Migration rates of grassland plants along corridors in fragmented landscapes assessed with a cellular automation model

This study investigated the efficacy of linear landscape elements in fragmented landscapes as corridors for perennial grassland species with short-range seed dispersal. Corridors are assumed to be essential for the persistence of metapopulations in fragmented landscapes, but it is unclear to what extent linear landscape elements such as ditch banks and road verges can function as corridors for those species. The principal factors that determine the rate of migration through corridors include the width and habitat quality of patches within a corridor (expressed as the population growth rate λ) and the dispersal capacity of plants (expressed as the slope α of the relationship between seed number and log-distance). A cellular automation model was used to simulate the effects of the principal factors on the rate of migration. Simulations with different levels of the principal factors showed highly significant and positive main effects of dispersal capacity, habitat quality and width of corridors on the migration rate. Significant interactions existed between dispersal capacity × width and dispersal capacity × habitat quality (p<0.0001), indicating that the effects of width and habitat quality depended on the dispersal capacity. In narrow corridors most of the dispersed seeds were deposited outside the corridor, which significantly reduced migration rates, especially for species with long-range dispersal (α=−0.4). In wide corridors (up to 20 m), seed losses were much smaller and migration rates approximated those of continuous habitats. The contribution of the few long-range seeds to the rate of migration was significant when habitat quality was high (population growth rates up to 2.5). However, in all simulations migration rates were very low,i.e.<5 m/yr. It is concluded that linear landscape elements are not effective corridors in fragmented landscapes for plants with short-range seed dispersal, because migration rates are low (<5 m/yr), landscape elements vary in the percentage of high quality patches, and refugia and suitable habitat patches are frequently several kilometres apart, making a cohesive infrastructure of corridors for plants elusive. It is argued that the best way to conserve endangered plant species that encounter dispersal barriers is to harvest seeds from nearby source populations and introduce them as suitable habitats.     

Interactions between plant life span, seed dispersal capacity and fecundity determine metapopulation viability in a dynamic landscape

Classical metapopulation models do not account for temporal changes in the suitability of habitat patches. In reality, however, the carrying capacity of most habitat types is not constant in time due to natural succession processes. In this study, we modeled plant metapopulation persistence in a successional landscape with disappearing and emerging habitat patches, based on a realistic dune slack landscape at the Belgian–French coast. We focused on the effects of the variation of different plant traits on metapopulation persistence in this changing landscape. Therefore, we used a stage based stochastic metapopulation model implemented in RAMAS/Metapop, simulating a large variation in plant traits but keeping landscape characteristics such as patch turnover rate and patch lifespan constant. The results confirm the conclusions of earlier modeling work that seed dispersal distance and seed emigration rate both have an important effect on metapopulation persistence. We also found that high population growth rate or high recruitment considerably decreased the extinction risk of the metapopulation. Additionally, a long plant life span had a strong positive effect on metapopulation persistence, irrespective of the plant's dispersal capacity and population growth rate. Plant species that invest in life span require less investment in offspring and dispersal capacity to avoid extinction, even in dynamic landscapes with deterministic changes in habitat quality. Moreover, metapopulations of long-lived plant species were found to be much less sensitive to high levels of environmental stochasticity than short-lived species.     

Spatial dynamics of the knob-tailed gecko Nephrurus stellatus in a fragmented agricultural landscape

In fragmented landscapes, a species?? dispersal ability and response to habitat condition are key determinants of persistence. To understand the relative importance of dispersal and condition for survival of Nephrurus stellatus (Gekkonidae) in southern Australia, we surveyed 92 woodland remnants three times. This gecko favours early post-fire succession conditions so may be at risk of extinction in the long-unburnt agricultural landscape. Using N-mixture models, we compared the influence of four measures of isolation, patch area and two habitat variables on the abundance and occurrence of N. stellatus, while taking into account detection probability. Patch occupancy was high, despite the long-term absence of fire from most remnants. Distance to the nearest occupied site was the most informative measure of patch isolation, exhibiting a negative relationship with occupancy. Distance to a nearby conservation park had little influence, suggesting that mainland?Cisland metapopulation dynamics are not important. Abundance and occurrence were positively related to ?%-cover of spinifex (Triodia), indicating that niche-related factors may also contribute to spatial dynamics. Patterns of patch occupancy imply that N. stellatus has a sequence of spatial dynamics across an isolation gradient, with patchy populations and source-sink dynamics when patches are within 300?m, metapopulations at intermediate isolation, and declining populations when patches are separated by >1?C2?km. Considering the conservation needs of the community, habitat condition and connectivity may need to be improved before fire can be reintroduced to the landscape. We speculate that fire may interact with habitat degradation and isolation, increasing the risk of local extinctions.     

Determinants of actual functional connectivity for calcareous grassland communities linked by rotational sheep grazing

In fragmented landscapes, plant species persistence depends on functional connectivity in terms of pollen flow to maintain genetic diversity within populations, and seed dispersal to re-colonize habitat patches following local extinction. Connectivity in plants is commonly modeled as a function of the physical distance between patches, without testing alternative dispersal vectors. In addition, pre- and post-dispersal processes such as seed production and establishment are likely to affect patch colonization rates. Here, we test alternative models of potential functional connectivity with different assumptions on source patch effects (patch area and species occupancy) and dispersal (relating to distance among patches, matrix composition, and sheep grazing routes) against empirical patch colonization rates at the community level (actual functional connectivity), accounting for post-dispersal effects in terms of structural elements providing regeneration niches for establishment. Our analyses are based on two surveys in 1989 and in 2009 of 48 habitat specialist plants in 62 previously abandoned calcareous grassland patches in the Southern Franconian Alb in Bavaria, Germany. The best connectivity model S _i , as identified by multi-model inference, combined distance along sheep grazing routes including consistently and intermittently grazed patches with mean species occupancy in 1989 as a proxy for pre-dispersal effects. Community-level patch colonization rates depended to equal degrees on connectivity and post-dispersal process. Our study highlights that actual functional connectivity of calcareous grassland communities cannot be approximated by structural connectivity based on physical distance alone, and modeling of functional connectivity needs to consider pre- and post-dispersal processes.     

The effects of the number,size and isolation of patches along a gradient of native vegetation cover: how can we increment habitat availability?

Habitat availability—or how much habitat species can reach at the landscape scale—depends primarily on the percentage of native cover. However, attributes of landscape configuration such as the number, size and isolation of habitat patches may have complementary effects on habitat availability, with implications for the management of landscapes. Here, we determined whether, and at which percentages of native cover, the number, size and isolation of patches contribute for habitat availability. We quantified habitat availability in 325 landscapes spread across the state of Rio de Janeiro, in the Atlantic Forest hotspot, with either high (>50 %), intermediate (50–30 %), low (30–10 %) or very low (<10 %) percentage of native cover, and for six hypothetical species differing in inter-patch dispersal ability. Above 50 % of native cover, the percentage of cover per se was the only determinant of habitat availability, but below 50 % the attributes of landscape configuration also contributed for habitat availability. The number of patches had a negative effect on habitat availability in landscapes with 50–10 % of native cover, whereas patch size had a positive effect in landscapes with <10 % of native cover. The different species generally responded to the same set of landscape attributes, although to different extents, potentially facilitating decision making for conservation. In landscapes with >50 % of native cover, conservation actions are probably sufficient to guarantee habitat availability, whereas in the remaining landscapes additional restoration efforts are needed, especially to reconnect and/or enlarge remaining habitat patches.     

Spatio-temporal variation in the demographic attributes of a generalist mesopredator

Human land-use practices have dramatically altered the composition and configuration of native habitats throughout many ecosystems. Within heterogeneous landscapes generalist predators often thrive, causing cascading effects on local biological communities, yet there are few data to suggest how attributes of fragmentation influence local population dynamics of these species. We monitored 25 raccoon (Procyon lotor) populations from 2004 to 2009 in a fragmented agricultural landscape to evaluate the influence of local and landscape habitat attributes on spatial and temporal variation in demography. Our results indicate that agricultural ecosystems support increased densities of raccoons relative to many other rural landscapes, but that spatial and temporal variation in demography exists that is driven by non-agricultural habitat attributes rather than the availability of crops. At the landscape scale, both density and population stability were positively associated with the size and contiguity of forest patches, while at the local scale density was positively correlated with plant diversity and the density of tree cavities. In addition, populations occupying forest patches with greater levels of plant diversity and stable water resources exhibited less temporal variability than populations with limited plant species complexity or water availability. The proportion of populations comprised of females was most strongly influenced by the availability of tree cavities and soft mast. Despite the abundance of mesopredators in heterogeneous landscapes, our results indicate that all patches do not contribute equally to the regional abundance and persistence of these species. Thus, a clear understanding of how landscape attributes contribute to variation in demography is critical to the optimization of management strategies.     

Movement across woodland edges suggests plantations and farmland are barriers to dispersal

Landscape Ecology - The behavioural response of animals to edges between habitat patches and the matrix can influence population dynamics and species persistence in fragmented landscapes. We aimed...     

Landscape and habitat filters jointly drive richness and abundance of specialist plants in terrestrial habitat islands

Context

Landscape and habitat filters are major drivers of biodiversity of small habitat islands by influencing dispersal and extinction events in plant metapopulations.

Objectives

We assessed the effects of landscape and habitat filters on the species richness, abundance and trait composition of grassland specialist and generalist plants in small habitat islands. We studied traits related to functional spatial connectivity (dispersal ability by wind and animals) and temporal connectivity (clonality and seed bank persistence) using model selection.

Methods

We sampled herbaceous plants, landscape (local and regional isolation) and habitat filters (inclination, woody encroachment and disturbance) in 82 grassland islands in Hungary.

Results

Isolation decreased the abundance of good disperser specialist plants due to the lack of directional vectors transferring seeds between suitable habitat patches. Clonality was an effective strategy, but persistent seed bank did not support the survival of specialist plants in isolated habitats. Generalist plants were unaffected by landscape filters due to their wide habitat breadth and high propagule availability. Clonal specialist plants could cope with increasing woody encroachment due to their high resistance against environmental changes; however, they could not cope with intensive disturbance. Steep slopes providing environmental heterogeneity had an overall positive effect on species richness.

Conclusions

Specialist plants were influenced by the interplay of landscape filters influencing their abundance and habitat filters affecting species richness. Landscape filtering by isolation influenced the abundance of specialist plants by regulating seed dispersal. Habitat filters sorted species that could establish and persist at a site by influencing microsite availability and quality.

     

Dispersal traits determine plant response to habitat connectivity in an urban landscape

Identification of trait syndromes that make species vulnerable to habitat fragmentation is essential in predicting biodiversity change. Plants are considered particularly vulnerable if their capacities for persistence in and for dispersal among local habitats are low. Here we investigated the influence of easily measured functional traits on the presence of 45 plant species in an urban landscape in north-west Germany where patches were separated by distances consistent with regular plant dispersal range. To describe the spatial configuration of patches we calculated species-specific patch connectivities. Then we assessed plant connectivity responses in distribution models calculated from connectivities and environmental predictors. Twenty (45%) of the analysed species showed a positive connectivity response after accounting for species-specific habitat requirements. These species differed from non-responsive species by functional traits associated with dispersal, including reduced seed numbers and higher terminal velocities relative to non-responsive species. Persistence traits played however no role which we attribute to the environmental conditions of urban habitats and their spatiotemporal characteristics. Our study underlines that even ruderal plants experience dispersal limitation and demonstrates that easily measured functional traits may be used as indicators of fragmentation vulnerability in urban systems allowing generalizations to larger species sets.     

Movements of cactus bugs: Patch transfers,matrix resistance,and edge permeability

Individual movement is a key process affecting the distribution of animals in heterogeneous landscapes. For specialist species in patchy habitat, a central issue is how dispersal distances are related to landscape structure. We compared dispersal distances for cactus bugs (Chelinidea vittiger) on two naturally fragmented landscapes (≤ 4% suitable habitat) with different matrix structures (i.e., vegetation height of nonsuitable habitat between suitable patches). Using mark-release-recapture studies, we determined that most transfers between cactus patches occurred during the mating season. Dispersal distances were reduced by > 50% on the landscape that had reduced structural connectivity due to relatively high matrix structure and low patch density. An experiment with detailed movement pathways demonstrated that greater matrix structure decreased mean step lengths, reduced directionality, and thus decreased net displacement by > 60%. However, habitat edges between two matrix elements that differed substantially in resistance to movement were completely permeable. Therefore, the difference in distributions of dispersal distances between the two landscapes mainly reflected the average resistance of matrix habitat and not the level of matrix heterogeneity per se. Our study highlights the merits of combining estimates of dispersal distances with insights on mechanisms from detailed movement pathways, and emphasizes the difficulty of treating dispersal distances of species as fixed traits independent of landscape structure.     

Habitat heterogeneity and life-history traits influence presettlement distributions of early-successional tree species in a late-successional, hemlock-hardwood landscape

In landscapes dominated by late-successional plant communities, early-successional species may lead a tenuous existence, persisting only as fugitives or relying on refuges in marginal habitats to provide a persistent seed source. The objective of this study was to relate fine-scale distributions of early-successional tree species in hemlock-hardwood forests of northern Wisconsin, USA to potential landscape persistence strategies. A special emphasis was placed on eastern white pine (Pinus strobus), a restoration priority in the region. Witness tree data from nineteenth century US Public Land Survey records (encompassing 40,610?km² and 106,790 trees) were used with modern environmental data to relate species distributions to habitat characteristics. Early-successional tree species had strong positive associations with marginal habitats such as inclusions of sandy soil and margins of lakes, wetlands, and rivers. Marginal habitats occupied ~44 % of the landscape, which may help account for the abundance of early-successional species in our study area relative to other hemlock-hardwood forests. Populations of early-successional species in marginal habitats could also have provided important seed sources for the upland mesic landscape matrix, as >70 % of the landscape was within 200?m of these habitats. The degree to which early-successional species were limited to marginal habitats largely followed predictions based on species life-history characteristics, except that white pine was more common than expected in upland mesic habitats. These findings illustrate the potential importance of landscape heterogeneity for persistence of early-successional species in late-successional forest landscapes and provide baseline information on habitat associations and landscape dynamics that will be useful in restoration efforts.     

Joint effects of habitat configuration and temporal stochasticity on population dynamics

Habitat configuration and temporal stochasticity in the environment are recognized as important drivers of population structure, yet few studies have examined the combined influence of these factors. We developed a spatially explicit simulation model to investigate how stochasticity in survival and reproduction influenced population dynamics on landscapes that differed in habitat configuration. Landscapes ranged from completely contiguous to highly fragmented, and simulated populations varied in mean survival probability (0.2, 0.4, 0.8) and dispersal capacity (1, 3, or 5 cells). Overall, habitat configuration had a large effect on populations, accounting for >80% of the variation in population size when mean survival and dispersal capacity were held constant. Stochasticity in survival and reproduction were much less influential, accounting for <1–14% of the variation in population size, but exacerbated the negative effects of habitat fragmentation by increasing the number of local extinctions in isolated patches. Stochasticity interacted strongly with both mean survival probability and habitat configuration. For example, survival stochasticity reduced population size when survival probability was high and habitat was fragmented, but had little effect on population size under other conditions. Reproductive stochasticity reduced population size irrespective of mean survival and habitat configuration, but had the largest effect when survival probability was intermediate and habitat was well connected. Stochasticity also enhanced the variability of population size in most cases. Contrary to expectations, increasing dispersal capacity did not increase population persistence, because the probability of finding suitable habitat within the dispersal neighborhood declined more for the same level of dispersal capacity when fragmentation was high compared to when it was low. These findings suggest that greater environmental variability, as might arise due to climate change, is likely to compound population losses due to habitat fragmentation and may directly reduce population size if reproductive output is compromised. It may also increase variability in population size.     

Effects of surrounding urbanization on non-native flora in small forest patches

The purpose of our study was to compare the number, proportion, and species composition of introduced plant species in forest patches situated within predominantly forested, agricultural, and urban landscapes. A previous study suggested that agricultural landscape context does not have a large effect on the proportion of introduced species in forest patches. Therefore, our main goal was to test the hypothesis that forest patches in an urban landscape context contain larger numbers and proportions of non-native plant species. We surveyed the vegetation in 44 small remnant forest fragments (3–7.5 ha) in the Ottawa region; 15 were situated within forested landscapes, 18 within agricultural landscapes, and 11 within urban landscapes. Forest fragments in urban landscapes had about 40% more introduced plant species and a 50% greater proportion of introduced plant species than fragments found in the other two types of landscape. There was no significant difference in the number or proportion of introduced species in forest fragments within forested vs. agricultural landscapes. However, the species composition of introduced species differed among the forest patches in the three landscape types. Our results support the hypothesis that urban and suburban areas are important foci for spread of introduced plant species.     

The distribution of plant species in urban vegetation fragments

(1) The presence and absence of 22 plant species of various growth forms and habitat associations were analysed in 423 habitat fragments totalling 10.4 km² in a 268 km² urban and suburban region, in Birmingham, UK. (2) Multivariate logistic regressions were used to assess the effects of patch geometry and quality on the species distributions. Measures of geometry were area, shape (S-factor), distance from open countryside and various measures of isolation from other patches. Potential habitat for each species was determined quantitatively, and the distribution of each species was considered within a subset of patches containing potentially suitable habitat types. There was found to be a significant positive correlation between the density of patches available to a species and the proportion of these patches which were occupied. (3) Logistic analyses and incidence functions revealed that, for many of the species, occupancy increased with site age, area, habitat number and similarity of adjacent habitats, while increasing distance to the nearest recorded population of the same species decreased the likelihood that a species would be found in a patch. (4) Patterns of occupancy are consistent with increased extinction from small sites, and colonisation of nearby habitats, coupled with an important role for site history. We conclude that spatial dynamics at the scale of the landscape are of importance to the long-term persistence of many plant species in fragmented landscapes, and must be seriously considered in conservation planning and management. These results have direct implications for the siting and connectivity of urban habitat reserves.     

What you see is where you go? Modeling dispersal in mountainous landscapes

Inter-patch connectivity can be strongly influenced by topography and matrix heterogeneity, particularly when dealing with species with high cognitive abilities. To estimate dispersal in such systems, simulation models need to incorporate a behavioral component of matrix effects to result in more realistic connectivity measures. Inter-patch dispersal is important for the persistence of capercaillie (Tetrao urogallus) in central Europe, where this endangered grouse species lives in patchy populations embedded in a mountainous landscape. We simulated capercaillie movements with an individual-based, spatially explicit dispersal model (IBM) and compared the resulting connectivity measure with distance and an expert estimation. We used a landscape comprising discrete habitat patches, temporary habitat, non-habitat forests, and non-habitat open land. First, we assumed that dispersing individuals have perfect knowledge of habitat cells within the perceptual range (null model). Then, we included constraints to perception and accessibility, i.e., mountain chains, open area and valleys (three sub-models). In a full model, all sub-models were included at once. Correlations between the different connectivity measures were high (Spearman’s ρ > 0.7) and connectivity based on the full IBM was closer to expert estimation than distance. For selected cases, simple distance differed strongly from the full IBM measure and the expert estimation. Connectivity based on the IBM was strongly sensitive to the size of perceptual range with higher sensitivity for the null model compared to the full model that included context dependent perceptual ranges. Our heuristic approach is adequate for simulating movements of species with high cognitive abilities in strongly structured landscapes that influence perception and permeability.     

Edge-mediated patterns of seed removal in experimentally connected and fragmented landscapes

While biological reserves remain central to biodiversity conservation, the amount of area available for terrestrial reserves may be inadequate for many taxa. Biodiversity spillover—the promotion of diversity in matrix areas surrounding reserves—might help address this shortfall in reserve area. However, the mechanistic underpinning of spillover remains uninvestigated. Two fundamental processes—seed dispersal and establishment—might generate plant biodiversity spillover. Here, we investigate the role of establishment in promoting spillover by assessing post-dispersal seed predation, a key component of establishment, in the matrix of a replicated, large-scale habitat fragmentation experiment, where spillover is elevated around patches connected by landscape corridors. Our results show that matrix seed predation may constrain the distance of this spillover effect by reducing establishment: seed removal was least at the matrix edge and increased further into the matrix. We found some support for matrix seed predation underpinning previously reported landscape-level variation in spillover. Of the three species we investigated, two showed evidence for elevated seed predation in the matrix surrounding the unconnected patches around which the lowest levels of spillover occur. However, seed predation did not explain connectivity-enhanced spillover, suggesting that seed dispersal likely drives this pattern. Management activities that increase seed deposition in the matrix may have beneficial effects via spillover. Our work also illustrates that matrix-mediated gradients in seed predation may be widespread, but likely vary depending upon matrix composition and the ecological system under consideration. In fragmented landscapes, this gradient could impact the distribution, abundance, and spread of plant species.     

The Implications of Metalandscape Connectivity for Population Viabilityin Migratory Songbirds

Landscape connectivity is considered important for species persistence, but linkages among landscape populations (metalandscape connectivity) may be necessary to ensure the long-term viability of some migratory songbirds at a broader regional scale. Because of regional source-sink dynamics, these species can maintain steady populations within extensively fragmented landscapes (landscape sinks) owing to high levels of immigration from source landscapes. We undertook a modeling study to identify the conditions under which immigration, an index of metalandscape connectivity, could rescue declining populations of songbirds in heavily disturbed landscapes. In general, low to moderate levels of immigration (m = 0–20%) were sufficient to rescue species with low edge-sensitivity in landscapes where<70% habitat had been destroyed. At the other extreme, moderate to high levels of immigration (m = 11–40%) were usually required to rescue highly edge-sensitive species in these same landscapes. Very high levels of immigration (m>40%) were required to rescue highly edge-sensitive species in extensively fragmented landscapes that had lost >50% habitat, or when any landscape lost ≥50% habitat gradually over a period of 100 or more years (r = 0.5% habitat lost/year). Paradoxically higher levels of immigration were thus necessary to offset population declines when habitat was lost gradually than when it was lost quickly, where population response lagged behind landscape change. This implies that the importance of metalandscape connectivity for population viability may not be fully appreciated in landscapes undergoing rapid rates of change. Natural immigration rates for migratory songbirds match the very high levels (>40%) we found necessary to sustain populations in heavily disturbed landscapes, which underscores the importance of metalandscape connectivity for the continued persistence of many migratory songbirds in the face of widespread habitat loss and fragmentation.     

Patterns of habitat occupancy, genetic variation and predicted movement of a flightless bush cricket, Pholidoptera griseoaptera, in an agricultural mosaic landscape

Habitat fragmentation has been generally regarded detrimental to the persistence of many species, especially those with limited dispersal abilities. Yet, when exactly habitat elements become functionally disconnected very much depends on the dispersal ability of a species in combination with the landscape’s composition in which it occurs. Surprisingly, for many small and ground-walking generalists knowledge at what spatial scale and to what extent landscape structure affects dispersal is very scarce. Because it is flightless, the bush cricket Pholidoptera griseoaptera may be regarded susceptible to fragmentation. We applied habitat occupancy surveys, population genetic analyses and movement modelling to investigate the performance of P. griseoaptera in an agricultural mosaic landscape with suitable habitat patches of varying size and isolation. Despite its presumed dispersal limitation we could show that P. griseoaptera occupied the majority of suitable habitats, including small and isolated patches, showed a very low and non-significant genetic differentiation (F _ST = 0.0072) and, in the model, managed to colonize around 73% of all suitable habitat patches within one generation under weak and strong landscape-effect scenarios. We conclude that P. griseoaptera possesses the behavioural attributes (frequent inter-patch dispersal) necessary to persist in this landscape characterized by a patchy distribution of habitat elements. Yet, sound recommendations to landscape planning and conservation require more research to determine whether this represents a general behaviour of the species or a behavioural adaptation to this particular landscape.     

Cultural landscapes of Germany are patch-corridor-matrix mosaics for an invasive megaforb

Predicting the vulnerability of landscapes to both the initial colonisation and the subsequent spread of invasive species remains a major challenge. The aim of this study was to assess the relative importance of sub-patch level factors and landscape factors for the invasion of the megaforb Heracleum mantegazzianum. In particular, we tested which factors affect the presence in suitable habitat patches and the cover-percentage within invaded patches. For this purpose, we used standard (logistic) regression modelling techniques. The regression analyses were based on inventories of suitable habitat patches in 20 study areas (each 1 km²) in cultural landscapes of Germany. The cover percentage in invaded patches was independent from landscape factors, except for patch shape, and even unsatisfactorily explained by sub-patch level factors included in the analysis (R ² = 0.19). In contrast, presence of H. mantegazzianum was affected by both local and landscape factors. Woody habitat structure decreased the occurrence probability, whereas vicinity to transport corridors (rivers, roads), high habitat connectivity, patch size and perimeter-area ratio of habitat patches had positive effects. The significance of corridors and habitat connectivity shows that dispersal of H. mantegazzianum through the landscape matrix is limited. We conclude that cultural landscapes of Germany function as patch-corridor-matrix mosaics for the spread of H. mantegazzianum. Our results highlight the importance of landscape structure and habitat configuration for invasive spread. Furthermore, this study shows that both local and landscape factors should be incorporated into spatially explicit models to predict spatiotemporal dynamics and equilibrium stages of plant invasions.     

Species Dynamics in Disturbed Landscapes: When does a Shifting Habitat Mosaic Enhance Connectivity?

Although landscape ecology emphasizes the effects of spatial pattern on ecological processes, most neutral models of species–habitat relationships have treated habitat as a static constraint. Do the working hypotheses derived from these models extend to real landscapes where disturbances create a shifting mosaic? A spatial landscape simulator incorporating vegetation dynamics and a metapopulation model was used to compare species in static and dynamic landscapes with identical habitat amounts and spatial patterns. The main drivers of vegetation dynamics were stand-replacing disturbances, followed by gradual change from early-successional to old-growth habitats. Species dynamics were based on a simple occupancy model, with dispersal simulated as a random walk. As the proportion of available habitat (p) decreased from 1.0, species occupancy generally declined more rapidly and reached extinction at higher habitat levels in dynamic than in static landscapes. However, habitat occupancy was sometimes actually higher in dynamic landscapes than in static landscapes with similar habitat amounts and patterns. This effect was most pronounced at intermediate amounts of habitat (p = 0.3?0.6) for mobile species that had high colonization rates, but were unable to cross non-habitat patches. Differences between static and dynamic landscapes were contingent upon the initial metapopulation size and the shapes of disturbances and the resulting habitat patterns. Overall, the results demonstrate that dispersal-limited species exhibit more pronounced critical behavior in dynamic landscapes than is predicted by simple neutral models based on static landscapes. Thus, caution should be exercised in extending generalizations derived from static landscape models to disturbance-driven landscape mosaics.