Anthropogenic landscape change promotes asymmetric dispersal and limits regional patch occupancy in a spatially structured bird population

1. Local extinctions in habitat patches and asymmetric dispersal between patches are key processes structuring animal populations in heterogeneous environments. Effective landscape conservation requires an understanding of how habitat loss and fragmentation influence demographic processes within populations and movement between populations. 2. We used patch occupancy surveys and molecular data for a rainforest bird, the logrunner (Orthonyx temminckii), to determine (i) the effects of landscape change and patch structure on local extinction; (ii) the asymmetry of emigration and immigration rates; (iii) the relative influence of local and between-population landscapes on asymmetric emigration and immigration; and (iv) the relative contributions of habitat loss and habitat fragmentation to asymmetric emigration and immigration. 3. Whether or not a patch was occupied by logrunners was primarily determined by the isolation of that patch. After controlling for patch isolation, patch occupancy declined in landscapes experiencing high levels of rainforest loss over the last 100 years. Habitat loss and fragmentation over the last century was more important than the current pattern of patch isolation alone, which suggested that immigration from neighbouring patches was unable to prevent local extinction in highly modified landscapes. 4. We discovered that dispersal between logrunner populations is highly asymmetric. Emigration rates were 39% lower when local landscapes were fragmented, but emigration was not limited by the structure of the between-population landscapes. In contrast, immigration was 37% greater when local landscapes were fragmented and was lower when the between-population landscapes were fragmented. Rainforest fragmentation influenced asymmetric dispersal to a greater extent than did rainforest loss, and a 60% reduction in mean patch area was capable of switching a population from being a net exporter to a net importer of dispersing logrunners. 5. The synergistic effects of landscape change on species occurrence and asymmetric dispersal have important implications for conservation. Conservation measures that maintain large patch sizes in the landscape may promote asymmetric dispersal from intact to fragmented landscapes and allow rainforest bird populations to persist in fragmented and degraded landscapes. These sink populations could form the kernel of source populations given sufficient habitat restoration. However, the success of this rescue effect will depend on the quality of the between-population landscapes.     

Patch occupancy and abundance of local populations in landscapes differing in degree of habitat fragmentation: a case study of the colonial black‐headed gull,Chroicocephalus ridibundus

Aim This study investigated whether habitat fragmentation at the landscape level influences patch occupancy and abundance of the black‐headed gull, Chroicocephalus ridibundus, and whether the response of the species to environmental factors is consistent across replicated landscape plots. Location Water bodies (habitat patches) in southern Poland. Methods Surveys were conducted in two landscape types (four plots in each): (1) more‐fragmented landscape, in which habitat patches were small (mean size 2.2–6.2 ha) and far apart (mean distance 2.5–3.1 km); and (2) less‐fragmented landscape, in which habitat patches were large (mean size 9.2–16.5 ha) and separated by short distances (mean 0.9–1.4 km). Observations were performed twice in 284 potential habitat patches during the 2007 breeding season. Results Colonies were significantly more frequent and larger in the less‐fragmented landscapes than in the more‐fragmented ones. Probability of patch occupancy and number of breeding birds were positively related with patch size and these relationships were especially strong in the more‐fragmented landscapes. In the less‐fragmented landscapes, the occurrence of black‐headed gulls was negatively related to the distance to the nearest local population, but in the more‐fragmented landscapes such a relationship was not detected. As distance to the nearest habitat patch increased, the probability of the patch occupancy decreased in the more‐fragmented landscapes. Moreover, abundance was negatively influenced by distance to the nearest habitat patch, especially strongly in more‐fragmented landscapes. Proximity of corridors (rivers) positively influenced the occupation of patches regardless of landscape type. The number of islets positively influenced occupancy and abundance of local populations, and this relationship was stronger in the more‐fragmented landscapes. Main conclusions Our results are in agreement with predictions from metapopulation theory and are the first evidence that populations of black‐headed gulls may have a metapopulation structure. However, patch occupancy and abundance were differentially affected by explanatory variables in the more‐fragmented landscapes than in the less‐fragmented ones. This implies that it is impossible to derive, a priori, predictions about presence/abundance patterns based on only a single landscape.     

The influence of patch demographics on metapopulations, with particular reference to successional landscapes

The classical view of metapopulations relates the regional abundance of a species to the balance between the extinction and colonization dynamics of identical local populations. Species in successional landscapes may represent the most appropriate examples of classical metapopulations. However, Levins‐type metapopulation models do not explicitly separate population loss due to successional habitat change from other causes of extinction. A further complication is that the chance of population loss due to successional habitat change may be related to the age of a patch. I developed simple patch occupancy models to include succession and included consideration of patch age structure to address two related questions: what are the implications of changes in patch demographic rates and when is a move to a structured patch occupancy model justified? Age‐related variation in patch demography could increase or decrease the equilibrium fraction of the available habitat occupied by a species when compared to the predictions of an unstructured model. Metapopulation persistence was enhanced when the age class of patches with the highest species occupancy suffered relatively low losses to habitat succession. Conversely, when the age class of patches with the highest species occupancy also had relatively high successional loss rates, extinction thresholds were higher that would be predicted by a simple unstructured model. Hence age‐related variation in patch successional rate introduces biases into the predictions of simple unstructured models. Such biases can be detected from field surveys of the fraction of occupied and unoccupied patches in each age class. Where a bias is demonstrated, unstructured models will not be adequate for making predictions about the effects of changing parameters on metapopulation size. Thinking in successional terms emphasizes how landscapes might be managed to enhance or reduce the patch occupancy by any particular metapopulation     

Temporal patch occupancy dynamics of the Siberian flying squirrel in a boreal forest landscape

Ability to predict species distribution in a landscape is of crucial importance for natural resource management and species conservation. Therefore, the understanding of species habitat requirements and spatio-temporal dynamics in occurrence is needed. We examined patch occupancy patterns of the Siberian flying squirrel Pteromys volans in northern Finland across a seven year study period. Forest patches dominated by mature spruce ( Picea abies ) in a study area (375 km²) were surveyed to monitor the presence or absence of the flying squirrel. The patch occupancy pattern was dynamic: about half of the habitat patches were occupied at least once during the study period and more patches were colonised than were abandoned. Patches that were continuously occupied (i.e. occupied during all sample periods) were typically of high quality (based on habitat and landscape characteristics), continuously unoccupied patches were usually of low quality, and intermediate quality patches were occupied intermittently. The variables explaining patch occupancy were similar each year, and a statistical model based on data from the year 2000 also predicted occupancy in 2004 with similar accuracy. However, data from a single survey were inadequate for identifying patches used intermittently by flying squirrels. Despite inconsistent occupancy, these patches may be important for the local persistence of flying squirrels. The dynamic occupancy pattern may thus affect estimates of suitable habitat area and identification of functional patch networks for landscape planning. These results emphasise the need for follow-up studies to better understand population patterns and processes in time.     

Interpatch movement of the red milkweed beetle,Tetraopes tetraophthalmus: individual responses to patch size and isolation

Individual movement patterns and the effects of host plant patch size and isolation on patch occupancy were examined for red milkweed beetles, Tetraopes tetraophthalmus, residing in a heterogeneous landscape. Male beetles were found to move both more often and farther between host plant patches than female beetles, and this difference affected the patterns of patch occupancy observed. Overall, unoccupied milkweed patches were smaller and more isolated than patches occupied by beetles. Patches uninhabited by females tended to be more isolated, but not necessarily smaller, than patches with female beetles, indicating that females may be affected more by patch isolation than patch size. Presence of male beetles on patches showed a stronger response to patch size than to patch isolation. Differences in movement between males and females illustrate the need for demographically based dispersal data. Comparisons of Tetraopes interpatch movement patterns between landscapes composed of patches of different size revealed that landscapes with overall smaller patches may have greater rates of interpatch movement.     

Isolation determines patterns of species presence in highly fragmented landscapes

In fragmented landscapes, changes in habitat availability, patch size, shape and isolation may affect survival of local populations. Proposing efficient conservation strategies for such species relies initially on distinguishing the particular effects of those factors. To address these issues, we investigated the occurrence of 3 bird species in fragmented Brazilian Atlantic Forest landscapes. Playback techniques were used to collect presence/absence data of these species inside 80 forest patches, and incidence models were used to infer their occupancy pattern from landscape spatial structure. The relative importance of patch size, shape and surrounding forest cover and isolation was assessed using a model selection approach based on maximum likelihood estimation. The presence of all species was in general positively affected by the amount of surrounding habitat and negatively affected by inter‐patch distances. The joint effects of patch size and the surrounding landscape characteristics were important determinants of occupancy for two species. The third species was affected only by forest cover and mean patch isolation. Our results suggest that local species presence is in general more influenced by the isolation from surrounding forests than by patch size alone. We found evidence that, in highly fragmented landscapes, birds that can not find patches large enough to settle may be able to overcome short distances through the matrix and include several nearby patches within their home‐ranges to complement their resource needs. In these cases, patches must be defined as functionally connected habitat networks rather than mere continuous forest segments. Bird conservation strategies in the Atlantic forest should focus on increasing patch density and connectivity, in order to implement forest networks that reduce the functional isolation between large remnants with remaining core habitat.     

Quantitative predictions for patch occupancy of capercaillie in fragmented habitats

A major conclusion of studying metapopulation biology is that species conservation should favor regional rather than local population persistence. Regional persistence is tightly linked to size, spatial configuration and quality of habitat patches. Hence it is important for the management of endangered species that priority patches can be identified. We developed a predictive model of patch occupancy by capercaillie, a threatened grouse species, based on a single snapshot of data. We used logistic regression to predict patch occupancy as a function of patch size, isolation, connectivity, relative altitude, and biogeographical area. The probability of a patch being occupied increased with patch size and increasing altitude, and decreased with increasing distance to the next occupied patch. Patch size was the most important predictor although occupied patches varied considerably in size. Our model only uses data on the number, size and spatial configuration of habitat patches. It is a useful tool to designate priority areas for conservation, i.e. large core patches with high resilience in habitat quality, smaller island‐patches that still have high probability of being inhabited or becoming recolonised, and patches functioning as “stepping stones”. If capercaillie is to be preserved, habitat suitability needs to be maintained in a functional network of patches that account for size and inter‐patch distance thresholds as found in this study. We suggest that similar area‐isolation relationships are valid for almost any region within the distribution range of capercaillie. The thresholds for occupancy are however likely to depend on characteristics of the respective landscape. The outcome of our study emphasises the need for future investigations that explore the relationship between patch occupancy, matrix quality and its resistance to dispersing individuals.     

The importance of forest patch networks for the conservation of the Thorn-tailed Rayaditos in central Chile

Conservation of forest birds in fragmented landscapes requires not only determining the critical patch characteristics influencing local population persistence but also identifying patch networks providing connectivity and suitable habitat conditions necessary to ensure regional persistence. In this study, we assessed the importance of patch attributes, patch connectivity, and network components (i.e., groups of interconnected patches) in explaining the occupancy pattern of the Thorn-tailed Rayadito (Aphrastura spinicauda), a forest bird species of central Chile. Using a daily movement threshold distance, we identified a total of 16 network components of sclerophyllous forest within the study area. Among those components, patch area and vegetation structure-composition were important predictors of patch occupancy. However, the inclusion of patch connectivity and component size (i.e., the area of a network component) into the models greatly increases the models’ accuracy and parsimony. Using the best-fitted model, a total of 33 patches were predicted to be occupied by rayaditos within the study area, but such occupied patches were distributed in only six network components. These results suggest that persistence of rayaditos in central Chile requires the maintenance of large single patches and patch networks providing habitat and connectivity.     

The larval ecology of the butterfly Euphydryas desfontainii (Lepidoptera: Nymphalidae) in SW-Portugal: food plant quantity and quality as main predictors of habitat quality

Corresponding to theory, the persistence of metapopulations in fragmented landscapes depends on the area of suitable habitat patches and their degree of isolation, mediating the individual exchange between habitats. More recently, habitat quality has been highlighted as being equally important. We therefore assess the role of habitat area, isolation and quality for the occupancy of larval stages of the regionally threatened butterfly Euphydryas desfontainii occurring in grassland habitats comprising the host plant Dipsascus comosus. We put a special focus on habitat quality which was determined on two spatial scales: the landscape (among patches) and the within-patch level. On the landscape level, occupancy of caterpillars was determined by a presence-absence analysis at 28 host plant patches. On the within-patch level, oviposition site selection was studied by comparing 159 host plants with egg clutches to a random sample of 253 unoccupied host plants within six habitat patches. The occupancy of caterpillars and presence of egg clutches on host plants was then related to several predictors such as patch size and isolation on the landscape level and host plant characteristics and immediate surroundings on the within patch level. On the landscape level, only host plant abundance was related to the presence of caterpillars, while size and isolation did not differ between occupied and unoccupied patches. However, the weak discrimination of larval stages among patches changed on the within-patch level: here, several microclimatic predictors such as sunshine hours and topography, host plant morphology and phenology as well as further potential host plants in the immediate surroundings of the plant chosen for oviposition strongly determined the presence of egg clutches. We strongly suggest promoting the presence of the host plant in topographically and structurally rich habitat patches to offer potential for microclimatic compensation for a species considered threatened by climate change.     

Landscape matrix modifies richness of plants and insects in grassland fragments

There is an increasing awareness that not only area and isolation, but also the characteristics of the landscape surrounding habitat patches influence population persistence and species diversity in fragmented landscapes. In this study, we examine the effects of grassland fragmentation and land use in the landscape matrix (on a 2 km scale) on species richness of plants, butterflies, bees and hoverflies. These organisms were studied in replicated remnant patches of different sizes and isolation, embedded in landscapes dominated either by forest, arable land or a mix of these. We found positive effects of patch area on species richness of the three insect taxa, but not of plants. Isolation had a negative effect only on hoverflies. Matrix type had contrasting effects on the studied taxa. Species richness of plants and butterflies was lowest in patches in landscapes dominated by arable land and highest in forest‐dominated landscapes. For hoverflies, the negative effect of small patch area was strongest in forest‐dominated landscapes, and there was a similar non‐significant trend for bees. Our study shows the importance of considering matrix characteristics when studying responses to habitat fragmentation. Differences in matrix response among organism groups probably impinge on differing mechanisms. A forest matrix is likely to provide additional resources for butterflies but either constitute a barrier to dispersal or deprive resources as compared to an arable matrix for hoverflies. Enhanced plant diversity in grassland patches embedded in forested landscapes can be explained by habitat generalists more easily invading these patches, or by an unpaid extinction debt in these landscapes.     

Proximity of restored hedgerows interacts with local floral diversity and species' traits to shape long‐term pollinator metacommunity dynamics

Disconnected habitat fragments are poor at supporting population and community persistence; restoration ecologists, therefore, advocate for the establishment of habitat networks across landscapes. Few empirical studies, however, have considered how networks of restored habitat patches affect metacommunity dynamics. Here, using a 10‐year study on restored hedgerows and unrestored field margins within an intensive agricultural landscape, we integrate occupancy modelling with network theory to examine the interaction between local and landscape characteristics, habitat selection and dispersal in shaping pollinator metacommunity dynamics. We show that surrounding hedgerows and remnant habitat patches interact with the local floral diversity, bee diet breadth and bee body size to influence site occupancy, via colonisation and persistence dynamics. Florally diverse sites and generalist, small‐bodied species are most important for maintaining metacommunity connectivity. By providing the first in‐depth assessment of how a network of restored habitat influences long‐term population dynamics, we confirm the conservation benefit of hedgerows for pollinator populations and demonstrate the importance of restoring and maintaining habitat networks within an inhospitable matrix.     

Young flying squirrels (Pteromys volans) dispersing in fragmented forests

Dispersal is a key determinant of the population dynamics ofspecies. Thus, a better understanding of how dispersal is affectedby the landscape structure and how animals make decisions aboutmoving across different landscapes is needed. We studied thedispersal of 60 radio-collared juvenile Siberian flying squirrels(Pteromys volans) in southern Finland. The effect of landscapestructure on selected dispersal direction, dispersal distance,and straightness of dispersal path was studied. Flying squirrelswere capable of dispersing over long distances in fragmentedforest landscapes. The patches used as temporary roosting sitesduring dispersal were of a lower quality than were those usedas finally occupied patches. The patches used were larger thanwere patches on average in the study areas. There was a veryclear directional bias in the dispersal path (i.e., it was nearlya straight line), which remained over a large scale, but wide-openareas obstructed the straightness of the path. As the distancesbetween crossed patches increased, short-distance disperserswere found further away from their natal home range. However,there were no differences in the landscape that could explainthe differences between individuals in decisions to remain philopatricor to become short- or long-distance dispersers. In addition,whereas short-distance dispersers dispersed in random directions,long-distance dispersers started to disperse in directions dominatedby preferred habitat. Thus, there were behavioral differencesbetween dispersers. Our results supported the hypotheses statingthat individuals decide to disperse long or short distancesbefore the onset of dispersal.     

The relative contribution of local habitat and landscape context to metapopulation processes: a dynamic occupancy modeling approach

Changes in site occupancy across habitat patches have often been attributed to landscape features in fragmented systems, particularly when considering metapopulations. However, failure to include habitat quality of individual patches can mask the relative importance of local scale features in determining distributional changes. We employed dynamic occupancy modeling to compare the strength of local habitat variables and metrics of landscape patterns as drivers of metapopulation dynamics for a vulnerable, high‐elevation species in a naturally fragmented landscape. Repeat surveys of Bicknell's thrush Catharus bicknelli presence/non‐detection were conducted at 88 sites across Vermont, USA in 2006 and 2007. We used an organism‐based approach, such that at each site we measured important local‐scale habitat characteristics and quantified landscape‐scale features using a predictive habitat model for this species. We performed a principal component analysis on both the local and landscape features to reduce dimensionality. We estimated site occupancy, colonization, and extinction probabilities while accounting for imperfect detection. Univariate, additive, and interaction models of local habitat and landscape context were ranked using AICc scores. Both local and landscape scales were important in determining changes in occupancy patterns. An interaction between scales was detected for occupancy dynamics indicating that the relationship of the parameters to local‐scale habitat conditions can change depending on the landscape context and vice versa. An increase in both landscape‐ and local‐scale habitat quality increased occupancy and colonization probability while decreasing extinction risk. Colonization and extinction were both more strongly influenced by local habitat quality relative to landscape patterns. We also identified clear, qualitative thresholds for landscape‐scale features. Conservation of large habitat patches in high‐cover landscapes will help ensure persistence of Bicknell's thrushes, but only if local scale habitat quality is maintained. Our results highlight the importance of incorporating information beyond landscape characteristics when investigating patch occupancy patterns in metapopulations.     

Habitat quality of source patches and connectivity in fragmented landscapes

Because spatial connectivity is critical to dispersal success and persistence of species in highly fragmented landscapes, the way that we envision and measure connectivity is consequential for biodiversity conservation. Connectivity metrics used for predictive modeling of spatial turnover and patch occupancy for metapopulations, such as with Incidence Function Models (IFM), incorporate distances to and sizes of possible source populations. Here, our focus is on whether habitat quality of source patches also is considered in these connectivity metrics. We propose that effective areas (weighted by habitat quality) of source patches should be better surrogates for population size and dispersal potential compared to unadjusted patch areas. Our review of a representative sample of the literature revealed that only 12.5% of studies incorporated habitat quality of source patches into IFM-type connectivity metrics. Quality of source patches generally was not taken into account in studies even if habitat quality of focal patches was included in analyses. We provide an empirical example for a metapopulation of a rare wetland species, the round-tailed muskrat (Neofiber alleni), demonstrating that a connectivity metric based on effective areas of source patches better predicts patch colonization and occupancy than a metric that used simple patch areas. The ongoing integration of landscape ecology and metapopulation dynamics could be hastened by incorporating habitat quality of source patches into spatial connectivity metrics applied to species conservation in fragmented landscapes.     

Assessing habitat quality of farm-dwelling house sparrows in different agricultural landscapes

Having historically been abundant throughout Europe, the house sparrow (Passer domesticus) has in recent decades suffered severe population declines in many urban and rural areas. The decline in rural environments is believed to be caused by agricultural intensification, which has resulted in landscape simplification. We used giving-up densities (GUDs) of house sparrows feeding in artificial food patches placed in farmlands of southern Sweden to determine habitat quality during the breeding season at two different spatial scales: the landscape and the patch scale. At the landscape scale, GUDs were lower on farms in homogeneous landscapes dominated by crop production compared to more heterogeneous landscapes with mixed farming or animal husbandry. At the patch level, feeding patches with a higher predation risk (caused by fitting a wall to the patch to obstruct vigilance) had higher GUDs. In addition, GUDs were positively related to population size, which strongly implies that GUDs reflect habitat quality. However, the increase followed different patterns in homogeneous and heterogeneous landscapes, indicating differing population limiting mechanisms in these two environments. We found no effect of the interaction between patch type and landscape type, suggesting that predation risk was similar in both landscape types. Thus, our study suggests that simplified landscapes constitute a poorer feeding environment for house sparrows during breeding, that the population-regulating mechanisms in the landscapes differ, but that predation risk is the same across the landscape types.     

A simple landscape-scale test of a spatially explicit population model: patch occupancy in fragmented south-eastern Australian forests

The results of a landscape‐scale test of ALEX, a widely used metapopulation model for Population Viability Analysis (PVA), are described. ALEX was used to predict patch occupancy by the laughing kookkaburra and the sacred kingfisher in patches of eucalypt forest in south‐eastern Australia. These predictions were compared to field surveys to determine the accuracy of the model. Predictions also were compared to a “naïve” null model assuming no fragmentation effects.
The naïve null model significantly over‐predicted the number of eucalypt patches occupied by the sacred kingfisher, but the observed patch occupancy was not significantly different from that predicted using ALEX. ALEX produced a better fit to the field data than the naïve null model for the number of patches occupied by the laughing kookaburra. Nevertheless, ALEX still significantly over‐predicted the number of occupied patches, particularly remnants dominated by certain forest types – ribbon gum and narrow‐leaved peppermint. The predictions remained significantly different from observations, even when the habitat quality of these patches was reduced to zero. Changing the rate of dispersal improved overall predicted patch occupancy, but occupancy rates for the different forest types remained significantly different from the field observations. The lack of congruence between field data and model predictions could have arisen because the laughing kookaburra may move between an array of patches to access spatially separated food and nesting resources in response to fragmentation. Alternatively, inter‐specific competition may be heightened in a fragmented habitat. These types of responses to fragmentation are not incorporated as part of traditionally applied metapopulation models. Assessments of predictions from PVA models are rare but important because they can reveal the types of species for which forecasts are accurate and those for which they are not. This can assist the collection of additional empirical data to identify important factors affecting population dynamics.     

Metapopulation theory for fragmented landscapes

We review recent developments in spatially realistic metapopulation theory, which leads to quantitative models of the dynamics of species inhabiting highly fragmented landscapes. Our emphasis is in stochastic patch occupancy models, which describe the presence or absence of the focal species in habitat patches. We discuss a number of ecologically important quantities that can be derived from the full stochastic models and their deterministic approximations, with a particular aim of characterizing the respective roles of the structure of the landscape and the properties of the species. These quantities include the threshold condition for persistence, the contributions that individual habitat patches make to metapopulation dynamics and persistence, the time to metapopulation extinction, and the effective size of a metapopulation living in a heterogeneous patch network.     

Flight morphology corresponds to both surrounding landscape structure and local patch conditions in a highly specialized peatland butterfly (Lycaena epixanthe)

1. Movement mediates the response of populations and communities to landscape and habitat spatial structure, yet movement capability may itself be modified by selection pressures accompanying landscape change. Insect flight morphology can be affected by both the landscape surrounding habitat patches and the distribution of resources within habitat patches. 2. This study investigated the relative influence of local habitat patch conditions and surrounding landscape structure on variation in morphological traits associated with flight in the bog copper (Lycaena epixanthe), a butterfly endemic to temperate Nearctic peatlands. 3. Eight habitat patches were sampled to assess the influence of the surrounding landscape (connectivity of potential habitat and matrix composition) and patch size (an integrated proxy of resource density and spatial distribution) on investment into flight, measured by thorax and abdomen mass, and wing area. 4. The results revealed an effect of both local habitat conditions and landscape structure on flight‐related morphological traits. Increasing forest cover in the surrounding landscape, indicative of increased habitat patch isolation, corresponded with less mobile phenotypes in both sexes. Surrounding landscapes with more water were also generally associated with less mobile phenotypes. Investment into flight was greater in smaller peatlands in which host plant density is higher and more homogeneously distributed. 5. The present study highlights that morphological traits associated with mobility may be responding to both local habitat patch characteristics and surrounding landscape structure. It also supports the hypothesis that local habitat conditions contribute to morphological variation in butterflies.     

Habitat quality and population density drive occupancy dynamics of snowshoe hare in variegated landscapes

The influence of habitat quality and population density on occupancy dynamics may surpass that of traditional metrics of area and isolation, but often this is not considered explicitly in studies of spatially structured populations. In landscapes that are not easily characterized as binary habitat/non‐habitat (e.g. variegated landscapes), this influence may be even more important and occur at both local and landscape levels. It follows that occupancy dynamics may be driven by disparate processes depending on how extinction or colonization relate to habitat quality and population density. We examined the relative influence of area, structural isolation, habitat quality, local population density, and neighborhood population density (i.e. population density in the landscape around a site) on the probability of extinction and colonization of snowshoe hare Lepus americanus across an expansive forest mosaic landscape (encompassing the northern third of Idaho). Habitat quality and population density were highly influential in determining extinction and colonization, whereas patch area and isolation were much less important. Sites with heavier vegetative cover at the site or landscape‐level were more likely to be colonized and less likely to go extinct, and sites with greater local population density in the previous time step had lower probability of extinction. Sites embedded in high density neighborhoods also were less likely to go extinct, but not more likely to be colonized. We found a significant interaction between local and neighborhood population density on extinction in 1 yr, suggesting that the strength of demographic rescue may vary dependent on local site densities. Our results add to a growing literature showing that factors outside of structural metrics of area and isolation are important drivers of occupancy dynamics. Given the multi‐scaled influence of habitat quality and population density on occupancy dynamics, our work also indicates that research on snowshoe hare must extend beyond simply assessing local factors to understand the spatial dynamics of populations.     

Modelling the third dimension: Incorporating topography into the movement rules of an individual-based spatially explicit population model

A wide variety of topographical and environmental elements have been shown or proposed to influence the movement decisions of dispersing animals. Most real landscapes have topographical elements such as hills, valleys and urban developments, which can all act to modify a species’ perceptual range and directly influence movement behaviour. If a visual-based perceptual ability enables a dispersing individual to locate suitable habitat patches at a distance, then it is to be expected that topographical features would act to modify the overall success of this strategy. However, the majority of individual-based Spatially Explicit Population Models (SEPM) employ only two-dimensional landscapes.To investigate the effects of topographical elevation on dispersal patterns, a three-dimensional visual-based perceptual range algorithm was added to the dispersal rules of an individual-based SEPM. To explore the possible influences of a behavioural-based response to topography, an algorithm modelling valley-seeking behaviour was also developed. The performance of both algorithms was compared with that of a two-dimensional visual-based perceptual range algorithm. The overall consequences of dispersal under each algorithm were measured by recording population sizes in a target wood in the centre of a modelled, real landscape.The size of the population in the target wood, modelled using both of the three-dimensional algorithms, exhibited sensitivity to the direction of dispersal in interaction with perceptual range, which differed from that predicted by the two-dimensional approach. Population size was dependant on the spatial configuration of habitat patches and on the topography of the landscape, both of which could guide dispersers either towards or away from the target patch depending on the particular combinations of dispersal directions and perceptual ranges selected. Topography was found to have a greater effect on dispersal at shorter perceptual ranges, and thresholds in the results for all three algorithms suggested the existence of species and landscape dependant optimal perceptual ranges. It is recommended that both topography and topographical-based dispersal-altering algorithms, commensurate with the studied species’ behaviour, be incorporated into the movement rule-base of dispersal simulation models. The modelling of topography and its effects on movement in patchy landscapes are seen as essential ingredients in future landscape planning.