Effect of Landscape Structure on Species Diversity

The effects of habitat fragmentation and their implications for biodiversity is a central issue in conservation biology which still lacks an overall comprehension. There is not yet a clear consensus on how to quantify fragmentation even though it is quite common to couple the effects of habitat loss with habitat fragmentation on biodiversity. Here we address the spatial patterns of species distribution in fragmented landscapes, assuming a neutral community model. To build up the fragmented landscapes, we employ the fractional Brownian motion approach, which in turn permits us to tune the amount of habitat loss and degree of clumping of the landscape independently. The coupling between the neutral community model, here simulated by means of the coalescent method, and fractal neutral landscape models enables us to address how the species–area relationship changes as the spatial patterns of a landscape is varied. The species–area relationship is one of the most fundamental laws in ecology, considered as a central tool in conservation biology, and is used to predict species loss following habitat disturbances. Our simulation results indicate that the level of clumping has a major role in shaping the species–area relationship. For instance, more compact landscapes are more sensitive to the effects of habitat loss and speciation rate. Besides, the level of clumping determines the existence and extension of the power-law regime which is expected to hold at intermediate scales. The distributions of species abundance are strongly influenced by the degree of fragmentation. We also show that the first and second commonest species have approximately self-similar spatial distributions across scales, with the fractal dimensions of the support of the first and second commonest species being very robust to changes in the spatial patterns of the landscape.     

Ecological traits and landscape characteristics predicting bird sensitivity to urbanization in city parks

Habitat loss and fragmentation caused by urbanization often have negative impacts on wildlife in cities. There are considerable studies investigating the relationship between species traits and fragmentation vulnerability. However, so far, very few studies have examined the influence of species traits combined with landscape factors on vulnerability to urbanization in urbanized landscapes. In this study, we investigated how species traits and park characteristics influenced bird sensitivity to urbanization in the highly urbanized city of Nanjing, China. We used the line-transect method to survey birds in 37 urban parks. For each bird species, we collected data on nine life-history and ecological traits that are commonly assumed to influence urbanization vulnerability. For each park, we selected six landscape variables that are commonly considered to influence bird response to urbanization. After phylogenetic correction, the nine species traits were used separately and in combination to evaluate their associations with species abundance, an indicator of urbanization vulnerability. We then used the RLQ and fourth-corner analyses to test relationships between species traits and environmental variables. We found that the 75 species analyzed demonstrated considerable variation in vulnerability to urbanization. Using PGLS analyses and model averaging, we found that habitat specificity was the single best ecological predictor of urbanization vulnerability in birds in Nanjing city parks. The RLQ analysis showed that body size and habitat specificity were correlated with distance to city center and connectivity of the parks, reflecting strong effects of trait-mediated environmental filters that selectively benefit species with smaller body mass and lower habitat specificity in urbanized landscape. Therefore, conservation efforts giving priority to species with high habitat specificity and to parks with high connectivity and far away from the city center may prove effective for the preservation of bird diversity in our highly urbanized system. Meanwhile, preventing future habitat loss and destruction in existing city parks may also effectively conserve these vulnerable species.     

区域城市扩张对森林景观破碎化的影响——以粤港澳大湾区为例

森林生境丧失与景观破碎化是引起生物多样性下降,生态系统功能降低的重要原因。量化森林景观破碎化的时空特征及其与城市扩张格局的关系是开展区域生态修复与功能提升的重要基础。本文以快速城市化的典型区域——粤港澳大湾区为研究对象,基于遥感解译的1980年、1990年、2000年、2010年和2018年土地覆盖/利用专题图,通过多尺度的景观格局分析和统计分析,定量解析森林景观破碎化的时空演变特征及其与城市扩张格局间的关系。研究结果显示：1）1980-2018年,大湾区林地覆盖面积缩减1,274 km²,林地转变为建设用地的面积占林地丧失总面积的比例从1980-1990年的11%增长至2010-2018年的42%,表明城市扩张已成为林地丧失的主导因素;2）森林景观破碎化程度加剧,表现为林地斑块密度提高,平均斑块面积减小,但破碎类型与程度具有地域差异;3）城市扩张幅度与空间格局显著影响林地破碎化,其中,城市扩张幅度对林地破碎化的影响更为重要。基于森林景观破碎化与城市扩张的现状,落实城市增长边界划定、关键斑块-廊道识别与生态网络构建等措施,有助于保护与连通重要生态空间,保障和提升生态功能。     

Bird community responses to habitat fragmentation: how consistent are they across landscapes?

Aim The woodland ecosystems of south‐eastern Australia have been extensively disturbed by agriculture and urbanization. Herein, the occurrence of birds in woodland remnants in three distinct landscapes was analysed to examine the effects of different types of landscape matrices on species richness vs. area and species richness vs. isolation relationships and individual species responses to woodland fragmentation. Location The study system comprised three distinct woodland landscapes of the northern Australian Capital Territory and bordering areas of New South Wales. These landscapes (termed agricultural, peri‐urban and urban) are located within 50 km of each other, have remnant fragments of similar age, size, isolation, woodland cover, elevation and climates. The major distinguishing feature of the three landscapes was the properties of the habitats surrounding the numerous woodland remnants. Methods Bird surveys, using an area‐search methodology, were conducted in 1999 and 2000 in 127 remnants in the three landscapes to determine bird species presence/absence. Each remnant was characterized by measures of remnant area, isolation and habitat complexity. To characterize differences between each landscape, we conducted an analysis of the amount of tree cover and human disturbance in each landscape using SPOT imagery and aerial photographs. Linear regressions of woodland‐dependent species richness vs. remnant area and remnant isolation for the three different landscapes were calculated to see if there were any apparent differences. Binomial logistic regressions were used to determine the relationships between the occurrence of each species and the size and isolation of woodland habitat, in each landscape. Results All the landscapes displayed a significant (P < 0.01) species vs. area relationship, but the slope of the urban relationship was significantly greater than those of the other landscapes. In contrast, only the agricultural landscape displayed a significant (P < 0.01) species richness vs. isolation relationship. When individual species were investigated, we found species that were: (1) apparently insensitive to reduction in remnant area and increase in isolation across all landscapes, (2) absent in small remnants in all landscapes, (3) absent in small remnants in all landscapes and also absent in isolated remnants in the agricultural landscape, (4) absent in isolated remnants in the agricultural landscape, and (5) absent in small remnants in the urban landscape. Threshold values (50% probability of occurrence) for area and isolation for individual species were highly variable across the three landscapes. Main conclusions These results indicate that woodland bird communities have a varying response to habitat fragmentation in different landscapes. Whilst we cannot be sure how representative our chosen landscapes are of other similarly composed landscapes, these results suggest that the type of landscape matrix may have a considerable influence on how bird species are affected by woodland fragmentation in the region. For instance, the properties of a matrix may influence both the resources available in the landscape as a whole for different bird species, and the connectivity (dispersal of birds), between woodland remnants. We encourage further research that examines these hypotheses and argue that the management of the matrix should be included in conservation strategies for fragmented landscapes.     

The Effects of Landscape Variables on the Species-Area Relationship during Late-Stage Habitat Fragmentation

Few studies have focused explicitly on the later stages of the fragmentation process, or "late-stage fragmentation", during which habitat area and patch number decrease simultaneously. This lack of attention is despite the fact that many of the anthropogenically fragmented habitats around the world are, or soon will be, in late-stage fragmentation. Understanding the ecological processes and patterns that occur in late-stage fragmentation is critical to protect the species richness in these fragments. We investigated plant species composition on 152 islands in the Thousand Island Lake, China. A random sampling method was used to create simulated fragmented landscapes with different total habitat areas and numbers of patches mimicking the process of late-stage fragmentation. The response of the landscape-scale species-area relationship (LSAR) to fragmentation per se was investigated, and the contribution of inter-specific differences in the responses to late-stage fragmentation was tested. We found that the loss of species at small areas was compensated for by the effects of fragmentation per se, i.e., there were weak area effects on species richness in landscapes due to many patches with irregular shapes and high variation in size. The study also illustrated the importance of inter-specific differences for responses to fragmentation in that the LSARs of rare and common species were differently influenced by the effects of fragmentation per se. In conclusion, our analyses at the landscape scale demonstrate the significant influences of fragmentation per se on area effects and the importance of inter-specific differences for responses to fragmentation in late-stage fragmentation. These findings add to our understanding of the effects of habitat fragmentation on species diversity.     

A transient,positive effect of habitat fragmentation on insect population densities

We conducted an experimental landscape study to test the hypotheses that: (1) habitat removal results in short-term increases in population density in the remaining habitat patches (the crowding effect); (2) following habitat removal, density is higher in landscapes with more, smaller patches and more habitat edge (i.e., a higher level of habitat fragmentation per se) than in less fragmented landscapes, for the same total amount of habitat on the landscapes; (3) this positive effect of fragmentation per se on density is larger in landscapes with smaller inter-patch distances; and (4) these last two effects should be reduced or disappear over time following habitat removal. Our results did not support the first hypothesis, but they provided some support for the other three hypotheses, for two of the four Coccinellid species studied. As in other empirical studies of fragmentation per se on population density, the effects of fragmentation per se were weak and positive (when they did occur). This is the first study to document a transient effect of fragmentation per se on population density, and to show that this effect depends on inter-patch distances. We suggest that fragmentation per se increased the rate of immigration to patches, resulting in higher population densities in more fragmented landscapes.     

Direct versus indirect effects of habitat fragmentation on community patterns in experimental landscapes

Habitat area and fragmentation are confounded in many ecological studies investigating fragmentation effects. We thus devised an innovative experiment founded on fractal neutral landscape models to disentangle the relative effects of habitat area and fragmentation on arthropod community patterns in red clover (Trifolium pratense). The conventional approach in experimental fragmentation studies is to adjust patch size and isolation to create different landscape patterns. We instead use fractal distributions to adjust the overall amount and fragmentation of habitat independently at the scale of the entire landscape, producing different patch properties. Although habitat area ultimately had a greater effect on arthropod abundance and diversity in this system, we found that fragmentation had a significant effect in clover landscapes with ≤40 % habitat. Landscapes at these lower habitat levels were dominated by edge cells, which had fewer arthropods and lower richness than interior cells. Fragmentation per se did not have a direct effect on local-scale diversity, however, as demonstrated by the lack of a broader landscape effect (in terms of total habitat area and fragmentation) on arthropods within habitat cells. Fragmentation—through the creation of edge habitat—thus had a strong indirect effect on morphospecies richness and abundance at the local scale. Although it has been suggested that fragmentation should be important at low habitat levels (≤20–30 %), we show that fragmentation per se is significant only at intermediate (40 %) levels of habitat, where edge effects were neither too great (as at lower levels of habitat) nor too weak (as at higher levels of habitat).     

Landscape-level comparison of genetic diversity and differentiation in a small mammal inhabiting different fragmented landscapes of the Brazilian Atlantic Forest

Habitat loss and fragmentation can have detrimental effects on all levels of biodiversity, including genetic variation. Most studies that investigate genetic effects of habitat loss and fragmentation focus on analysing genetic data from a single landscape. However, our understanding of habitat loss effects on landscape-wide patterns of biodiversity would benefit from studies that are based on quantitative comparisons among multiple study landscapes. Here, we use such a landscape-level study design to compare genetic variation in the forest-specialist marsupial Marmosops incanus from four 10,000-hectare Atlantic forest landscapes which differ in the amount of their remaining native forest cover (86, 49, 31, 11 %). Additionally, we used a model selection framework to evaluate the influence of patch characteristics on genetic variation within each landscape. We genotyped 529 individuals with 12 microsatellites to statistically compare estimates of genetic diversity and genetic differentiation in populations inhabiting different forest patches within the landscapes. Our study indicates that before the extinction of the specialist species (here in the 11 % landscape) genetic diversity is significantly reduced in the 31 % landscape, while genetic differentiation is significantly higher in the 49 and 31 % landscapes compared to the 86 % landscape. Results further provide evidence for non-proportional responses of genetic diversity and differentiation to increasing habitat loss, and suggest that local patch isolation impacts gene flow and genetic connectivity only in the 31 % landscape. These results have high relevance for analysing landscape genetic relationships and emphasize the importance of landscape-level study designs for understanding habitat loss effects on all levels of biodiversity.     

城市化背景下景观破碎化及连接度动态变化研究——以昆明市为例

城市化不仅改变景观类型和组成,也导致空间形态变化与自然生境连接度的降低,刻画不同城市化过程中人工表面、耕地与自然生境的空间关系对于研究其景观生态效应,尤其是对不同景观之间的相互作用以及结构和功能的变化具有重要意义。以云南省昆明市为研究区,分析了1990—2015年城市扩张导致的破碎化与形态变化对景观连接度的影响。利用城市破碎指数(UFI)刻画景观破碎水平,进一步基于形态学空间格局分析(MSPA)得到耕地和自然生境的七类景观形态要素(核心、岛状斑块、桥接、环岛、孔隙、边缘和支线),选取了3种边缘宽度比较边缘宽度对景观形态的影响差异,然后通过概率连接度指数(PC)和斑块重要值(dPC)评估景观连接度的变化。在4 km×4 km的网格基础上计算平均UFI和dPC,利用三维曲面分析不同变量之间的相关性。结果表明:过去25年间,昆明市人工表面不断扩大,占用大量耕地并导致景观破碎度的增加,速率呈逐年增加的趋势;MSPA结果显示,耕地表现出持续稳定的消减,自然生境景观形态类型前期变化不大,2010年后有较大幅度改变,表现出从稳定、波动到破碎的过程,不同边缘宽度下存在显著差别,边缘宽度越大则连接度变化越为明显,表明城市化对小型绿色斑块影响较大;斑块重要值与UFI的变化表现出一致性,变化集中于东部地区,随着UFI的增加景观连接度逐年降低;相关性分析显示,随着破碎度的增加,景观连接度经历了从波动到稳定下降的过程。总体上,昆明市城市化造成耕地的持续减少,虽未造成大面积自然生境丧失,但在一定程度上降低了连接度,需要从空间格局上加以管控,避免对整体景观连接度产生负面影响。     

城市化景观格局对本土植物多样性的多尺度影响——以北京市顺义区为例

景观格局对植物多样性的影响已经在很多研究中得到了验证,但有关城市景观的影响仍然知之甚少。为了探究城市化景观格局对植物多样性的影响及其尺度效应,本研究在北京市顺义区调查了105个样地,计算每个样地的α和β多样性指数;并以100 m为步长,分析了100～1000 m范围内的10个尺度43个城市的景观格局指数。结果表明: 在所有尺度上,城市景观面积指数、核心类指数和边缘指数与本土植物多样性均呈负相关;形状复杂性指数在小尺度内有利于植物多样性,而面积加权复杂性指数则在较大尺度上影响明显。其他指数如城市斑块的连接性、邻近性、内聚性、破碎性和散布并列指数与本土植物多样性之间的关系轻微且不稳定。城市化强度与尺度呈负相关,与各个尺度的植物多样性呈负相关。合理将城市区域分为许多边缘简单的小斑块,能够更好地保护本土植物多样性。该研究提出了保护城市植物多样性的景观格局建议,为生态城市建设提供参考。     

城市景观破碎化格局与城市化及社会经济发展水平的关系——以北京城区为例

快速城市化引发的景观破碎化加剧对于城市生态系统的过程、功能及其所提供的生态服务功能具有显著的影响。以北京市五环内中心城区为例,采用移动窗口分析、梯度分析与景观指数相结合的方法研究了城市景观破碎化的空间分布格局和内部水平差异,并以此为基础,探究景观破碎化与城市化及社会经济发展水平的关系。结果表明:类型水平上,城市建筑用地景观比例达63%,斑块连通性好,破碎化程度低,而绿地景观占33%,斑块分布不均匀,破碎化程度较高。景观水平上,城市中心和郊区的景观破碎化程度要明显低于城市边缘的城乡过渡区,沿城市化梯度从中心向外围呈现出先上升后下降的趋势。回归分析结果表明,景观破碎化程度与城市化水平之间表现出一种倒"U"型关系,并在城市化水平达42%—45%之间,景观破碎化程度达到峰值。进一步研究表明,人口密度和家庭户数是导致景观破碎化加剧的直接驱动因素,而经济的快速增长对景观破碎化程度的提高具有间接的影响。该研究结果不仅能作为城市生态系统监测的重要指标,还能为城市景观的合理规划提供科学依据,而且对于促进城市的可持续发展具有重要的意义。     

生境破碎化对动物种群存活的影响

生境破碎是生物多样性下降的主要原因之一。通常以岛屿生物地理学、异质种群生物学和景观生态学的理论来解释不同空间尺度中生境破碎化的生态学效应。生境破碎化引起面积效应、隔离效应和边缘效应。这些效应通过影响动物种群的绝灭阈值、分布和多度、种间关系以及生态系统过程,最终影响动物种群的存活。野外研究表明,破碎化对动物的影响,因物种、生境类型和地理区域不同而有所变化,因此,预测物种在破碎生境中的存活比较困难。研究热点集中于：确定生境面积损失和生境斑块的空间格局对破碎景观中物种绝灭的相对影响,破碎景观中物种的适宜生境比例和绝灭阈值,异质种群动态以及生态系统的生态过程。随着3S技术的发展,生境破碎化模型趋于复杂,而发展有效的模型和验证模型将成为一项富有挑战性的任务。     

Landscape size affects the relative importance of habitat amount,habitat fragmentation,and matrix quality on forest birds

It is important to understand the relative effects of landscape habitat loss, habitat fragmentation, and matrix quality on biodiversity, so that potential management options can be appropriately ranked. However, their effects and relative importance may change with the size of the landscape considered because the multiple (and potentially conflicting) ecological processes that are influenced by landscape structure occur at different spatial scales (e.g. dispersal, predation, foraging). We estimated the relative effects of habitat loss, habitat fragmentation, and matrix quality (measured as the amount of forest, the proportion of forest area contained in large core forests, and the density of roads respectively) on fragmentation‐sensitive forest birds in southern Ontario, Canada using a range of landscape sizes (0.8–310 km²). We used three complementary statistical approaches to estimate relative effects of these correlated landscape factors – 1) multiple regression, 2) information theoretic (AIC) estimates of the most parsimonious model, and 3) multi‐model inference to average effects across all supported models. We controlled for spatial autocorrelation, local habitat, roadside sampling bias, time of day, season, habitat heterogeneity, and the interaction between the effects of habitat amount and fragmentation. We found that relative effects of habitat amount and fragmentation were scale dependent; habitat amount had a consistently positive effect that was consistent over more than two orders of magnitude in landscape area (~1–300 km²). In contrast, the effects of habitat fragmentation depended on the size of the landscape considered. Indeed, for veery Catharus fuscescens, habitat fragmentation had positive effects at one scale and negative effects at another. The effects of matrix quality were generally weak and changed little with scale. For the number of fragmentation sensitive species and the presence of veery, habitat amount was most important in large landscapes and habitat fragmentation in small landscapes but for the presence of ovenbird Seiurus aurocapilla, habitat amount was most important at all scales.     

Habitat Loss,Not Fragmentation,Drives Occurrence Patterns of Canada Lynx at the Southern Range Periphery

Peripheral populations often experience more extreme environmental conditions than those in the centre of a species'' range. Such extreme conditions include habitat loss, defined as a reduction in the amount of suitable habitat, as well as habitat fragmentation, which involves the breaking apart of habitat independent of habitat loss. The ‘threshold hypothesis’ predicts that organisms will be more affected by habitat fragmentation when the amount of habitat on the landscape is scarce (i.e., less than 30%) than when habitat is abundant, implying that habitat fragmentation may compound habitat loss through changes in patch size and configuration. Alternatively, the ‘flexibility hypothesis’ predicts that individuals may respond to increased habitat disturbance by altering their selection patterns and thereby reducing sensitivity to habitat loss and fragmentation. While the range of Canada lynx (Lynx canadensis) has contracted during recent decades, the relative importance of habitat loss and habitat fragmentation on this phenomenon is poorly understood. We used a habitat suitability model for lynx to identify suitable land cover in Ontario, and contrasted occupancy patterns across landscapes differing in cover, to test the ‘threshold hypothesis’ and ‘flexibility hypothesis’. When suitable land cover was widely available, lynx avoided areas with less than 30% habitat and were unaffected by habitat fragmentation. However, on landscapes with minimal suitable land cover, lynx occurrence was not related to either habitat loss or habitat fragmentation, indicating support for the ‘flexibility hypothesis’. We conclude that lynx are broadly affected by habitat loss, and not specifically by habitat fragmentation, although occurrence patterns are flexible and dependent on landscape condition. We suggest that lynx may alter their habitat selection patterns depending on local conditions, thereby reducing their sensitivity to anthropogenically-driven habitat alteration.     

Assessing environmental requirements effects on forest fragmentation sensitivity in two arboreal rodents

The study of the effect of habitat fragmentation on species that inhabit residual patches requires the investigation of the relationship existing between species distribution and landscape components. To understand which components of landscape mosaics are more influential for species’ persistence, we compared the distribution of two arboreal rodents proved to be sensitive to habitat fragmentation, the hazel dormouse Muscardinus avellanarius and the red squirrel Sciurus vulgaris. Their occurrence in residual oak woods in central Italy was studied with nest-boxes and hair-tubes, developing a new method for hair analysis. Their distributions were analysed considering patch, matrix composition and configuration, and landscape vegetation variables. The two species showed a different degree of plasticity, with the squirrel being significantly more specialised at the landscape scale. The comparison of the two distribution patterns highlighted the influence of different ecological constraints and the existence of different strategies to cope with fragmentation. Patch size and patch attributes were generally weaker determinants of occurrence, compared to landscape metrics. The squirrel presence was significantly influenced by the presence of shared perimeter between hedgerows and woods and by the lack of isolation of the residual patches, suggesting the use of several fragments to compensate the low habitat quality. Conversely the hazel dormouse seemed to be more affected by the internal management of the woods, and in particular by the mean DBH. Our results highlight how the recognition of the extrinsic constraints and the influence of multi-scale habitat selection may help guiding land use management, to ensure species conservation in profoundly exploited landscapes.     

Characterising extinction debt following habitat fragmentation using neutral theory

Habitat loss leads to species extinctions, both immediately and over the long term as ‘extinction debt’ is repaid. The same quantity of habitat can be lost in different spatial patterns with varying habitat fragmentation. How this translates to species loss remains an open problem requiring an understanding of the interplay between community dynamics and habitat structure across temporal and spatial scales. Here we develop formulas that characterise extinction debt in a spatial neutral model after habitat loss and fragmentation. Central to our formulas are two new metrics, which depend on properties of the taxa and landscape: ‘effective area’, measuring the remaining number of individuals and ‘effective connectivity’, measuring individuals’ ability to disperse through fragmented habitat. This formalises the conventional wisdom that habitat area and habitat connectivity are the two critical requirements for long‐term preservation of biodiversity. Our approach suggests that mechanistic fragmentation metrics help resolve debates about fragmentation and species loss.     

Empirical assessment of the relation between ecological connectivity and land complexity based on information-theoretic metrics

Habitat fragmentation and connectivity loss pose significant threats to biodiversity at both local and landscape levels. Strategies to increase ecological connectivity and preserve strong connectivity are important for dealing with the potential threat of habitat degradation. Various metrics have been used to measure (i.e., quantify) landscape composition and configuration in landscape ecology. However, their relationship with ecological connectivity must be understood to interpret landscape patterns comprehensively. In the present study, correlations between ecological connectivity and land complexity are examined based on information-theory metrics. Two primary questions are explored: (1) to what extent are landscape mosaic measures of entropy correlated with ecological connectivity, with landscape gradient-based measures, and with each other? (2) are landscape gradient-based entropy measures correlated with ecological connectivity more than discrete entropy measures? Results show that all information theoretic metrics are statistically significant (p < 0.05) for modelling ecological connectivity. Among categorically-based indices, the relationship between ECI and joint entropy was the most significant, while a generalized additive model indicated that Boltzmann entropy could predict the ecological connectivity index, explaining ∼60% of the variance. Therefore, configurational entropy can be used for improving ecological connectivity models.     

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 guiña (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 guiñas 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 guiñas. The camera-trap survey data comprised 4168 camera-trap days and 112 independent records of guiñas. 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 guiñas 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 guiñas have a broader niche than previously believed. Additionally, the guiña 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 guiña populations are no longer viable.     

Accounting for the causal basis of collinearity when measuring the effects of habitat loss versus habitat fragmentation

Collinearity among metrics of habitat loss and habitat fragmentation is typically treated as a nuisance in landscape ecology, and it is the norm to use statistical approaches that remove collinear information prior to estimating model parameters. However, collinearity may arise from causal relationships among landscape metrics and may therefore signal the occurrence of indirect effects (where one model predictor influences the response variable by driving changes in another influential predictor). Here we suggest that, far from being merely a statistical nuisance, collinearity may be crucial for accurately quantifying the effects of habitat loss versus habitat fragmentation. We use simulation modelling to create datasets of collinear landscape metrics in which collinearity arose from causal relationships, then test the ability of two statistical approaches to estimate the effects of these metrics on a simulated response variable: 1) multiple regression, which statistically removes collinearity, and was identified in a recent study as the best approach for estimating the effects of collinear landscape metrics (although this study did not account for any indirect effects implied by collinearity among metrics); and 2) path analysis, which accounts for the causal basis of collinearity. In agreement with this previous study, we found that multiple regression gave unbiased estimates of direct effects (effects not mediated by other model predictors). However, it gave biased estimates of total (direct + indirect) effects when indirect effects occurred. In contrast, path analysis reliably identified the causal basis of collinearity and gave unbiased estimates of direct, indirect, and total effects. We suggest that effective research on the impacts of habitat loss versus fragmentation will often require tools that can empirically test whether collinear landscape metrics are causally related, and if so, account for the indirect effects that these causal relationships imply. Path analysis, but not multiple regression, provides such a tool.