedded in a matrix of built environment. These conditions could affect insect colonization and persistence, leading to altered trophic interactions. Here we tested whether spatial attributes (size and isolation) of patches of an urban spontaneous plant (Commelina erecta) affect the parasitism rates on a specialist leaf miner (Liriomyza commelinae) from its diverse parasitoid assemblage. To achieve this goal we performed an observational study in Córdoba city (Argentina), by sampling 893 naturally established C. erecta patches on 18 neighborhoods. Overall parasitism rates of the leaf miner augmented at increasing patch size and decreasing patch isolation, and those effects were mediated by changes in parasitoid richness. Leaf miners in larger or less isolated plant patches supported more parasitoid species which, independently of host abundance, led to higher parasitism rates. Individual parasitoid species showed different responses to patch attributes, with some species being more efficient in large or less isolated plant patches whereas parasitism rates of other species were independent of patch attributes. Our results highlight the importance of spatial availability of urban plant resources for parasitoid diversity and for the key process of biological control in which they are involved. Understanding how natural enemies respond to the patchiness of herbivore resources in the urban context could contribute to the development of strategies to preserve beneficial insects in these highly modified landscapes.

How should parents adjust the size of their young in response to local environmental cues?

Models of parental investment typically assume that populations are well mixed and homogeneous and have devoted little attention to the impact of spatial variation in the local environment. Here, in a patch-structured model with limited dispersal, we assess to what extent resource-rich and resource-poor mothers should alter the size of their young in response to the local environment in their patch. We show that limited dispersal leads to a correlation between maternal and offspring environments, which favours plastic adjustment of offspring size in response to local survival risk. Strikingly, however, resource-poor mothers are predicted to respond more strongly to local survival risk, whereas resource-rich mothers are predicted to respond less strongly. This lack of sensitivity on the part of resource-rich mothers is favoured because they accrue much of their fitness through dispersing young. By contrast, resource-poor mothers accrue a larger fraction of their fitness through philopatric young and should therefore respond more strongly to local risk. Mothers with more resources gain a larger share of their fitness through dispersing young partly because their fitness in the local patch is constrained by the limited number of local breeding spots. In addition, when resource variation occurs at the patch level, the philopatric offspring of resource-rich mothers face stronger competition from the offspring of other local mothers, who also enjoy abundant resources. The effect of limited local breeding opportunities becomes less pronounced as patch size increases, but the impact of patch-level variation in resources holds up even with many breeders per patch.

Nucleation-driven regeneration promotes post-fire recovery in a Chilean temperate forest

Nucleation is a successional process in which extant vegetation facilitates seed dispersal and recruitment of other individuals and species around focal points in the landscape, leading to ecosystem recovery. This is an important process in disturbed sites where regeneration is limited by abiotic conditions or restrictive seed dispersal. We investigated forest recovery in a large burned area of evergreen temperate rainforest in southern Chile subjected to seasonal soil waterlogging, and assessed the relevance of nucleation processes in overcoming biotic and physical barriers for tree species regeneration. We measured richness and abundance of woody species in relation to patch size, as well as abiotic factors such as light and soil moisture within and outside patches. We found higher tree regeneration in existing patches than in open areas. We recorded an increase of patch size over time, associated with the increase in number of individuals and tree species. Soils in open areas were waterlogged, especially in winter, while patches were not. Trees in patches also acted as perches, enhancing bird-mediated seed rain. Seeds of fleshy-fruited tree species arrived first at patches and seedlings were more frequent in smaller, younger patches, while the number of seedlings of trees with wind-dispersed seeds increased in larger, older patches. Our study shows that woody species seem incapable of recruiting in open and waterlogged soils and depend strongly on extant vegetation patches to establish. In this fire-disturbed evergreen temperate forest regeneration occurs via nucleation, where new individuals contribute to a centrifugal kind of patch growth.

The effect of vertical and horizontal dilution on fertilized patch experiments

A great deal of attention, both negative and positive, has been directed at the potential of large‐scale iron fertilization schemes to sequester carbon by inducing phytoplankton blooms that would, in theory, result in significant export of organic carbon to the deep ocean in high nitrogen ‐ low chlorophyll regions. A suite of iron manipulation or ‘patch’ experiments has been performed over length‐scales of 10s of km. Here, we use a physical‐ecological‐chemical model, with prognostic nitrogen, silica and iron dynamics, to study one of the most successful of these experiments, the Subarctic Ecosystem Response to Iron Enrichment Study (SERIES), focusing on the vertical export of organic material, which is difficult to observe in the field. The implications of large‐scale fertilization, i.e. increasing patch size, are investigated. Our results agree with the general conclusions obtained from the field experiments. Only a modest export of organic carbon occurs (less than 25% of carbon uptake by phytoplankton) at the base of the mixed layer. Furthermore, we show that lateral and vertical supply of silicic acid is necessary to fuel a sustained phytoplankton bloom. Increasing patch size results in less lateral nutrient supply relative to patch area and so a decrease, not only in total production (per unit area), but in the contribution by large phytoplankton due to silica limitation. Most importantly, the export of organic carbon (per unit area) decreases substantially, by nearly an order of magnitude, as scales of 1000 km are approached.

Host location success of root-feeding nematodes in patches that differ in size and quality: A belowground release-recapture experiment

Resource patch size and patch nutritional quality are both important factors influencing local densities of herbivores. The responses of herbivores to resource patch size have been mostly studied in aboveground plant–insect interactions, whereas belowground organisms have received little attention. We studied responses of different root-feeding nematode species associated with marram grass (Ammophila arenaria (L.) Link) to resource patch size and quality. Different nematode species were released in experimental mesocosms filled with dune sand in which we established marram grass patches of varying sizes. Half of the patches of small, medium and large size were fertilized to test if immigration probabilities of nematodes depended on patch quality. We tested the hypotheses that (1) nematodes should aggregate on larger patches and (2) colonization of patches would also depend on patch nutritional quality, with higher nematode recapture rates expected in fertilized patches. Two species (Helicotylenchus pseudorobustus, Hemicycliophora thornei) of the five released species were recaptured in the experiment. The fraction of nematodes immigrating into the rhizosphere of a plant patch increased with patch size (i.e. root biomass), which was in line with predictions of the Resource Concentration Hypothesis. When fractions were recalculated to represent recapture rates per liter of soil, recapture rates of nematodes did not differ among patch sizes, indicating that the increase in recapture rates was directly proportional to the increase in patch size. This suggests that the process through which nematodes located patches was not distinguishable from a random process where entering patches is based on random encounters with patch boundaries. In contrast to our expectation, fertilization had a strong negative effect on patch responses of both nematode species. Our study represents an approach that may be used to explore whether belowground biota behave in similar ways as aboveground biota, in order to determine how perceived differences in environments affect ecological interactions.

Development of Caenorhabditis elegans dauer larvae in growing populations

For species that rely on ephemeral resources, genotype fitness will depend on traits that affect both population growth rates and dispersal. Understanding how such traits are related is central to understanding how they may evolve. Natural populations of Caenorhabditis elegans exhibit rapid population growth within resource-rich patches of decaying organic material and subsequent dispersal, primarily as developmentally-arrested dauer larvae, between patches. The properties of growing populations of C. elegans are, however, poorly understood. Here we show that food availability, dauer pheromone (a measure of conspecific population density) and temperature affect dauer larvae development in growing populations as would be predicted from analyses of single cohorts of worms. We also show that as food patch size increases, dauer larvae are formed prior to patch exhaustion and that the number of dauer larvae present increases after the patch is exhausted, i.e., worms that had not completed development as dauer larvae when the food was exhausted continue development in the absence of bacterial food. Crucially, the subsequent reproductive fitness of dauer larvae that complete development after the exhaustion of the bacterial food patch is reduced in comparison with dauer larvae that develop prior to patch exhaustion. These results demonstrate that population level analyses of C. elegans are feasible, support previous studies of the environmental factors affecting dauer larvae development and suggest an adaptive benefit for variation between isolates in the sensitivity of dauer larvae development.

An Ecoregional Context for Forest Management on National Wildlife Refuges of the Upper Midwest, USA

To facilitate forest planning and management on National Wildlife Refuges, we synthesized multiple data sources to describe land ownership patterns, land cover, landscape pattern, and changes in forest composition for four ecoregions and their associated refuges of the Upper Midwest. We related observed patterns to ecological processes important for forest conservation and restoration, with specific attention to refuge patterns of importance for forest landbirds of conservation priority. The large amount of public land within the ecoregions (31-80%) suggests that opportunities exist for coarse and meso-scale approaches to conserving and restoring ecological processes affecting the refuges, particularly historical fire regimes. Forests dominate both ecoregions and refuges, but refuge forest patches are generally larger and more aggregated than in associated ecoregions. Broadleaf taxa have increased in dominance in the ecoregions and displaced fire-dependent taxa such as pine (Pinus spp.) and other coniferous species; these changes in forest composition have likely also affected refuge forests. Despite compositional changes, larger forest patches on refuges suggests that they may provide better habitat for area-sensitive forest landbirds of mature, compositionally diverse forests than surrounding lands if management continues to promote increased patch size. We reason that although fine-scale research and monitoring for species of conservation priority is important, broad scale (ecoregional) assessments provide crucial context for effective forest and wildlife management in protected areas.

Management-mediated facilitation: Miscanthus sinensis functions as a nurse plant in Satoyama grassland

Facilitation can occur when one species changes form to function as a nurse plant. Miscanthus sinensis grasslands are one component of the typical Satoyama landscape. Due to dieback, the shoot density of M. sinensis decreases with increasing patch size, forming “fairy rings” and subsequently facilitating the establishment of co-existing plants by improving soil and light conditions. M. sinensis forms fairy rings also with human management efforts, particularly burning or cutting. In this study, it was hypothesized that M. sinensis fairy rings created by human management function as a nursery for other species in Sengokuhara grasslands maintained by burning or cutting. To test this hypothesis, the plant species richness inside and outside M. sinensis fairy-ring patches was compared after management events. Species richness was higher inside M. sinensis patches than outside the patches. The type of management method also affected plant species richness. Total number of species and the number of woody plant species were significantly lower in the burned areas than in the cut areas, whereas the reverse was observed for the number of spring ephemeral species. These differences may have been caused by micro-environmental differences generated by management methods and by plant life forms. The results indicate that management-induced facilitation may play an important role in conserving plant species diversity in Satoyama grasslands.

Hot spots of wetland vegetation reduction in relation to human accessibility: differentiating human impacts on natural ecosystems at multiple scales

Human activities have profoundly influenced natural ecosystems, especially wetlands. This study attempted to differentiate the impact of human activities on reductions in wetland vegetation in the Lixiahe wetlands, China, at multiple spatial scales. The reduction in wetland vegetation from 1988 to 2006 was quantified using Landsat data, and moving window analysis was used to detect hot spots of vegetation reduction in the wetlands at window sizes of 150, 1,000 and 2,500 m. Logistic regression was used to examine the influence on occurrence of the hot spots of landscape variables representing accessibility to human settlements and roads. Over the study period, wetland vegetation declined by 69%, which was largely attributable to aquaculture development. The hot spots of wetland vegetation reduction exhibited increasing patch size, but decreasing patch number with increasing window size. The occurrence probability of the hot spots rose significantly with increasing proximity to rural settlements and secondary roads, with only a minor response to the presence of towns. With increasing window size, however, the density of secondary roads and rural settlements were less influential, whereas the presence of major roads had more influence on hot spot occurrence. These trends are reasonable in that wetland use activities in the study area are directly associated with the settlements and roads in the rural areas at local scales, but are also indirectly associated with the major transportation network from a regional perspective. Overall, these results suggested that different human activities, as distinguished by their sources on the landscape, could have different environmental consequences at different scales for scale-dependent features.

EVOLUTIONARY RESPONSES OF DISPERSAL DISTANCE TO LANDSCAPE STRUCTURE AND HABITAT LOSS

It is generally well understood that some ecological factors select for increased and others for decreased dispersal. However, it has remained difficult to assess how the evolutionary dynamics are influenced by the spatio-temporal structure of the environment. We address this question with an individual-based model that enables habitat structure to be controlled through variables such as patch size, patch turnover rate, and patch quality. Increasing patch size at the expense of patch density can select for more or less dispersal, depending on the initial configuration. In landscapes consisting of high-quality and long-lived habitat patches, patch degradation selects for increased dispersal, yet patch loss may select for reduced dispersal. These trends do not depend on the component of life-history that is affected by habitat quality or the component of life-history through which density-dependence operates. Our results are based on a mathematical method that enables derivation of both the evolutionary stable strategy and the stationary genotype distribution that evolves in a polymorphic population. The two approaches generally lead to similar predictions. However, the evolutionary stable strategy assumes that the ecological and evolutionary time scales can be separated, and we find that violation of this assumption can critically alter the evolutionary outcome.