Habitat In Fragmented Landscapes Research Articles

Functional landscape connectivity for a select few: Linkages do not consistently predict wildlife movement or occupancy

Landscape-level connectivity models developed in geographic information systems (GIS) produce hypothetical objects proposed to connect areas of habitat in fragmented landscapes, hereafter called “linkages”. Assuming they are used by organisms in nature, linkages could be an important tool for the maintenance of viable wildlife populations and biodiversity conservation. We evaluated five California linkage models (four statewide and one desert specific) for use by common California mammal, reptile and amphibian species in two ways using >180,000 wildlife detections over 20 years. If species are using linkages more often than surrounding areas, we expect to find evidence of their occurrence within linkages significantly more than outside linkages. First, we focused on wildlife-vehicle collision (WVC) data as a proxy for wildlife movement across landscapes and tested whether linkages were an important predictor for the presence of WVCs. Second, we used occupancy modeling with inferred non-detections to assess whether linkages were important predictors of species presence on the landscape. We found that the linkage areas were not consistent predictors of WVCs, with the exception of certain large-bodied mammals by individual models. Linkage areas were also not important predictors for the probability of landscape occupancy for most species. These results show that, lacking validation, hypothetical landscape linkages alone will not support functional connectivity for general biodiversity conservation. Therefore, caution should be exercised when using linkages in land and transportation-based conservation planning. In urban environments, modeled linkages may reflect the critical last places for wildlife to move and should be reserved. However, in mixed-use landscapes where wildlife may move more easily, connectivity as a gradient across the landscape should be the target of conservation, including in land-use and transportation planning.

Flying through the forest canopy: Movement patterns and habitat selection of rescued and wild Harpy Eagles in the Brazilian Amazon

We tracked six Harpy Eagles (Harpia harpyja) by satellite telemetry from 2011 to 2021 in the Brazilian Amazonia, analyzing the used area, movements parameters and habitat selection functions for three of them: one adult within its breeding site, one translocated adult, and a four-years old floating subadult. We used the first-passage time to assess the scale at which these individuals respond to the environment, and the behavioral change point analysis to determine behavioral states parameters across trajectories. We fitted a logistic linear regression model with used-available locations and environmental covariates: slope, Terrain Ruggedness Index (TRI), Normalized Difference Vegetation Index (NDVI), land cover, and habitat edge as predictor variables. Harpy Eagle locations were highly related with “Forest” land cover and high NDVI values. The subadult and the translocated adult selected for “Secondary Forest” within their home ranges, which highlights the importance of this type of habitat in fragmented landscapes. In addition, we found behavioural differences in the movement paths of rehabilitated individuals of Harpy Eagle that are subsequently released to the wild. In conclusion, we suggest including in conservation management not only the nest tree and its immediately surrounding but also an area over landscape scale to optimize and promote the functional connectivity, with a safe and efficient dispersion of immatures. Linking Harpy Eagle´s movement locations to resources (land cover, NDVI), risks (forested habitat edge) and environmental conditions (slope, terrain ruggedness) is an opportunity to learn about habitat selection by this large canopy predator. The Harpy Eagle movement ecology has a potential relationship with the spatial dynamics of prey in the forest canopy, which needs to be further addressed in future research.

The decision-making process of leafcutting bees when selecting patches.

Change in land configuration is an important driver of pollinator decline. Understanding patch selection by bees in fragmented landscapes has therefore become imperative to guide the design of habitats that support pollinators and ensure their conservation. This is especially true for solitary bees that make up most bee species in the world. To elucidate the decision-making process of a solitary bee when selecting patches, we tested four models of patch attractiveness that differed in the role of patch size and isolation distance in the selection process. In these models, bees used both patch size and patch distance, only patch distance, or chose randomly among patches. When patch size was included, bees could estimate patch resources fully or partially. An experiment with a centre patch, surrounded by four peripheral patches of different sizes and distances from the centre, provided observed transition data to test against predictions derived from each of the models. The alfalfa leafcutting bee, Megachile rotundata, does not move randomly among patches. This bee uses both patch size and isolation distance when selecting a patch but can only evaluate patch resources partially. This knowledge can guide the design of habitats in fragmented landscapes to facilitate solitary bee conservation.

Dung beetles maintain phylogenetic divergence but functional convergence across a highly fragmented tropical landscape

Abstract Understanding how human‐modified landscapes affect the phylogenetic composition and assembly mechanisms of biological communities is critical for effectively managing and restoring tropical ecosystems. We evaluated how forest coverage loss, fragmentation and landscape heterogeneity affect the phylogenetic diversity of dung beetles and their assembly mechanisms in Los Tuxtlas Biosphere Reserve, a protected but highly fragmented tropical landscape. We calculated Faith's phylogenetic diversity, mean pairwise phylogenetic distance and mean nearest taxon distance for 5,388 individuals in 36 species. The standardised effect sizes of these metrics were estimated to control their correlation with species richness. Phylogenetic diversity was also assessed separately for each dung beetle functional group. Finally, we compared the mean functional and phylogenetic pairwise distance and mean nearest taxon distance and measured the phylogenetic signal among dung beetle functional traits to determine the influence of niche conservatism on the phylogenetic structure of species assemblages. Faith's phylogenetic diversity of dung beetles was positively correlated with forest coverage, while their mean phylogenetic and nearest taxon distance values decreased with increasing landscape fragmentation. Necrophagous beetles and forest specialists responded most negatively to forest coverage loss and fragmentation. Alpha and beta diversity values showed phylogenetic overdispersion but functional convergence and weak phylogenetic signals in their functional traits, suggesting low niche conservatism. Landscapes with moderate forest coverage (≥40%) favoured higher phylogenetic beta diversity, whereas phylogenetic and functional beta diversity decreased significantly in landscapes with low forest coverage (<30%). Synthesis and applications. Forest habitats in fragmented landscapes are essential for safeguarding the evolutionary history of dung beetles, reducing biotic homogenisation processes by favouring phylogenetic overdispersion and complementarity between sites. Therefore, to secure the phylogenetic diversity of dung beetles within fragmented tropical reserves, we recommend protecting the existing forests, preventing further fragmentation of continuous forest areas and increasing matrix quality by implementing biodiversity‐friendly production systems. Finally, managers should consider assessing different functional groups in other species, as their response to landscape disturbance may not be phylogenetically similar. The above will allow more effective management practices to protect the species most susceptible to disturbances.

Is There an Equivalence between Measures of Landscape Structural and Functional Connectivity for Plants in Conservation Assessments of the Cerrado?

Landscape connectivity can be assessed based on the physical connection (structural connectivity) or the maintenance of flow among habitats depending on the species (functional connectivity). The lack of empirical data on the dispersal capacity of species can lead to the use of simple structural measures. Comparisons between these approaches can improve decision-making processes for the conservation or restoration of habitats in fragmented landscapes, such as the Cerrado biome. This study aimed to understand the correspondence between the measures of landscape structural and functional connectivity for Cerrado plants. Three landscapes with cerradão patches in a pasture matrix were selected for the application of these metrics based on the functional connectivity of four profiles of plant dispersal capacity. The results showed divergent interpretations between the measures of landscape structural and functional connectivity, indicating that the assessment of biodiversity conservation and landscape connectivity is dependent on the set of metrics chosen. Structurally, the studied landscapes had the same number of cerradão patches but varied in optimal resource availability, isolation, heterogeneity, and aggregation. Functional connectivity was low for all profiles (based on the integral index of connectivity—IIC) and null for species with a low dispersal capacity (based on the connectance index—CONNECT), indicating that species with a medium- to long-distance dispersal capacity may be less affected by the history of losses and fragmentation of the Cerrado in the pasture matrix. The functional connectivity metrics used allowed a more robust analysis and, apparently, better reflected reality, but the lack of empirical data on dispersal capacity and the difficulty in choosing an indicator organism can limit their use in the management and planning of conservation and restoration areas.

Watershed influences on the structure and function of riparian wetlands associated with headwater streams – Kenai Peninsula, Alaska

Riparian wetlands are dynamic components of landscapes. Located between uplands and aquatic environments, riparian habitats intercept sediments and nutrients before they enter aquatic environments. They are a source of organic matter and nutrients to aquatic systems, and they provide important habitat for animals, often serving as corridors for the movement of animals between habitats in fragmented landscapes. In this project, we focused on the structure and function of riparian wetlands associated with headwater streams in Alaska that serve as nursery habitats for juvenile salmonids. We asked whether or not the structure and function of headwater wetlands differed between watersheds with and without nitrogen-fixing Alder (Alnus spp.). We found that the aboveground biomass of riparian vegetation was higher in the watershed with Alder, but the largest differences were in the litter layer and belowground where vegetation in the watershed with no Alder had significantly higher root biomass. Interstitial water chemistry also differed between the study sites with significantly higher inorganic N and significantly different characteristics of colored dissolved organic matter at the site with Alder on the watershed. The biomass of litter that hung over the creek bank was less at the site with Alder on the watershed and an in situ decomposition experiment showed significant differences between the two systems. Results of the research demonstrates that watershed characteristics can impact the ecology of headwater streams in ways that had not been previously recognized.

Response of a small felid of conservation concern to habitat fragmentation

Habitat loss and fragmentation are major drivers of biodiversity loss. A key question, particularly relevant to carnivore conservation, is to which extent species are able to survive in human-modified landscapes. Currently, conservationists are concerned about the impact habitat fragmentation may have on the long-term persistence of the forest-dwelling guina (Leopardus guigna), given the increasingly modified landscapes in which they live. Here we evaluate the effect habitat cover, fragmentation and anthropogenic pressure have on the occupancy probability for guinas in privately-owned forest fragments. We collected camera-trap data from 100 temperate rainforest sites in Chile and used single-season occupancy modeling to evaluate the influence of 13 parameters of landscape structure/anthropogenic pressure and four parameters of detection probability on the ocurrence of guinas. The camera-trap survey data comprised 4168 camera-trap days and 112 independent records of guinas. Surprisingly, fragmented (defined as having a high perimeter-to-area ratio) and moderately sized habitat patches best predicted site occupancy. Occupancy also increased where habitat patches were closer to continuous forest and nearer to buildings. Our results imply that guinas can benefit from a high degree of edge type habitats in fragmented landscapes, capable of adapting to habitat fragmentation in the proximity to large continuous forest patches. This suggests that guinas have a broader niche than previously believed. Additionally, the guina is tolerant of human infrastructure. Further research is required to identify potential ecological traps, long-term source-sink dynamics, and the habitat loss/fragmentation threshold beyond which guina populations are no longer viable.

The extent of edge effects in fragmented landscapes: Insights from satellite measurements of tree cover

Due to deforestation, intact tropical forest areas are increasingly transformed into a mixture of remaining forest patches and human modified areas. These forest fragments suffer from edge effects, which cause changes in ecological and ecosystem processes, undermining habitat quality and the offer of ecosystem services. Even though detailed and long term studies were developed on the topic of edge effects at local scale, understanding edge effect characteristics in fragmented forests on larger scales and finding indicators for its impact is crucial for predicting habitat loss and developing management options. Here we evaluate the spatial and temporal dimensions of edge effects in large areas using remote sensing. First we executed a neighborhood pixel analysis in 11 LANDSAT Tree Cover (LTC) scenes (180×185km each, 8 in the tropics and 3 in temperate forested areas) using tree cover as an indicator of habitat quality and in relation to edge distance. Second, we executed a temporal analysis of LTC in a smaller area in the Brazilian Amazon forest where one larger forest fragment (25,890ha) became completely fragmented in 5years. Our results show that for all 11 scenes pixel neighborhood variation of LTC is much higher in the vicinity of forest edges, becoming lower towards the forest interior. This analysis suggests a maximum distance for edge effects and can indicate the location of unaffected core areas. However, LTC patterns in relation to fragment edge distance vary according to the analyzed region, and maximum edge distance may differ according to local conditions. Our temporal analysis illustrates the change in tree cover patterns after 5years of fragmentation, becoming on average lower close to the edge (between 50 and 100m). Although it is still unclear which are the main causes of LTC edge variability within and between regions, LANDSAT Tree Cover could be used as an accessible and efficient discriminator of edge and interior forest habitats in fragmented landscapes, and become invaluable for deriving qualitative spatial and temporal information of ecological and ecosystem processes.

Rapid genetic restoration of a keystone species exhibiting delayed demographic response.

Genetic founder effects are often expected when animals colonize restored habitat in fragmented landscapes, but empirical data on genetic responses to restoration are limited. We examined the genetic response of banner-tailed kangaroo rats (Dipodomys spectabilis) to landscape-scale grassland restoration in the Chihuahuan Desert of New Mexico, USA. Dipodomys spectabilis is a grassland specialist and keystone species. At sites treated with herbicide to remove shrubs, colonization by D. spectabilis is slow and populations persist at low density for ≥10 years (≥6 generations). Persistence at low density and low gene flow may cause strong founder effects. We compared genetic structure of D. spectabilis populations between treated sites and remnant grasslands, and we examined how the genetic response to restoration depended on treatment age, area, and connectivity to source populations. Allelic richness and heterozygosity were similar between treated sites and remnant grasslands. Allelic richness at treated sites was greatest early in the restoration trajectory, and genetic divergence did not differ between recently colonized and established populations. These results indicated that founder effects during colonization of treated sites were weak or absent. Moreover, our results suggested founder effects were not mitigated by treatment area or connectivity. Dispersal is negatively density-dependent in D. spectabilis, and we hypothesize that high gene flow may occur early in the restoration trajectory when density is low. Our study shows genetic diversity can be recovered more rapidly than demographic components of populations after habitat restoration and that founder effects are not inevitable for animals colonizing restored habitat in fragmented landscapes.

Melding kin structure and demography to elucidate source and sink habitats in fragmented landscapes

The source‐sink model undoubtedly is one of the most established paradigms for associating variance in population dynamics with heterogeneity in habitat quality. However, despite extensive theoretical support by the scientific community, the majority of studies seeking empirical validation for this model have lacked sufficient data to distinguish source and sink habitats, particularly for large or secretive mammals. Using relatively long‐term mark‐recapture and genetic data for a generalist mesopredator within a fragmented agricultural ecosystem, we show that use of a two‐stage approach incorporating both genetic and demographic data can be a powerful tool for evaluating the population structure of organisms occupying complex ecological systems. We further demonstrate that a strong concordance exists between demographic attributes and underlying genetic expectations, suggesting evaluation of fine‐scale genetic patterns alone may provide valuable insights into the population dynamics of species. These data have important implications for advancing our ability to quantify heterogeneity in population stability, particularly for large or imperiled species where sufficient demographic data cannot be obtained to parameterize traditional source‐sink models.

Can vegetation corridors provide habitat in fragmented landscapes? A case-study in the Brazilian Atlantic Domain

This is the first study evaluating the vegetation corridor as habitat in Brazilian Atlantic Forest. We used the marsupial Marmosops incanus, a forest specialist, as a model. Our main question was: does the vegetation corridor provide habitat for populations of this species? We found that the corridor harbored males and females in the same proportion and equally distributed by age classes. Body weights of males and females captured in the corridor did not differ from those of individuals in the forest fragments. Our results showed that the corridor acts as a suitable habitat for M. incanus. Thus, this study highlights the importance of conserving vegetation corridors.

Within-territory use of different land cover types by tropical forest birds in a fragmented landscape

Many terrestrial species of birds have been observed to depend on large contiguous areas of forest; in the tropics this appears to be especially true for terrestrial insectivores. Far less is understood about how more-common species, that are less dependent on interior forests, use both forested and non-forested habitat in fragmented landscapes. Using both behavioral observations and radio-tracking relocation data, I quantified the within-territory use of different land cover types for three tropical songbird species, the dusky antbird (Cercomacra tyrannina), red-throated ant-tanager (Habia fuscicauda), and cocoa woodcreeper (Xiphorhynchus susurrans). Small forest fragments (<50ha) were also surveyed for these same species. Territories of all three species were mostly forest (>75%), with different amounts of non-forested land cover. As predicted, all three species had increased use in forest cover and decreased use where neighboring territories overlapped. In addition all three species had higher use of areas where there were more forest gaps and/or ‘soft edges’ in the vicinity. Dusky antbirds were less likely to use monocultures of non-native grass and impervious surfaces, while the other two species had mixed responses to non-forested habitats. Dusky antbirds and cocoa woodcreepers were observed foraging at higher-than-expected frequencies along ‘hard edges’ of forested habitat. All three species were found in forest fragments even smaller than a minimal home range area estimate. Conservation of more-common bird species in fragmented landscapes can include secondary forests and small remnants but for these three species non-forested land cover alone would not be expected to provide breeding habitat.

Dispersing Siberian flying squirrels (Pteromys volans) locate preferred habitats in fragmented landscapes

In fragmented landscapes, dispersal abilities determine the potential of a species to colonize temporally unoccupied habitats. For example in territorial species, even the high-quality sites will be temporally unoccupied between the death of residents and recolonization by dispersers. This has implications for conservation management, because whether or not unoccupied habitats are worthy of protecting depends on likelihood that these sites will be recolonized in the near future. We analysed the ability of dispersing Siberian flying squirrels ( Pteromys volans (L., 1758)) to locate the preferred habitats. Dispersers encountered many patches of preferred habitat and, in the end, a majority of them successfully settled in these patches. The dispersal distance increased with increasing distance between patches, but settlement in preferred patches and short-term mortality were independent of dispersal distance or distance between available patches. We conclude that dispersers were effective in locating the preferred habitat in fragmented landscapes. Indeed, large interpatch distances partly explain that dispersal distances are longer in flying squirrels than usually observed in similar-sized mammals. For conservation management, our findings encourage managers to protect temporally unoccupied, high-quality habitats in addition to occupied habitats to promote a sustainable habitat network in space and time.

Frugivory, Post-feeding Flights of Frugivorous Birds and the Movement of Seeds in a Brazilian Fragmented Landscape

Habitat fragmentation can break down the movement processes of frugivorous animals, thus influencing the relationship between plants and their seed dispersers by altering the number and identity of seed dispersers, and their relative contribution to seed dispersal. We studied the assemblages of frugivorous birds, their composition, species richness, and visitation rates to fruiting plants growing in the different landscape elements (forest fragments, live fences, and trees isolated in pastures) embedded in a Brazilian fragmented, agricultural landscape. By following the post-feeding movements of frugivorous birds, we inferred the direction of seed movement from and to each of these landscape elements. Fruiting trees growing at different landscape elements were visited by frugivorous birds at similar rates. Isolated trees attracted a greater and distinct bird assemblage than trees in forest fragments or live fences. Judging by the post-feeding flights of birds, the seeds of isolated trees were the most likely to reach all the landscape elements considered, but the contribution of isolated trees to the seeds falling in forested habitats or pastures depended on their degree of isolation. A few bird species were able to move widely, visiting fruiting plants in all landscape elements, and promoting long-distance dispersal for plants. These few birds are of special interest because they are mobile links that connect habitats in fragmented landscapes with their seed dispersal services.

Effects of Restoring Oak Savannas on Bird Communities and Populations

Efforts to restore and maintain oak savannas in North America, with emphasis on the use of prescribed fire, have become common. Little is known, however about how restoration affects animal populations, especially those of birds. I compared the breeding densities, community structure, and reproductive success of birds in oak savannas maintained by prescribed fire (12 sites) with those in closed-canopy forests (13 sites). All sampling was conducted in Illinois (U.S.A.). Of the 31 bird species analyzed, 12 were more common in savannas, 14 were not affected by habitat structure, and 5 were more common in forest habitat. The species favored by disturbance and restoration included Northern Bobwhites (Colinus virginianus), Mourning Doves (Zenaida macroura), Red-headed Woodpeckers (Melanerpes erythrocephalus), Indigo Buntings (Passerina cyanea), and Baltimore Orioles (Icterus galbula). Those more common in closed-canopy forest included Ovenbirds (Seiurus aurocapilla) and Wood Thrushes (Hylocichla mustelina). Few species were unique to one type of habitat, but overall avian community structure in oak savannas and closed-canopy forests was generally distinctive. Estimates of nesting success (derived from 785 nests) revealed that 6 of the 13 species considered experienced greater productivity in the savanna habitat. Rates of brood parasitism were unaffected by restoration and habitat structure. Within savannas, tract size had little effect on breeding abundances and reproductive success. My results illustrate that restoration techniques can significantly affect the ecology of constituent animal populations and communities and have key implications regarding avian conservation and the management of forest habitat in fragmented landscapes. Small patches of forest habitat that regularly function as population sinks may offer far better prospects for birds if they are subjected to disturbance and ecosystem restoration.

Predicting which species will benefit from corridors in fragmented landscapes from population growth models.

Connecting isolated patches of habitat in fragmented landscapes with corridors is a popular conservation strategy. This strategy is also controversial in large part because of uncertainty about what characteristics of a species and its environment promote corridor use. In this article we address the question, For what types of species will populations benefit from corridors? We asked this question using a model of two logistically growing populations connected by migration in which both emigration and migration success were determined by the presence or absence of a corridor. We found that in the short run (e.g., during recovery from disaster), corridors are most effective for species with fast-growing populations that have low survivorship when dispersing through unsuitable (matrix) habitat. We also found that emigration rates and habitat-specific mortality rates are key determinants of the effects of corridors on population size. In the long term, corridors are most likely to benefit species with slow-growing populations that have low survivorship when dispersing through matrix habitat. Our results confirm the major conclusions from previous empirical studies of corridor benefits. However, most studies fail to consider the most appropriate questions to determine the potential benefits of habitat corridors. First, what is the time scale of the conservation goal? Corridors have positive effects on different suites of species in the short and long term. Second, is the major threat of local extinction due to sustained population decline or boom-bust cycles? Third, what is the migration rate through the matrix? Fourth, what fraction of migrants dispersing through the matrix successfully immigrate to another patch?

Dispersal and extinction in fragmented landscapes.

Evolutionary and population dynamics models suggest that the migration rate will affect the probability of survival in fragmented landscapes. Using data for butterfly species in the fragmented British landscape and in immediately adjoining areas of the European continent, this paper shows that species of intermediate mobility have declined most, followed by those of low mobility, whereas high-mobility species are generally surviving well. Compared to the more sedentary species, species of intermediate mobility require relatively large areas where they breed at slightly lower local densities. Intermediate mobility species have probably fared badly through a combination of metapopulation (extinction and colonization) dynamics and the mortality of migrating individuals which fail to find new habitats in fragmented landscapes. Habitat fragmentation is likely to result in the non-random extinction of populations and species characterized by different levels of dispersal, although the details are likely to depend on the taxa, habitats and regions considered.

Distributions of occupied and vacant butterfly habitats in fragmented landscapes: C. D. Thomas, J. A. Thomas & M. S. Warren, Oecologia, 92(4), 1992, pp 563–567

Distributions of occupied and vacant butterfly habitats in fragmented landscapes: C. D. Thomas, J. A. Thomas & M. S. Warren, Oecologia, 92(4), 1992, pp 563–567

Distributions of occupied and vacant butterfly habitats in fragmented landscapes

We found several rare UK butterflies to be restricted to relatively large and non-isolated habitat patches, while small patches and those that are isolated from population sources remain vacant. These patterns of occurrence are generated by the dynamic processes of local extinction and colonization. Habitat patches act as terrestrial archipelagos in which long-term population persistence, and hence effective long-term conservation, rely on networks of suitable habitats, sufficiently close to allow natural dispersal.