Measuring community responses to large-scale disturbance in conservation biogeography

Aim   Which community metrics should be used to reflect community response to large-scale habitat alterations is unclear. Here, we assess what and how community changes should be measured to accurately track community responses to large-scale disturbance in space and/or time.
Location   France.
Method   We first developed a simulation model to examine temporal changes in the species composition of large-scale metacommunities. Using this model, we assessed how species richness, Shannon index, trends of particular subset of species or community indices of habitat specialization were influenced by different disturbance scenarios, and whether these indices were biased by imperfect detectability. We further used more than 1000 empirical bird communities from the French Breeding Bird Survey recently exposed to disturbances of various intensities as a case study.
Results   Our simulation and empirical results both demonstrate that species richness and diversity measures can show confusing trends and even provide misleading messages of communities' fate. In contrast, reflecting the composition of the community in terms of habitat specialist and generalist species was more robust and powerful to reflect disturbance effects.
Main conclusions   We highlight the weakness of using community metrics that fail to incorporate ecological difference among species when summarizing community-level trends in disturbed landscapes.     

Detectability of American Mink Using Rafts to Solicit Field Signs in a Population Control Context

Abstract: American mink (Neovison vison) are an ecologically damaging invasive species where they have been introduced in Europe. Effectiveness of mink population control by trapping has been difficult to assess, without knowing how efficiently mink are caught by traps or detected by other methods. Use of track-recording rafts to detect mink and guide trapping effort has proved efficient and leads to a supposition that no detection indicates absence of mink. To draw this conclusion with any confidence requires a measure of detectability. We applied occupancy models to data from an earlier study to estimate detectability of individual American mink on track-recording rafts. Estimated detectability of individual mink, per raft, and 2-week check period varied between 0.4 in late summer and 0.6 in late autumn. By inference, risk of failing to detect a mink that was present would be <5% given 4–6 independent opportunities to detect it. These opportunities could be created either by using a raft spacing that ensured multiple detections of each mink or by monitoring rafts through a succession of check intervals. Within certain simple constraints, raft location did not contribute substantially to detection probability. These findings will allow field operators, strategists, and funders to assess with confidence the success of efforts to control mink density. We expect the estimation of individual detectability to be similarly valuable in population control or eradication of other species.     

Bias in aerial estimates of the number of nests in White Ibis and Great Egret colonies

ABSTRACT Estimating detection error, as well as the magnitude of other potential survey biases, is essential when sampling efforts play a role in the estimation of population size and management of wildlife populations. We quantified visual biases in aerial surveys of nesting wading birds (Ciconiiformes) in colonies in the Florida Everglades using a negative binomial count regression model to compare numbers of nests in quadrats counted on the ground with numbers estimated from aerial photographs of the same quadrats. The model also allowed the determination of degree of difference between monitoring results based upon such factors as nest density, vegetative cover, and nest turnover rates. Aerial surveys of White Ibis (Eudocimus albus) colonies underestimated the true number of nests found during ground counts by 11.1%, and underestimates were significantly greater (P= 0.047) in a colony with high nest turnover. Error rates did not differ for quadrats that varied in the density of White Ibis nests did not differ, and visual bias did not increase with vegetative complexity (P= 0.73). Estimates of nest density in colonies of Great Egrets (Ardea alba) based on aerial surveys were higher than ground counts for 38% of the quadrats sampled, and mean visual bias was 23.1%. Species misidentification likely contributed to visibility bias for Great Egrets in our study, with some Snowy Egrets almost certainly mistaken for Great Egrets in aerial photos. Biases of the magnitude we observed fro Great Egrets and White Ibises can mask true population trends in long‐term monitoring and, therefore, we recommend that detection probability be explicitly evaluated when conducting aerial surveys of nesting birds.     

Influence of larval dietary supply on the food consumption, food utilization efficiency, growth and development of the lacewingChrysoperla carnea

In order to derive quantitative estimates of predation rate from serological gut analysis data, one must have an estimate of the interval during which a meal can be detected after feeding. In practice this has turned out to be ‘D_max,’ defined as ‘...the time from finishing a meal until that meal could just no longer be detected in any individuals.’ However D_max substitutes an absolute limit for what is really a continuous variable with significant variation. We examined this problem in a study of the detectability ofHelicoverpa zea Boddie (Lepidoptera: Noctuidae) fifth instar remains in the guts ofPolistes metricus Say (Hymenoptera: Vespidae). Wasps were maintained onTrichoplusia ni (Hübner) (Lepidoptera: Noctuidae) fifth instars before being fed a singleH. zea fifth instar. They were killed and frozen at 0, 24, 48 and 96 h intervals, with those held for more than 24 h fed a singleT. ni fifth instar at 24 h intervals in order to simulate continued feeding. Wasp abdomens were assayed by immunodot, using a monoclonal antibody toH. zea arylphorin. There was a logarithmic decay in the proportion ofP. metricus positive over time, a singleH. zea fifth instar meal having a detectability half-life of 19.4 h at field temperatures. If prey antigen detectability decays exponentially, then a detectability half-life is a more appropriate unit of detectability than an absolute detectability period.     

Occupancy models including local and landscape variables are useful to assess the distribution of a salamander species at risk

Numerous amphibian species are at risk of extinction worldwide. Therefore, reliable estimations of the distribution and abundance of these species are necessary for their conservation. Generally, amphibians are difficult to detect in the wild, which compromises the accuracy of long-term population monitoring and management. Occupancy models are useful tools to assess how environmental variables, at a local and at a landscape scale, affect the distribution and abundance of organisms taking into account species imperfect detectability. In this study, we evaluated with an environmental multiscale approach the seasonal variation of the occupation area of the threatened salamander, Ambystoma ordinarium along its distribution range. We obtained readings in 60 streams of physicochemical variables associated with habitat quality and landscape features. We found that detection and occupation probability of A. ordinarium are seasonally associated with different environmental variables. During the dry season, detectability was positively associated with temperature and stream depth, whereas occupancy was positively associated with the proportion of crops in the landscape and stream elevation. In the rainy season, the detection probability was not explained by any variable considered, and occupancy was negatively associated with stream's electrical conductivity and dissolved oxygen. Based on the estimation of occupied sites, we showed that A. ordinarium presents a more restricted distribution range than previously projected. Therefore, our results reveal the importance of evaluating the accuracy of distribution estimates for the conservation of threatened species as A. ordinarium.     

Our time will come: Is anuran community structure related to crop age?

An ongoing controversy involves the debate about the effects of man‐made land transformation on freshwater biodiversity. It has been suggested that agricultural areas provide habitats for many species of amphibians, but crop age may affect richness and community structure. In such modified landscapes, a nested structure has been commonly detected, although community structure may be season specific and guild specific. Here, we determined detectability associated with site‐specific and survey‐specific variables and examined nestedness patterns in anuran communities in natural areas and rice fields with different crop ages (10 and 20 years) in southern Brazil. We studied whether nestedness was associated with time since cultivation and whether these patterns were similar across guilds in these areas. Anuran detectability was related only with time after sunset. Community composition varied between crop ages. Aquatic and arboreal species were associated with native areas and showed a nested pattern. Fossorial species did not show significant nestedness. Our results showed that factors associated with crop age may affect guilds in different ways. These effects seem to be related to individual traits of species (habitat preferences, reproductive modes, plasticity). Incorporating species traits may enhance conservation strategies in agroecosystems.     

The landscape configuration and lethality of snare poaching of sympatric guilds of large carnivores and ungulates

Poaching of wildlife presents one of the biggest conservation challenges in the 21st century. Snaring is one of the primary means of capturing target animals. To prioritise interventions intending to reduce snaring, we describe an approach for quantifying the configuration and lethality of snares. We conducted transect surveys in Murchison Falls National Park. All the snares that we recovered were made of wire with the majority (81.0%, n = 546 of 674) deriving from vehicle tire wire. The density of snares ranged from 0.08 to 4.58 snares/km², which is the highest known density in sub‐Saharan Africa. The majority (63%) of the animals caught in wire snares were unrecovered and wasted. We found that noose width, vertical drop, wire circumference, anchor height, proportion of un‐thicketed area, grass height, distance to river and village had a significant positive relationships to lethality, while snare thickness, charms, tree DBH, thicket diameter, distance to nearest road negatively affected lethality. We recommend adopting wholistic anti‐snare countermeasures such as the human heritage‐centred conservation to empower local people. Our method illustrates the opportunity to standardise temporal and spatial measurements of snare density and configuration necessary to stop illegal wildlife poaching.     

Occupancy patterns of an apex avian predator across a forest landscape

Apex predators are integral parts of every ecosystem, having top‐down roles in food web maintenance. Understanding the environmental and habitat characteristics associated with predator occurrence is paramount to conservation efforts. However, detecting top order predators can be difficult due to small population sizes and cryptic behaviour. The endangered Tasmanian masked owl (Tyto novaehollandiae castanops) is a nocturnal predator with a distribution understood to be associated with high mature forest cover at broad scales. With the aim to gather monitoring data to inform future conservation effort, we trialled an occupancy survey design to model masked owl occurrence across ~800 km² in the Tasmanian Southern Forests. We conducted 662 visits to assess masked owl occupancy at 160 sites during July–September 2018. Masked owl site occupancy was 12%, and estimated detectability was 0.26 (±0.06 SE). Cumulative detection probability of masked owls over four visits was 0.7. Occupancy modelling suggested owls were more likely to be detected when mean prey count was higher. However, low detection rates hindered the development of confident occupancy predictions. To inform effective conservation of the endangered Tasmanian masked owl, there is a need to develop novel survey techniques that better account for the ecology of this rare, wide‐ranging and cryptic predator. We discuss the potential to combine novel census approaches that exploit different aspects of masked owl ecology to obtain more robust and detailed data.     

生物物种资源监测原则与指标及抽样设计方法

生物物种资源监测是了解生物物种资源现状、开展生物物种资源保护与管理的基础工作和重要手段.阐述了生物物种资源监测的科学性原则、可操作性原则和持续性原则.提出了监测计划的制定程序;监测计划应充分考虑所具有的人力、资金和后勤保障等条件,并进行定期评估.分析了指示物种在物种资源监测中的作用与不足;认为应选择具有不同生态需求和生活史的生物类群作为监测对象.讨论了监测指标的选取方法;监测指标应可测量、有科学基础、易被公众接受、低成本和高效益;监测方法应具有科学性,能检测到相应的变化,应采用高效率、低成本的标准化监测方法.分析了现有监测计划在抽样设计方面存在的问题,探讨了空间变异性和可检测率对监测数据误差的影响及其处理方式,讨论了样本量确定和监测样地的大小、形状及位置设计.监测样地要有较好的代表性,能在有限的监测面积中较好地反映监测区域内群落种类组成与数量特征.最后,讨论了生物物种资源监测的尺度和标准化问题.