Are hedgerows effective corridors between fragments of woodland habitat? An evidence-based approach

Anthropogenic modification of the countryside has resulted in much of the landscape consisting of fragments of once continuous habitat. Increasing habitat connectivity at the landscape-scale has a vital role to play in the conservation of species restricted to such remnant patches, especially as species may attempt to track zones of habitat that satisfy their niche requirements as the climate changes. Conservation policies and management strategies frequently advocate corridor creation as one approach to restore connectivity and to facilitate species movements through the landscape. Here we examine the utility of hedgerows as corridors between woodland habitat patches using rigorous systematic review methodology. Systematic searching yielded 26 studies which satisfied the review inclusion criteria. The empirical evidence currently available is insufficient to evaluate the effectiveness of hedgerow corridors as a conservation tool to promote the population viability of woodland fauna. However, the studies did provide anecdotal evidence of positive local population effects and indicated that some species use hedgerows as movement conduits. More replicated and controlled field investigations or long-term monitoring are required in order to allow practitioners and policy makers to make better informed decisions about hedgerow corridor creation and preservation. The benefits of such corridors in regard to increasing habitat connectivity remain equivocal, and the role of corridors in mitigating the effects of climate change at the landscape-scale is even less well understood.     

Incidence of competitors and landscape structure as predictors of woodland-dependent birds

Globally, modification of landscapes for agriculture has had a strong influence on the distribution and abundance of biota. In particular, woodland-dependent birds are under threat across agricultural landscapes in Britain, North America and Australia, with their decline and extirpation attributed to the loss and fragmentation of habitat. Other native species have become over-abundant in response to anthropogenic landscape change and have strong interactive effects on avian assemblage structure. In eastern Australia, the hyper-aggressive noisy miner (Manorina melanocephala) often dominates woodlands in agricultural landscapes through interspecific competition, resulting in declines of species richness of woodland-dependent birds. We aimed to determine the relative influence and importance of interspecific competition, in situ habitat structure and landscape structure for woodland-dependent bird species at the landscape level. We recorded species-specific landscape incidence of woodland-dependent birds in 24 agricultural-woodland mosaics (25 km²) in southern Queensland, Australia. We selected extensively cleared landscapes (10–23 % woodland cover) where fragmentation effects are expected to be greatest. We applied generalised linear models and hierarchical partitioning to quantify the relative importance of the landscape-level incidence of the noisy miner, mistletoe abundance, shrub cover, woodland extent, woodland subdivision and land-use intensity for the incidence of 46 species of woodland birds at the landscape-scale. The landscape-level incidence of the noisy miner was the most important explanatory variable across the assemblage. Both in situ habitat structure and landscape structure were of secondary importance to interspecific aggression, although previous research suggests that the increasing incidence of the noisy miner in fragmented agricultural landscapes is itself a consequence of anthropogenic changes to landscape structure. Species’ responses to fragmentation varied from positive to negative, but complex habitat structure had a consistently positive effect, suggesting in situ restoration of degraded habitats could be a conservation priority. Landscape wide conservation of woodland-dependent bird populations in agricultural landscapes may be more effective if direct management of noisy miner populations is employed, given the strong negative influence of this species on the incidence of woodland-dependent birds among landscapes.     

Habitat amount and quality,not patch size,determine persistence of a woodland-dependent mammal in an agricultural landscape

Context

The classical theory of island biogeography explains loss of species in fragmented landscapes as an effect of remnant patch size and isolation. Recently this has been challenged by the habitat amount and habitat continuum hypotheses, according to which persistence in modified landscapes is related to total habitat amount rather than habitat configuration or the ability of species to use all habitats to varying degrees. Distinguishing between these theories is essential for effective conservation planning in modified landscapes.

Objective

Identify which factors of habitat type, amount and configuration predict the persistence of a keystone woodland specialist, the eastern bettong Bettongia gaimardi, in a fragmented landscape.

Method

In the Midlands region of Tasmania we carried out camera surveys at 62 sites in summer and winter. We included habitat and landscape features to model whether habitat amount or patch size and isolation influenced the presence of the eastern bettong, and to measure effects of habitat quality.

Results

Habitat amount within a 1 km buffer was a better predictor of occupancy than patch size and isolation. Occupancy was also affected by habitat quality, indicated by density of regenerating stems.

Conclusion

Our results support the habitat amount hypothesis as a better predictor of presence. For a species that is able to cross the matrix between remnant patches and utilise multiple patches, the island biogeography concept does not explain habitat use in fragmented landscapes. Our results emphasize the value of small remnant patches for conservation of the eastern bettong, provided those patches are in good condition.

     

Integration by case,place and process: transdisciplinary research for sustainable grazing in the Lachlan River catchment,Australia

In a context of global agricultural intensification, integrating conservation and agricultural production is a major challenge. We have tackled the problem using a transdisciplinary research framework. Our work focuses on part of the upper Lachlan River catchment in southeastern Australia. The region is dominated by livestock grazing, and is part of an internationally recognised threatened ecoregion because most native woodland vegetation has been cleared. In productive areas, most remnant vegetation occurs as scattered and isolated paddock trees, which are dying from old age and not regenerating due to agricultural practices. The policy context and industry trends present additional risks for sparse trees. These declining trees provide many ecosystem services, including enhanced water infiltration, shade for livestock, aesthetic and cultural values, and habitat for native species. Our research aims to identify management options and policy settings that enable landscape-scale tree regeneration while maintaining grazing production. Our findings highlight tensions between the trajectory of tree cover in the region and stakeholder values. Under status quo management, many scattered and isolated paddock trees will be lost from farms, although most farmers would like to see them persist. Case studies on selected farms reveal management strategies that may be more sustainable in terms of tree regeneration and agricultural productivity, such as rotational grazing. In addition to these applied insights, our work provides a case study illustrating how a transdisciplinary study can be conducted efficiently by a small team. Our pragmatic approach has successfully combined targeted disciplinary activities with strategic collaborations and stakeholder engagement, all united by shared landscape, case graziers, and outreach activities.     

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.     

Targeting and evaluating biodiversity conservation action within fragmented landscapes: an approach based on generic focal species and least-cost networks

The focus of biodiversity conservation is shifting to larger spatial scales in response to habitat fragmentation and the need to integrate multiple landscape objectives. Conservation strategies increasingly incorporate measures to combat fragmentation such as ecological networks. These are often based on assessment of landscape structure but such approaches fail to capitalise on the potential offered by more ecologically robust assessments of landscape function and connectivity. In this paper, we describe a modelling approach to identifying functional habitat networks and demonstrate its application to a fragmented landscape where policy initiatives seek to improve conditions for woodland biodiversity including increasing woodland cover. Functional habitat networks were defined by identifying suitable habitat and by modelling connectivity using least-cost approaches to account for matrix permeability. Generic focal species (GFS) profiles were developed, in consultation with stakeholders, to represent species with high and moderate sensitivity to fragmentation. We demonstrated how this form of analysis can be used to aid the spatial targeting of conservation actions. This ‘targeted’ action scenario was tested for effectiveness against comparable scenarios, which were based on random and clumped actions within the same landscape. We tested effectiveness using structural metrics, network-based metrics and a published functional connectivity indicator. Targeting actions within networks resulted in the highest mean woodland area and highest connectivity indicator value. Our approach provides an assessment of landscape function by recognising the importance of the landscape matrix. It provides a framework for the targeting and evaluation of alternative conservation options, offering a pragmatic, ecologically-robust solution to a current need in applied landscape ecology.     

Scale-dependent importance of environment, land use and landscape structure for species richness and composition of SE Norwegian modern agricultural landscapes

Knowledge of variation in vascular plant species richness and species composition in modern agricultural landscapes is important for appropriate biodiversity management. From species lists for 2201 land-type patches in 16 1-km² plots five data sets differing in sampling-unit size from patch to plot were prepared. Variation in each data set was partitioned into seven sources: patch geometry, patch type, geographic location, plot affiliation, habitat diversity, ecological factors, and land-use intensity. Patch species richness was highly predictable (75% of variance explained) by patch area, within-patch heterogeneity and patch type. Plot species richness was, however, not predictable by any explanatory variable, most likely because all studied landscapes contained all main patch types – ploughed land, woodland, grassland and other open land – and hence had a large core of common species. Patch species composition was explained by variation along major environmental complex gradients but appeared nested to lower degrees in modern than in traditional agricultural landscapes because species-poor parts of the landscape do not contain well-defined subsets of the species pool of species-rich parts. Variation in species composition was scale dependent because the relative importance of specific complex gradients changed with increasing sampling-unit size, and because the amount of randomness in data sets decreased with increasing sampling-unit size. Our results indicate that broad landscape structural changes will have consequences for landscape-scale species richness that are hard or impossible to predict by simple surrogate variables.     

Habitat specificity of patches in modern agricultural landscapes

Habitat specificity analysis provides a tool for partitioning landscape species diversity on landscape elements by separating patches with many rare specialist species from patches with the same number of species, all of which are common generalists and thus provide information of relevance to conservation goals at regional and national levels. Our analyses were based upon species data from 2201 patch elements in SE Norwegian modern agricultural landscapes. The context used for measuring habitat specificity strongly influences the results. In general the gamma diversity contribution and core habitat specificity calculated from the patch data set were correlated. High values for both measures were observed for woodland, pastures and road verges whereas midfield islets and boundary transitional types were ranked low, as opposed to findings in traditional, extensively managed agricultural landscapes. This is due to our study area representing intensively used agricultural landscape elements holding a more trivial species composition, in addition to ruderals being favoured by fertility and disturbance, a finding also being supported by the semi-natural affiliation index. Results obtained by use of checklist data from the same study area diverged from patch data. Caution is needed in interpretation of habitat specificity results obtained from checklist data, because modern agricultural landscapes contain several land types which are seldom surveyed by botanists, thus being under-represented in the data set. We propose the use of core habitat specificity and gamma diversity contribution in parallel to obtain a value neutral diversity assessment that addresses patch uniqueness and other properties of conservation interests.     

Predicting carnivore occurrence with noninvasive surveys and occupancy modeling

Terrestrial carnivores typically have large home ranges and exist at low population densities, thus presenting challenges to wildlife researchers. We employed multiple, noninvasive survey methods—scat detection dogs, remote cameras, and hair snares—to collect detection–nondetection data for elusive American black bears (Ursus americanus), fishers (Martes pennanti), and bobcats (Lynx rufus) throughout the rugged Vermont landscape. We analyzed these data using occupancy modeling that explicitly incorporated detectability as well as habitat and landscape variables. For black bears, percentage of forested land within 5 km of survey sites was an important positive predictor of occupancy, and percentage of human developed land within 5 km was a negative predictor. Although the relationship was less clear for bobcats, occupancy appeared positively related to the percentage of both mixed forest and forested wetland habitat within 1 km of survey sites. The relationship between specific covariates and fisher occupancy was unclear, with no specific habitat or landscape variables directly related to occupancy. For all species, we used model averaging to predict occurrence across the study area. Receiver operating characteristic (ROC) analyses of our black bear and fisher models suggested that occupancy modeling efforts with data from noninvasive surveys could be useful for carnivore conservation and management, as they provide insights into habitat use at the regional and landscape scale without requiring capture or direct observation of study species.     

The influence of habitat availability and landscape structure on the distribution of wood cricket (Nemobius sylvestris) on the Isle of Wight, UK

Little information is available regarding the landscape ecology of woodland invertebrate species with limited dispersal ability. An investigation was therefore conducted within woodland fragments in an agricultural landscape for the flightless wood cricket (Nemobius sylvestris) on the Isle of Wight, UK. The current pattern of distribution of the species, established during a field survey, was related to measures of habitat availability and habitat isolation/fragmentation. Results revealed that wood cricket populations were patchily distributed and mainly found in relatively large mature woodland fragments situated closely (<50 m) to another occupied site. Although the occurrence of wood cricket was related to fragment area, isolation, habitat availability and woodland age, a logistic regression model revealed that presence of the species was most accurately predicted by fragment isolation and area alone. These results highlight the vulnerability of relatively immobile woodland invertebrate species, such as wood cricket, to the impacts of habitat loss and fragmentation.     

Comparative influence of isolation,landscape, and wetland characteristics on egg-mass abundance of two pool-breeding amphibian species

The distribution and abundance of species are shaped by local and landscape processes, but the dominant processes may differ with scale and increasing human disturbance. We investigated population responses of two pool-breeding amphibian species to differences in local and landscape characteristics in suburbanizing, southeastern New Hampshire, USA. In 2003 and 2004, we sampled 49 vernal pools for spotted salamander (Ambystoma maculatum) and wood frog (Lithobates sylvaticus) egg masses. Using egg masses as a proxy for breeding-female population size, we examined the relative influence of five land-use and three isolation variables at two scales (300 and 1000 m) and five wetland variables on egg-mass abundance. For both species, road density at the landscape scale (1000 m) and hydroperiod most strongly predicted egg-mass abundance, with abundance decreasing as roads became denser and hydroperiods shortened. Wetland isolation was also an important predictor, with abundance greatest at more isolated pools, suggesting that both species concentrate at isolated pools when alternative breeding sites are scarce. Surprisingly, no 300-m parameters were strongly associated with salamander egg-mass abundance, whereas several landscape parameters were. In suburbanizing areas, it is at least as important to consider landscape-scale road density as to consider hydroperiod when designing conservation plans for these species. Furthermore, both isolated and clustered pools provide these species important habitat and may require protection. Finally, the conceptual framework for spotted-salamander management must be expanded so that spatial configuration at the landscape scale becomes a regular, integrated component of conservation planning for this species.     

Wetland hydrology,area, and isolation influence occupancy and spatial turnover of the painted turtle, <Emphasis Type="Italic">Chrysemys picta</Emphasis>

Habitat area and isolation have been useful predictors of species occupancy and turnover in highly fragmented systems. However, habitat quality also can influence occupancy dynamics, especially in patchy systems where habitat selection can be as important as stochastic demographic processes. We studied the spatial population dynamics of Chrysemys picta (painted turtle) in a network of 90 wetlands in Illinois, USA from 2007 to 2009. We first evaluated the relative influence of metapopulation factors (area, isolation) and habitat quality of focal patches on occupancy and turnover. Next, we tested the effect of habitat quality of source patches on occupancy and turnover at focal patches. Turnover was common with colonizations (n = 16) outnumbering extinctions (n = 10) between the first 2 years, and extinctions (n = 16) outnumbering colonizations (n = 3) between the second 2 years. Both metapopulation and habitat quality factors influenced C. picta occupancy dynamics. Colonization probability was related positively to spatial connectivity, wetland area, and habitat quality (wetland inundation, emergent vegetation cover). Extinction probability was related negatively to wetland area and emergent vegetation cover. Habitat quality of source patches strongly influenced initial occupancy but not turnover patterns. Because habitat quality for freshwater turtles is related to wetland hydrology, a change from drought to wet conditions during our study likely influenced distributional shifts. Thus, effects of habitat quality of source and focal patches on occupancy can vary in space and time. Both metapopulation and habitat quality factors may be needed to understand occupancy dynamics, even for species exhibiting patchy population structures.     

Habitat corridors and the conservation of small mammals in a fragmented forest environment

At Naringal in south-western Victoria, Australia, clearing of the original forest environment has created an agricultural landscape dominated by grazed pastures of introduced grasses. Remnant forest vegetation is re-stricted to small patches of less than 100 ha in size, that are loosely linked by narrow forested strips along road reserves and creeks. Six native and two introduced species of small terrestrial mammal (< 2 kg) occur within this environment. The native mammals, being dependent upon forest vegetation, were less tolerant to forest fragmentation than were the introduced species that also persist in farmland and farm buildings. The native mammals displayed an increasing frequency of occurrence in successively larger size-classes of forest patches. Those species with the greatest body-weight were the most vulnerable to habitat loss. All species of small mammal occurred in narrow habitat corridors of forest vegetation on roadsides. The resident status, seasonal variation in relative abundance, patterns of reproduction, and movements of each species were monitored in two habitat corridors during a 25-month trapping study. The corridors were found to facilitate continuity between otherwise-isolated populations of small mammals in this locality in two ways: firstly, by providing a pathway for the dispersal of single animals between patches; and secondly, by enabling gene flow through populations resident within the corridors. The small size of forest remnants at Naringal, and the vulnerability of species with low population sizes, emphasize the importance of preserving a mosaic of numerous habitat patches that together will support regional populations of sufficient size for longer-term persistence. The continuity between remnant habitats that is provided by a network of habitat corridors is an essential, and critical, component of this conservation strategy.     

Combined effects of area,connectivity, history and structural heterogeneity of woodlands on the species richness of hoverflies (Diptera: Syrphidae)

Context

Hoverflies are often used as bio-indicators for ecosystem conservation, but only few studies have actually investigated the key factors explaining their richness in woodlands.

Objectives

In a fragmented landscape in southwest France, we investigated the joint effects of woodland area, structural heterogeneity, connectivity and history on the species richness of forest-specialist hoverflies, and whether there was a time lag in the response of hoverflies to habitat changes, and tested the effect of spatiotemporal changes.

Methods

Current species richness was sampled in 48 woodlands using 99 Malaise traps. Structural variables were derived from a rapid habitat assessment protocol. Old maps and aerial photographs were used to extract past and present spatial patterns of the woodlands since 1850. Relationships between species richness and explanatory variables were explored using generalized linear models.

Results

We show that current habitat area, connectivity, historical continuity and the average density of tree-microhabitats explained 35 % of variation in species richness. Species richness was affected differently by changes in patch area between 1979 and 2010, depending on woodland connectivity. In isolated woodlands, extinction debt and colonization credit were revealed, showing that even several decades are not sufficient for hoverflies to adapt to landscape-scale habitat conditions.

Conclusions

These findings emphasise the importance of maintaining connectedness between woodlands, which facilitates the dispersion in a changing landscape. Our results also highlight the benefits of using a change-oriented approach to explain the current distribution patterns of species, especially when several spatial processes act jointly.

     

How should we measure landscape connectivity?

The methods for measuring landscape connectivity have never been compared or tested for their responses to habitat fragmentation. We simulated movement, mortality and boundary reactions across a wide range of landscape structures to analyze the response of landscape connectivity measures to habitat fragmentation. Landscape connectivity was measured as either dispersal success or search time, based on immigration into all habitat patches in the landscape. Both measures indicated higher connectivity in more fragmented landscapes, a potential for problematic conclusions for conservation plans. We introduce cell immigration as a new measure for landscape connectivity. Cell immigration is the rate of immigration into equal-sized habitat cells in the landscape. It includes both within- and between-patch movement, and shows a negative response to habitat fragmentation. This complies with intuition and existing theoretical work. This method for measuring connectivity is highly robust to reductions in sample size (i.e., number of habitat cells included in the estimate), and we hypothesize that it therefore should be amenable to use in empirical studies. The connectivity measures were weakly correlated to each other and are therefore generally not comparable. We also tested immigration into a single patch as an index of connectivity by comparing it to cell immigration over the landscape. This is essentially a comparison between patch-scale and landscape-scale measurement, and revealed some potential for patch immigration to predict connectivity at the landscape scale. However, this relationship depends on the size of the single patch, the dispersal characteristics of the species, and the amount of habitat in the landscape. We conclude that the response of connectivity measures to habitat fragmentation should be understood before deriving conclusions for conservation management.     

Landscape effects on mallard habitat selection at multiple spatial scales during the non-breeding period

Previous studies that evaluated effects of landscape-scale habitat heterogeneity on migratory waterbird distributions were spatially limited and temporally restricted to one major life-history phase. However, effects of landscape-scale habitat heterogeneity on long-distance migratory waterbirds can be studied across the annual cycle using new technologies, including global positioning system satellite transmitters. We used Bayesian discrete choice models to examine the influence of local habitats and landscape composition on habitat selection by a generalist dabbling duck, the mallard (Anas platyrhynchos), in the midcontinent of North America during the non-breeding period. Using a previously published empirical movement metric, we separated the non-breeding period into three seasons, including autumn migration, winter, and spring migration. We defined spatial scales based on movement patterns such that movements >0.25 and <30.00 km were classified as local scale and movements >30.00 km were classified as relocation scale. Habitat selection at the local scale was generally influenced by local and landscape-level variables across all seasons. Variables in top models at the local scale included proximities to cropland, emergent wetland, open water, and woody wetland. Similarly, variables associated with area of cropland, emergent wetland, open water, and woody wetland were also included at the local scale. At the relocation scale, mallards selected resource units based on more generalized variables, including proximity to wetlands and total wetland area. Our results emphasize the role of landscape composition in waterbird habitat selection and provide further support for local wetland landscapes to be considered functional units of waterbird conservation and management.     

Influence of landscape structure on reef fish assemblages

Management of tropical marine environments calls for interdisciplinary studies and innovative methodologies that consider processes occurring over broad spatial scales. We investigated relationships between landscape structure and reef fish assemblage structure in the US Virgin Islands. Measures of landscape structure were transformed into a reduced set of composite indices using principal component analyses (PCA) to synthesize data on the spatial patterning of the landscape structure of the study reefs. However, composite indices (e.g., habitat diversity) were not particularly informative for predicting reef fish assemblage structure. Rather, relationships were interpreted more easily when functional groups of fishes were related to individual habitat features. In particular, multiple reef fish parameters were strongly associated with reef context. Fishes responded to benthic habitat structure at multiple spatial scales, with various groups of fishes each correlated to a unique suite of variables. Accordingly, future experiments should be designed to test functional relationships based on the ecology of the organisms of interest. Our study demonstrates that landscape-scale habitat features influence reef fish communities, illustrating promise in applying a landscape ecology approach to better understand factors that structure coral reef ecosystems. Furthermore, our findings may prove useful in design of spatially-based conservation approaches such as marine protected areas (MPAs), because landscape-scale metrics may serve as proxies for areas with high species diversity and abundance within the coral reef landscape.     

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.     

Influence of landscape structure on reef fish assemblages

Management of tropical marine environments calls for interdisciplinary studies and innovative methodologies that consider processes occurring over broad spatial scales. We investigated relationships between landscape structure and reef fish assemblage structure in the US Virgin Islands. Measures of landscape structure were transformed into a reduced set of composite indices using principal component analyses (PCA) to synthesize data on the spatial patterning of the landscape structure of the study reefs. However, composite indices (e.g., habitat diversity) were not particularly informative for predicting reef fish assemblage structure. Rather, relationships were interpreted more easily when functional groups of fishes were related to individual habitat features. In particular, multiple reef fish parameters were strongly associated with reef context. Fishes responded to benthic habitat structure at multiple spatial scales, with various groups of fishes each correlated to a unique suite of variables. Accordingly, future experiments should be designed to test functional relationships based on the ecology of the organisms of interest. Our study demonstrates that landscape-scale habitat features influence reef fish communities, illustrating promise in applying a landscape ecology approach to better understand factors that structure coral reef ecosystems. Furthermore, our findings may prove useful in design of spatially-based conservation approaches such as marine protected areas (MPAs), because landscape-scale metrics may serve as proxies for areas with high species diversity and abundance within the coral reef landscape.

     

Relating tradable credits for biodiversity to sustainability criteria in a dynamic landscape

Tradable biodiversity credit systems provide flexible means to resolve conflicts between development and conservation land-use options for habitats occupied by threatened or endangered species. We describe an approach to incorporate the influence of habitat fragmentation into the conservation value of tradable credits. Habitat fragmentation decreases gene flow, increases rates of genetic drift and inbreeding, and increases probabilities of patch extinction. Importantly, tradable credit systems will change the level of fragmentation over time for small and/or declining populations. We apply landscape equivalency analysis (LEA), a generalizable, landscape-scale accounting system that assigns conservation value to habitat patches based on patch contributions to abundance and genetic variance at landscape scales. By evaluating habitat trades using two models that vary the relationship between dispersal behaviors and landscape patterns, we show that LEA provides a novel method for limiting access to habitat at the landscape-scale, recognizing that the appropriate amount of migration needed to supplement patch recruitment and to offset drift and inbreeding will vary as landscape pattern changes over time. We also found that decisions based on probabilities of persistence alone would ignore changes in migration, genetic drift, and patch extinction that result from habitat trades. The general principle of LEA is that habitat patches traded should make at least equivalent contributions to rates of recruitment and migration estimated at a landscape scale. Traditional approaches for assessing the “take” and “jeopardy” standards under the Endangered Species Act based on changes in abundance and probability of persistence may be inadequate to prevent trades that increase fragmentation.