Do Habitat Corridors Influence Animal Dispersal and Colonization in Estuarine Systems?

Studies investigating animal response to habitat in marine systems have mainly focused on habitat preference and complexity. This study is one of the first to investigate the affect of benthic habitat corridors and their characteristics on dispersal and colonization by estuarine macrofuana. In this study, mark-recapture field experiments using artificial seagrass units (ASUs) assessed the effects of seagrass corridors, interpatch distance (5 m vs. 10 m), and the ratio of corridor width to patch width (0.5 m:1 m vs. 0.25 m:1 m) on dispersal of two benthic organisms: the highly mobile grass shrimp, Palaemonetes sp., and the less mobile bay scallop, Argopecten irradians, in two estuarine systems in southeastern North Carolina (NC). The presence of a seagrass corridor, interpatch distance, and corridor width to patch width ratios did not significantly affect shrimp or scallop dispersal to receiver patches. Bay scallop dispersal to receiver patches was significantly higher at one site (Drum Shoals) with relatively high flow, compared to a second site (Middle Marsh) with lower flow. We then examined colonization of estuarine macrofauna to seagrass patches with and without corridors to determine which, if any, taxonomic groups respond positively to corridors at scales of 10 m and over 1 month. Colonization of estuarine macrofauna to seagrass patches was enhanced in the presence of corridors at a relatively large interpatch distance (10 m), which was statistically significant for relatively slow moving polychaete worms. Thus, although benthic habitat corridors may facilitate dispersal of relatively slow moving estuarine animals between otherwise isolated seagrass patches, several common seagrass fauna such as grass shrimp and bay scallops apparently use water currents to rapidly disperse across the seagrass/sand landscape.     

Influence of urban edges on stress in an arboreal mammal: a case study of squirrel gliders in southeast Queensland, Australia

There is growing recognition that ecological research must expand its focus beyond inference based on pattern-process relationships to the direct measurement of ecological and physiological processes. Physiological assessment is important because vertebrates cope with unpredictable and noxious stimuli by initiating a stress response. However, an over-activation of the acute stress response by numerous novel and potentially stressful anthropogenic pressures, including those associated with urban edges, has the potential to generate chronic stress and a greater susceptibility to disease, reduce fecundity and survivorship. An individual??s physiological response to edge habitats with varying degrees of contrast to the adjacent disturbed urban matrix (e.g. major vs. minor roads), may provide insight into their survival likelihood in fragmented urban landscapes. Although demographic changes in wildlife resulting from urbanization have been documented, only recently have physiological consequences been examined. We addressed this problem using a case study of the squirrel glider (Petaurus norfolcensis) in the fragmented urban landscape of southeast Queensland, Australia. Hair samples were used to enable a comparison of hair cortisol levels in individual squirrel gliders, providing an indication of potential stress. We applied a linear mixed-effect modeling approach clustered by patch to quantify the influence of site-level habitat factors and relative abundance comparative to edge contrast on hair cortisol levels. We found that edge type had a strong positive effect on hair cortisol levels; but this depended on the availability of abundant nest hollows at a site. We conclude that individual hair cortisol concentration, providing an index of stress, was lowest in interior habitats and highest in edge habitats adjacent to major roads. Furthermore, gliders occupying low edge contrast habitats adjacent to residential areas and minor roads, and containing abundant tree nest hollows, had low-moderate hair cortisol levels. This highlights the potential importance of these habitats for the conservation of arboreal mammals such as the squirrel glider in urban landscapes.     

Predator activity and predation on songbird nests on forest-field edges in east-central Illinois

We measured the activity of mammalian predators, numbers of singing male songbirds, and predation rates on nests of songbirds (152 natural, open-cup nests and 380 artificial nests) on 38 250 m transects located along various types of forest-field edges in a wildlife management area in east-central Illinois. We then related these variables to each other and to measures of the vegetative structure of our transects that we anticipated might influence predator activity or predation rates on nests of birds characteristic of edge and shrubland habitats. Mammalian predators, particularly raccoons (Procyon lotor), were abundant in the wildlife area and present on all transects surveyed. We did not find significant relationships among the variables we measured. Rather, rates of nest predation were consistently high (>70%) and generally evenly distributed around our study site. Medium-sized, generalist mammalian predators in the midwestern United States reach their highest population densities in fragmented landscapes with abundant edge habitat, particularly agricultural edges. Areas of natural habitat in these landscapes dominated by agriculture may concentrate predators and act as ecological traps for nesting birds because they attract high densities of breeding birds that are subjected to high rates of nest predation.     

Edge effect and matrix influence on the nest survival of an old forest specialist,the Brown Creeper (<Emphasis Type="Italic">Certhia americana</Emphasis>)

Conservation strategies should be based on a solid understanding of processes underlying species response to landscape change. In forests fragmented by agriculture, elevated nest predation rates have been reported in many forest bird species, especially near edges. In intensively-managed forest landscapes, timber harvesting might also be associated with negative edge effects or broader “context” effects on some species when the matrix provides additional resources to their major nest predators. In this study, we hypothesized that proximity to a forest edge and proportion of cone-producing plantations will increase nest predation risk in fragments of relatively undisturbed forest. We focused on the Brown Creeper (Certhia americana), an indicator species of late-seral forests. We compared habitat configuration and composition at four spatial scales (0.14, 0.5, 1 and 2 km) around 54 nests and related daily nest survival rate to the distance to the nearest forest edge, mean patch size of late-seral forest (r = 141 m), proportion of non-forested lands (r = 141 m), density of maintained roads (r = 1 km), proportion of cone-producing spruce plantations (r = 2 km), and year. The best model included distance to the nearest edge and proportion of cone-producing plantations. Distance of nests to the nearest edge was the best individual predictor of daily nest survival. A larger sample of nests showed a significant threshold in distance to the nearest forest edge; nests located at least 100 m away were more likely to fledge young. These results suggest that even in managed forest landscapes, matrix effects can be important and some bird species may exhibit negative edge effects.     

Weak effect of edges on avian nesting success in fragmented and forested landscapes in Ontario,Canada

We studied the effects of anthropogenic edges on predation and parasitism of forest bird nests in an agriculturally fragmented landscape and a continuously forested landscape in Ontario, Canada. Nesting data were collected at 1937 nests across 10 species in the fragmented landscape from 2002–2008, and 464 nests across 4 species in the continuously forested landscape from 2006–2008. Brood parasitism only occurred in the fragmented landscape, and was positively related to the proportion of rural grassland and row crop habitats within 500-m of nests. Daily nest survival was negatively related to the density of roads within 500-m of nests in the fragmented landscape, but was not influenced by distance to anthropogenic edge in either landscape. Predation rates were higher in the fragmented landscape for Ovenbird and Rose-breasted Grosbeak nests, but did not differ between landscapes for Veery and American Redstart nests. Uniformly high predation in the fragmented landscape may be a result of (1) matrix predators that penetrate deep (>300 m) into the forest interior, or (2) the additive effect of forest-dependent and matrix-associated predators that results in high predation pressure in both edge and interior habitats. Further research focused on the identification of nest predators, their population dynamics, and habitat use is required to understand the underlying mechanisms leading to uniformly high nest predation in fragmented landscapes.     

Using an individual-based model to examine the roles of habitat fragmentation and behavior on predator–prey relationships in seagrass landscapes

Seagrasses, which form critical subtidal habitats for marine organisms worldwide, are fragmented via natural processes but are increasingly being fragmented and degraded by boating, fishing, and coastal development. We constructed an individual-based model to test how habitat fragmentation and loss influenced predator–prey interactions and cohort size for a group of settling juvenile blue crabs (Callinectes sapidus Rathbun) in seagrass landscapes. Using results from field studies suggesting that strong top-down processes influence the relationship between cannibalistic blue crab populations and seagrass landscape structure, we constructed a model in which prey (juvenile blue crabs) are eaten by mesopredators (larger blue crabs) which in turn are eaten by top-level predators (e.g., large fishes). In our model, we varied the following parameters within four increasingly fragmented seagrass landscapes to test for their relative effects on cohort size: juvenile blue crab (prey) predator avoidance response, hunting ability of mesopredators and predators, the presence of a top-level predator, and prey settlement routines. Generally, prey cohort size was maximized in the presence of top-level predators and when mesopredators and predators exhibited random searching behavior vs. directed hunting. Cohort size for stationary (tethered) prey was maximized in fragmented landscapes, which corresponds to results from field experiments, whereas mobile prey able to detect and avoid predators had higher survival in continuous landscapes. Prey settlement patterns had relatively small influences on cohort size. We conclude that the effects of seagrass fragmentation and loss on organisms such as blue crabs will depend heavily on behaviors of prey and predatory organisms and how these behaviors change with landscape structure.     

Patterns of bird predation on reptiles in small woodland remnant edges in peri-urban north-western Sydney, Australia

The predator–prey relationship plays an integral role in community structure. In the presence of habitat fragmentation, the dynamic interaction among co-existing species may be disrupted. In this paper we investigated the interaction between small skinks resident in open woodland remnants and the predatory birds that cross-forage between the remnants and the surrounding peri-urban matrix. Skinks were found in significantly fewer numbers in the edge of remnants compared to their core. In contrast, predatory birds were in largest numbers at the edge compared to the core of remnants. We found that there was a strong negative correlation between skink numbers and predatory birds (individually and combined) consistent with higher predation pressure in the edge compared to the core of remnants. Strike rates on decoys that mimicked skinks were also higher in the edge compared to core habitats, consistent with higher predation rates in this edge habitat.     

Using an individual-based model to examine the roles of habitat fragmentation and behavior on predator–prey relationships in seagrass landscapes

Seagrasses, which form critical subtidal habitats for marine organisms worldwide, are fragmented via natural processes but are increasingly being fragmented and degraded by boating, fishing, and coastal development. We constructed an individual-based model to test how habitat fragmentation and loss influenced predator–prey interactions and cohort size for a group of settling juvenile blue crabs (Callinectes sapidus Rathbun) in seagrass landscapes. Using results from field studies suggesting that strong top-down processes influence the relationship between cannibalistic blue crab populations and seagrass landscape structure, we constructed a model in which prey (juvenile blue crabs) are eaten by mesopredators (larger blue crabs) which in turn are eaten by top-level predators (e.g., large fishes). In our model, we varied the following parameters within four increasingly fragmented seagrass landscapes to test for their relative effects on cohort size: juvenile blue crab (prey) predator avoidance response, hunting ability of mesopredators and predators, the presence of a top-level predator, and prey settlement routines. Generally, prey cohort size was maximized in the presence of top-level predators and when mesopredators and predators exhibited random searching behavior vs. directed hunting. Cohort size for stationary (tethered) prey was maximized in fragmented landscapes, which corresponds to results from field experiments, whereas mobile prey able to detect and avoid predators had higher survival in continuous landscapes. Prey settlement patterns had relatively small influences on cohort size. We conclude that the effects of seagrass fragmentation and loss on organisms such as blue crabs will depend heavily on behaviors of prey and predatory organisms and how these behaviors change with landscape structure.

     

Matrix effects on plant-frugivore and plant-predator interactions in forest fragments

Structural features of both habitat remnants and surrounding matrix can be important for explaining plant population dynamics and ecosystem functions in human-impacted landscapes. However, little is known about how the structural features of the adjacent matrix affect biotic interactions and whether such context effects are subject to temporal variations. Using the hawthorn Crataegus monogyna in northern Spain, we studied matrix effects on two sequential plant-animal interactions, frugivory by birds and postdispersal seed predation by rodents. Using Hierarchical Linear Models, we compared the magnitude of both interactions on trees located in two patch types that strongly differed in structural features of the adjacent matrix habitat: patches totally surrounded by a degraded, structurally contrasted pastures (unconnected patches), and trees growing in patches adjacent to a lowly degraded, structurally similar mature forests (connected patches). We compared outcomes for 2005 and 2006, which were years with strong differences in community-wide fruit and seed abundance. Frugivory rate did not differ between patch types in either year, likely related to high mobility of birds. Seed predation rates were higher in unconnected patches than in connected ones, but only in 2005. We conclude that strong interannual fluctuations in resource availability are not rare in temperate systems and that recruitment rates could be frequently reduced within unconnected patches, thus collapsing plant regeneration processes of hawthorn populations. Overall, our results suggest that generalizations about potential effects of the matrix on plant-animal interactions within remnant patches must consider: (1) species-specific habitat responses of the organisms, (2) suitability of neighbouring habitats in terms of food supply, and (3) temporal variations in plant-resource availability for interacting animals.     

Effects of landscape structure on nest predation in roadsides of a midwestern agroecosystem: a multiscale analysis

Nest predation is an important cause of mortality for many bird species, especially in grassland ecosystems where generalist predators have responded positively to human disturbance and landscape fragmentation. Our study evaluated the influence of the composition and configuration of the surrounding landscape on nest predation. Transects consisting of 10 artificial ground nests each were set up in 136 roadsides in six watersheds in south-central Iowa. Nest predation on individual roadside transects ranged from 0 to 100% and averaged 23%. The relationship of landscape structure within spatially-nested landscapes surrounding each roadside transect (within 200, 400, 800, 1200, and 1600 m of the transect line) to nest predation was evaluated by using multiple regression and canonical correlation analyses. The results of this multiscale landscape analysis demonstrated that predation on ground nests was affected by the surrounding landscape mosaic and that nest predators with different-sized home ranges and habitat affinities responded to landscapes in different ways. In general, wooded habitats were associated with greater nest predation, whereas herbaceous habitats (except alfalfa/pasture) either were associated with less nest predation or were not important. Different landscape variables were important at different spatial scales. Whereas some block-cover habitats such as woodland were important at all scales, others such as rowcrops and alfalfa/pasture were important at large scales. Some strip-cover habitats such as gravel roads and paved roads were important at small scales, but others such as wooded roadsides were important at all all scales. Most landscape metrics (e.g., mean patch size and edge density) were important at large scales. Our study demonstrated that the relationships between landscape structure and predator assemblages are complex, thus making efforts to enhance avian productivity in agricultural landscapes a difficult management goal.     

Habitat edge effects alter ant-guard protection against herbivory

Edge effects are among the most important drivers of species interactions in fragmented habitats, but the impacts of edge effects on multitrophic interactions are largely unknown. In this study we assess edge effects on species interactions within an ant–plant mutualistic system—where ants protect plants against herbivory—to determine whether habitat edges alter the amount of protection ants provide. We focus on a single species of myrmecophytic plant, Solanum americanum, and experimentally manipulate ant access to study plants in large-scale fragmented habitat patches at the Savannah River Site National Environmental Research Park, USA. In this system, S. americanum commonly hosts honeydew-producing aphids that are tended by ants, and grasshoppers are the primary herbivores. We measured edge effects on the per-plant abundance of aphids and protective ants as well as the abundance of grasshoppers in each habitat patch, and we evaluated levels of ant protection against herbivory near and far from habitat edges. We found that ants provided significant protection to plants far from edges, where herbivory pressure was highest, despite the fact that aphids and ants were least abundant on these plants. Conversely, ants did not provide significant protection near edges, where herbivory pressure was lowest and aphids and ants were most abundant. We conclude that a strong edge effect on grasshopper abundance was a key factor determining the amount of protection ants provided against herbivory. Future studies of the impacts of habitat fragmentation on ant–plant mutualisms will benefit from studies of ant behavior in response to herbivory threats, and studies of edge effects on other species interactions may also need to consider how species’ behavioral patterns influence the interactions in question.     

Living on the edge: quantifying the structure of a fragmented forest landscape in England

Forest ecosystems have been widely fragmented by human land use, inducing significant microclimatic and biological changes at the forest edge. If we are to rigorously assess the ecological impacts of habitat fragmentation, there is a need to effectively quantify the amount of edge habitat within a landscape, and to allow this to be modelled for individual species and processes. Edge effect may extend only a few metres or as far as several kilometres, depending on the species or process in question. Therefore, rather than attempting to quantify the amount of edge habitat by using a fixed, case-specific distance to distinguish between edge and core, the area of habitat within continuously-varying distances from the forest edge is of greater utility. We quantified the degree of fragmentation of forests in England, where forests cover 10 % of the land area. We calculated the distance from within the forest patches to the nearest edge (forest vs. non-forest) and other landscape indices, such as mean patch size, edge density and distance to the nearest neighbour. Of the total forest area, 37 % was within 30 m and 74 % within 100 m of the nearest edge. This highlights that, in fragmented landscapes, the habitats close to the edge form a considerable proportion of the total habitat area. We then show how these edge estimates can be combined with ecological response functions, to allow us to generate biologically meaningful estimates of the impacts of fragmentation at a landscape scale.     

Island biogeography theory outweighs habitat amount hypothesis in predicting plant species richness in small grassland remnants

Context

The habitat amount hypothesis has rarely been tested on plant communities. It remains unclear how habitat amount affect species richness in habitat fragments compared to island effects such as isolation and patch size.

Objectives

How do patch size and spatial distribution compared to habitat amount predict plant species richness and grassland specialist plant species in small grassland remnants? How does sampling area affect the prediction of spatial variables on species richness?

Methods

We recorded plant species density and richness on 131 midfield islets (small remnants of semi-natural grassland) situated in 27 landscapes in Sweden. Further, we tested how habitat amount, compared to focal patch size and distance to nearest neighbor predicted species density and richness of plants and of grassland specialists.

Results

A total of 381 plant species were recorded (including 85 grassland specialist species). A combination of patch size and isolation was better in predicting both density and richness of species compared to habitat amount. Almost 45% of species richness and 23% of specialist species were explained by island biogeography parameters compared to 19 and 11% by the amount of habitat. A scaled sampling method increased the explanation level of island biogeography parameters and habitat amount.

Conclusions

Habitat amount as a concept is not as good as island biogeography to predict species richness in small habitats. Priority in landscape planning should be on larger patches rather than several small, even if they are close together. We recommend a sampling area scaled to patch size in small habitats.

     

Habitat connectivity and complexity underpin fish community structure across a seascape of tropical macroalgae meadows

Context

In heterogeneous landscapes, local patterns of community structure are a product of the habitat size and condition within a patch interacting with adjacent habitat patches of varying composition and quantity. While evidence for local versus landscape factors have been found in terrestrial biomes, support for such multi-scale effects shaping marine ecological communities is equivocal.

Objectives

We investigated whether within-patch habitat condition can override seascape context to explain the community structure of macroalgae-associated reef fishes across a tropical seascape.

Methods

We mapped the distribution and abundance of a diverse family of reef fishes (Labridae) occupying macroalgae meadows within a tropical reef ecosystem, and using best-subsets model selection, investigated the potential for habitat structural connectivity and/or local habitat quality for predicting variations in fish community structure across the seascape.

Results

Local habitat quality (canopy structure, hard habitat complexity) and area of coral-dominated habitat within 500 m of a macroalgal meadow provided the best predictors of fish community structure. However, the specific importance of a given predictor varied with fish life history stage and functional trophic group. Interestingly, macroalgae meadow area was among the least important predictors.

Conclusions

Given the complex interplay between local habitat quality and spatial context effects on fish biodiversity, our study reveals the multi-scale predictors that should be used in spatial conservation and management approaches for tropical fish diversity. Moreover, our findings question the ubiquity of habitat area effects in patchy landscapes, and cautions against a sole reliance on habitat quantity in spatial management.

     

Metapopulation dynamics and a landscape approach to conservation of lowland water voles (<Emphasis Type="Italic">Arvicola amphibius</Emphasis>)

Effective conservation management for species that function as metapopulations requires an understanding of population dynamics at the landscape scale. The water vole, Arvicola amphibius, is one such species. Water voles have recently undergone a significant decline in the UK, as a result of habitat loss and predation from the introduced American mink, Neovison vison. Large reed bed and grazing marsh sites can provide refuge habitats for water voles from mink predation, in which case populations within these sites could sustain metapopulations in the surrounding landscape where conditions are less favourable. We carried out a study using a stochastic patch occupancy model to determine the long term viability of water vole metapopulations in the wider landscape around a series of extensive reed bed and grazing marsh sites designated as National Key Sites for water voles. The results of our model simulations show that a large protected core site, or mainland, is essential in maintaining the long term viability of these systems. Our results also show how these metapopulations could be enhanced by increasing patch numbers through habitat creation and/or restoration and suggest what the minimum effective size of created or restored patches should be. The study shows how population modelling can provide insight into some effective practical ways of enhancing the viability of water vole metapopulations at the landscape scale. Furthermore it demonstrates that extensive wetlands are an appropriate focus for water vole conservation measures.     

On the seasonal effect of landscape structure on a bird species: the thorn-tailed rayadito in a relict forest in northern Chile

Forest bird species exhibit noticeable seasonal behavioral changes that might lead to contrasting effects of landscape pattern upon species abundance and performance. We assessed if the effect of patch and habitat attributes on the landscape use of thorn-tailed rayaditos (Aphrastura spinicauda), a forest bird in a relict patchy forest in northern Chile, varied temporally in association with changes in the behavior of individuals linked to breeding vs. non-breeding conditions. We also assessed the relationship between nest success and patch and habitat attributes, as nest success might be associated to the density rayaditos during the breeding season. We found that density of rayaditos was affected by patch size and functional connectivity but not by habitat structure and that the magnitude of the effect of patch size was greater during the non-breeding season, thus supporting the existence of a temporally variable effect of landscape pattern. Similarly, the nest success of rayaditos was positively affected by functional connectivity and negatively by structural connectivity. We hypothesize that these results emerged from the interaction among territorial behavior, resource limitation and predation risk. Despite the variable intensity of the effect of patch size upon density, however, this landscape attribute, in addition to connectivity, is essential for the persistence of rayaditos at this relict patchy forest landscapes.     

Exploring habitat patch clusters based on network community detection to identify restored priority areas of ecological networks in urban areas

Ecological connectivity is the foundation of maintaining urban biodiversity and ecosystem health. Identifying and managing ecological (connectivity) networks can help maintain the stability of urban ecosystems. However, few studies have explored the cluster effect in the ecological network caused by the imbalance in connectivity strength between habitat patches, which is not conducive to the in-depth restoration of ecological networks. In the present study, a typical urban area, Shenzhen, was used as an example to analyze the important habitats in the city based on the focal species and to identify an ecological network. Habitat patch clusters in the ecological network were explored based on random walk network community detection. These are clusters of closely connected habitat lands. Finally, we analyzed existing urban policies for the protection of clusters and the points to be repaired in the network. The results showed that 50 ecological corridors connected 39 habitats in the study area, which further formed seven habitat patch clusters. Most of the clusters were well-protected by existing policies. Nineteen barrier points were identified between the clusters, and their restoration helped strengthen the connectivity between clusters. This study provides a reference for future urban ecological restoration.     

Habitat effect on vegetation ecology and occurrence on urban masonry walls

Cities contain a diverse range of habitats that support plant establishment and persistence. This study focuses on a particular vertical artificial habitat: masonry retaining walls in Hong Kong. We explored the diversity and co-existence of different plant growth forms, synoptic assessment of habitat conditions, and relationship between habitat factors and vegetation occurrence. Some 270 walls with notable plant colonization in old districts were studied. We surveyed intrinsic wall fabric, extrinsic site condition, tree species and abundance, and other types of plant cover. The data were evaluated with the help of principal component and multiple regression analyses. A wide assemblage of species and growth forms have established spontaneously on walls. The tree flora is dominated by Moraceae (Mulberry family) members, genus Ficus (figs or banyans), and particularly Ficus microcarpa. Trees with strangler characteristics pre-adapted to grow on the vertical habitat are strongly favoured, followed by ruderals and garden escapees. Natives outnumber exotics by a large margin. Multiple wall attributes could be condensed into four factors, classified as water-nutrient supply, habitat connectivity, structure-maintenance, and habitat size. The action of habitat factors on vegetation occurrence hinges on plant growth form and dimension. The occurrence of diminutive lichen-moss is related to the fundamental sustenance water-nutrient factor. The bigger mature trees are more dependent on the larger-scale habitat size factor. The medium-sized plants, including herbs, shrubs and tree seedlings, are contingent upon the dual influence of water-nutrient and habitat connectivity. Spatial contiguity with natural ecosystem can secure continual supplies of seeds, water, nutrient, genial microclimate, and clean air to foster wall vegetation growth. The conservation of walls and their companion flora could avoid degrading or reducing these critical enabling factors. The urban ecological heritage deserves to be protected from unnecessary, misinformed and harmful impacts.     

Edge geometry influences patch-level habitat use by an edge specialist in south-eastern Australia

We investigated patterns in habitat use by the noisy miner (Manorina melanocephala) along farmland-woodland edges of large patches of remnant vegetation (>300 ha) in the highly fragmented box-ironbark woodlands and forests of central Victoria, Australia. Noisy miners exclude small birds from their territories, and are considered a significant threat to woodland bird communities in the study region. Seventeen different characteristics of edge habitat were recorded, together with the detection or non-detection of noisy miners along 129 500-m segments of patch edge. Habitat characteristics ranged from patch-level factors related to patch-edge geometry to site-level floristic factors. Backward (stepwise) logistic regression analyses were used to identify habitat characteristics that were associated with the occupancy of a site by noisy miners. After accounting for the effects of spatial autocorrelation on the occurrence of noisy miners along edges, we identified projections of remnant vegetation from the patch edge into the agricultural matrix (e.g., corners of patches, peninsulas of vegetation) and clumps of trees in the agricultural matrix within 100 m of the edge as significant predictors of the occupancy of edges by noisy miners. This relationship was also confirmed in two other geographically and floristically distinct habitats within Victoria. The use of edges with projections by noisy miners may confer advantages in interspecific territorial defence. In light of these results, we advocate revegetation strategies that attempt to enclose projections within 100 m of the edge, with fencing placed out to this new boundary, to reduce the likelihood of colonisation and domination of an edge by noisy miners. Our study highlights the need for greater consideration to be given to the patterns in habitat use by aggressive edge specialists, particularly in relation to patch-edge geometry and other human-induced components of landscapes.     

Identifying functionally connected habitat compartments with a novel regionalization technique

Landscape ecologists have increasingly turned to the use of landscape graphs in which a landscape is represented as a set of nodes (habitat patches) connected by links representing inter-patch-dispersal. This study explores the use of a graph-based regionalization method, Graph-based REgionalization with Clustering And Partitioning (GraphRECAP), to detect structural groups of habitat patches (compartments) in a landscape graph such that the connections (i.e. the movement of individual organisms) within the groups are greater than those across groups. Specifically, we mapped compartments using habitat and dispersal data for ring-tailed lemurs (Lemur catta) in an agricultural landscape in southern Madagascar using both GraphRECAP and the widely-used Girvan and Newman method. Model performance was evaluated by comparing compartment characteristics and three measures of network connectivity and traversability: the connection strength of habitat patches in the compartments (modularity), the potential ease of individual organism movements (Harary index), and the degree of alternative route presence (Alpha index). Compartments identified by GraphRECAP had stronger within-compartment connections, greater traversability, more alternative routes, and a larger minimum number of habitat patches within compartments, all of which are more desirable traits for ecological networks. Our method could thus facilitate the study of ecosystem resilience and the design of nature reserves and landscape networks to promote the landscape-scale dispersal of species in the fragmented habitats.