Foraging behaviour of a frugivorous bat helps bridge landscape connectivity and ecological processes in a fragmented rainforest

1. Landscape connectivity may greatly influence the distribution of animals when it alters their movements and their ability to reach food patches. Depending on their foraging behaviour, organisms may or may not adapt to anthropogenic changes in landscape connectivity and may eventually undergo local extinctions. 2. Recent studies underlined the need to use indicators of functional landscape connectivity based on the behaviour and movement abilities of studied animals to better link landscape structure to ecological processes in disturbed and fragmented areas. 3. The objectives of this study were: to elaborate an index of functional connectivity for Rhinophylla pumilio, a Neotropical understorey frugivorous bat; to use this index to investigate the possible mechanisms controlling its distribution and sustainability in a fragmented landscape; and to test whether this index could be applied to other species of the same guild. 4. We pursued a 10-year bat mist-net survey, coupled to local estimates of food availability, in a mature forest of French Guiana that was recently fragmented by the completion of a reservoir lake. The 18 sampling sites range from undisturbed continuous forest sites to small remote forest fragments. A connectivity value, based on radio-tracking surveys, was attributed to each site. Connectivity measures mean forest cover within neighbouring landscape units, weighted by the probability that bats would use them, as estimated by frequency distribution of flight distance data. 5. The abundance of R. pumilio was positively correlated with landscape connectivity and not correlated with local food availability. Its foraging strategy has evolved in response to the highly scattered distribution of its fruit resource. In spite of its high mobility, R. pumilio apparently failed to exploit a food resource that is distributed patchily over a low-connective habitat because its foraging movements are not well adapted to habitat disruptions. 6. The connectivity index contributed to explain general tendencies of abundance variations in other understorey frugivorous bats, although the spatial scale we examined was probably too small for these species. We make recommendations to adapt a functional connectivity index to species whose large-scale movements are difficult to survey.     

景观连接度的概念、度量及其应用

景观连接度是指景观促进或阻碍生物体或某种生态过程在源斑块间运动的程度,反映了景观的功能特征。景观连接度理论与方法是景观评价、管理和生态规划的重要基础,对于区域可持续发展和生物多样性保护等方面的研究都具有重要指导意义。综述了国内外近10a来有关景观连接度概念、度量方法及其生态学意义的最新进展,并探讨了景观连接度与景观要素间的关系及其潜在应用前景,以期为深入开展景观空间格局与生态过程间关系的研究与应用提供参考。     

Multi‐scale effects of impoundments on genetic structure of creek chub (Semotilus atromaculatus) in the Kansas River basin

1. Habitat fragmentation has been implicated as a primary cause for the ongoing erosion of global biodiversity, yet our understanding of the consequences in lotic systems is limited for many species and regions. Because of harsh environmental conditions that select for high colonisation rates, prairie stream fishes may be particularly vulnerable to the effects of fragmentation. Hence, there is urgent need for broader understanding of fragmentation in prairie streams such that meaningful conservation strategies can be developed. Further, examination at large spatial scales, including multiple impoundments and un‐impounded catchments, will help identify the spatial extent of species movement through the landscape. 2. Our study used data from 10 microsatellite loci to describe the genetic structure of creek chub (Semotilus atromaculatus) populations across four catchments (three impounded and one un‐impounded) in the Kansas River basin. We investigated whether genetic diversity was eroded in response to habitat fragmentation imposed by reservoirs and whether intervening lentic habitat increased resistance to dispersal among sites within a catchment. 3. Our analyses revealed that genetic diversity estimates were consistent with large populations regardless of the location of the sampled tributaries, and there was little evidence of recent population reductions. Nevertheless, we found a high degree of spatial genetic structure, suggesting that catchments comprise a set of isolated genetic units and that sample sites within catchments are subdivided into groups largely defined by intervening habitat type. Our data therefore suggest that lentic habitat is a barrier to dispersal among tributaries, thus reducing the opportunity for genetic rescue of populations in tributaries draining into reservoirs. Isolation by a reservoir, however, may not be immediately deleterious if the isolated tributary basin supports a large population.     

The effect of cost surface parameterization on landscape resistance estimates

A cost or resistance surface is a representation of a landscape's permeability to animal movement or gene flow and is a tool for measuring functional connectivity in landscape ecology and genetics studies. Parameterizing cost surfaces by assigning weights to different landscape elements has been challenging however, because true costs are rarely known; thus, expert opinion is often used to derive relative weights. Assigning weights would be made easier if the sensitivity of different landscape resistance estimates to relative costs was known. We carried out a sensitivity analysis of three methods to parameterize a cost surface and two models of landscape permeability: least cost path and effective resistance. We found two qualitatively different responses to varying cost weights: linear and asymptotic changes. The most sensitive models (i.e. those leading to linear change) were accumulated least cost and effective resistance estimates on a surface coded as resistance (i.e. where high-quality elements were held constant at a low-value, and low-quality elements were varied at higher values). All other cost surface scenarios led to asymptotic change. Developing a cost surface that produces a linear response of landscape resistance estimates to cost weight variation will improve the accuracy of functional connectivity estimates, especially when cost weights are selected through statistical model fitting procedures. On the other hand, for studies where cost weights are unknown and model selection is not being used, methods where resistance estimates vary asymptotically with cost weights may be more appropriate, because of their relative insensitivity to parameterization.     

人为干扰对神农架川金丝猴连通性及遗传多样性的影响

川金丝猴湖北种群是川金丝猴分布的最东缘,现主要分布于神农架国家公园和巴东自然保护区,其作为单独的管理单元,相对较低的遗传多样性、孤立的遗传状态和较小的种群数量,使得该种群面对环境变化脆弱性高。以神农架为研究区域,首先基于物种分布模型获得川金丝猴移动的阻力图层,利用电路理论分析适宜生境连接度;其次,设置道路和旅游两个人为干扰情景,运用最小费用距离模型与电路理论模型,分析道路和旅游活动对川金丝猴移动路径以及对不同亚群内和亚群间连通性的影响;最后,利用CDPOP软件模拟道路对川金丝猴遗传多样性的影响。结果表明:(1)神农架川金丝猴适宜生境分布较集中,生境斑块间存在多个潜在扩散区域;(2)道路改变了川金丝猴往来于南北生境间的最优路径,旅游干扰对川金丝猴移动路径无明显影响,其干扰主要在于川金丝猴对其具有回避性,回避距离为100 m;(3)道路显著降低金猴岭亚群内的连通性,并显著增加了所有亚群间的移动阻力,旅游活动对亚群内和亚群间的连通性无显著影响;(4)川金丝猴种群在150年内的遗传多样性呈下降趋势,道路的影响将加剧遗传多样性下降的程度。基于以上结果本文提出了针对性的保护建议,对于该物种的保护和其他濒危物种的类似研究具有较强的参考价值和借鉴意义。