Monitoring multiple species: Estimating state variables and exploring the efficacy of a monitoring program

Monitoring programs have the potential to identify population declines and differentiate among the possible cause(s) of these declines. Recent criticisms regarding the design of monitoring programs have highlighted a failure to clearly state objectives and to address detectability and spatial sampling issues. Here, we incorporate these criticisms to design an efficient monitoring program whose goals are to determine environmental factors which influence the current distribution and measure change in distributions over time for a suite of amphibians. In designing the study we (1) specified a priori factors that may relate to occupancy, extinction, and colonization probabilities and (2) used the data collected (incorporating detectability) to address our scientific questions and adjust our sampling protocols. Our results highlight the role of wetland hydroperiod and other local covariates in the probability of amphibian occupancy. There was a change in overall occupancy probabilities for most species over the first three years of monitoring. Most colonization and extinction estimates were constant over time (years) and space (among wetlands), with one notable exception: local extinction probabilities for Rana clamitans were lower for wetlands with longer hydroperiods. We used information from the target system to generate scenarios of population change and gauge the ability of the current sampling to meet monitoring goals. Our results highlight the limitations of the current sampling design, emphasizing the need for long-term efforts, with periodic re-evaluation of the program in a framework that can inform management decisions.     

Patterns of species change in anthropogenically disturbed forests of Madagascar

Five main conclusions arise from this review of the responses of species to anthropogenic disturbance in Madagascar: First, species’ reactions to anthropogenic disturbance are generally negative, but remain poorly known. Our knowledge is patchy among and within higher taxonomic groups; we are still largely gathering case studies. Second, taxonomic groups vary considerably in which proximate factors are most important. Third, several groups show differing responses within different ecoregions. Whether these differences are consistent across groups requires further testing. Fourth, related species often have divergent reactions to disturbance, even within lower taxonomic groupings (families or genera). Thus, we cannot rely on phylogenetic relatedness or even ecological similarity to infer similarity in responses. Finally, disturbance typically reduces species diversity (especially of native and/or endemic species), but also causes species turnover, typically with forest specialists replaced by grassland generalists, and endemics replaced by non-endemics (including invasives). Given these knowledge gaps, we stress the urgency of applied studies that assess species’ ecology, behaviour and health across disturbance gradients, including purely anthropogenic landscapes. Remaining natural vegetation and protected areas will be unable to preserve Madagascar’s biodiversity under the impact of climatic change; we must understand responses of plants and animals to disturbance in order to create buffer zones and corridors combining secondary, degraded and natural habitats.     

甘孜和凉山地区两栖类和爬行类动物多样性研究

对四川省西部甘孜凉山地区的两栖爬行动物进行了调查研究,结合文献资料,该地区现已知两栖爬行动物共121种。其中,两栖动物57种,隶属于2目10科18属;爬行动物64种,隶属于2目9科32属。该地区物种组成较为丰富,区系组成以东洋种为主,特有种所占比例较高。     

Characteristics of small headwater wetlands in second-growth forests of Washington, USA

In 2002, we initiated a study to clarify the response of headwater catchments to logging on timberlands in the Coast Range of Washington, USA. Most of the predominantly first-order streams studied (summer low flows typically < 0.3 L s⁻¹) were hydrologically complex, consisting of a main surface channel connected to multiple, small wetlands. To better understand the forest management implications of headwater systems with two surface hydrology components of potentially differing areal extents (i.e., broad wetlands and narrow, channelized flow), we examined in more detail the wetlands associated with 30 headwater channels. On average, 2.3 wetlands occurred per channel. All 68 surveyed wetlands were, individually, smaller than 0.1 ha, which is a minimum survey-and-manage size criterion for forested wetlands in use in the Pacific Northwest. Seventy-nine percent of the wetlands surveyed by the full-triad method met regional wetland triad criteria for wetland delineation (qualifying wetland soils, hydrology, and vegetation indicators). These headwater wetlands were associated with several landscape variables: (1) northerly-facing catchments, (2) perennial surface water, and (3) down, channel-associated large wood originating from adjacent riparian forest. Our results show that small forested wetlands are quite common and that the surface area of small wetlands can rival the surface area of the associated first-order streams. This initial effort to quantify characteristics of small headwater wetlands suggests small wetlands could dominate or influence headwater surface area processes including those associated with stream responses to disturbances such as logging.     

Amphibian distributions in riparian and upslope areas and their habitat associations on managed forest landscapes in the Oregon Coast Range

Over the past 50 years, forested landscapes of the Pacific Northwest have become increasingly patchy, dominated by early successional forests. Several amphibian species associated with forested headwater systems have emerged as management concerns, especially after clearcutting. Given that headwater streams comprise a large portion of the length of flowing waterways in western Oregon forests, there is a need to better understand how forest management affects headwater forest taxa and their habitats. Mitigation strategies include alternatives to clearcutting, such as harvests that remove only part of the canopy and maintenance of riparian buffer strips. Our study investigates effects of upland forest thinning coupled with riparian buffer treatments on riparian and upland headwater forest amphibians, habitat attributes, and species-habitat associations. Amphibian captures and habitat variables were examined 5–6 years post-thinning within forest stands subject to streamside-retention buffers and variable-width buffers, as well as unthinned reference stands. We found no treatments effects, however, our results suggest that ground surface conditions (e.g., amount of rocky or fine substrate) play a role in determining the response of riparian and upland amphibians to forest thinning along headwater streams. Distance from stream was associated with amphibian abundance, hence retention of riparian buffers is likely important in maintaining microclimates and microhabitats needed for amphibians and other taxa. Moderate thinning and preservation of conditions in riparian and nearby upland areas by way of variable-width and streamside-retention buffers may be sufficient to maintain suitable habitat and microclimatic conditions vital to amphibian assemblages in managed headwater forests.     

Choosing the survivors? A GIS-based triage support tool for micro-endemics: Application to data for Mexican amphibians

Given the current speed of land use change, we cannot expect to save all species from extinction, and so must decide how to focus limited resources to prevent the greatest number of extinctions. This paper proposes a simple conservation triage method that: evaluates the threat status for 145 micro-endemic Mexican amphibian species; assesses current potential threat abatement responses derived from existing policy instruments and social initiatives; and combines both indicators to provide broad-scale conservation strategies that would best suit amphibian micro-endemic buffered areas (AMBAs) in Mexico. To prioritize the AMBAs we used existing and newly compiled spatial databases of territorial conservation instruments, threats, and amphibian range distributions for Mexico. We identify 50% of Mexican micro-endemic amphibians as requiring urgent actions. Based on the location of the AMBAs and using existing conservation instruments, we develop a conservation strategy for the majority of these species. However, almost 25% urgently need field-base verification to confirm their persistence due to the small percentage of remnant natural vegetation within the AMBAs, before we may sensibly recommend such a strategy.     

Monitoring distributions using call surveys: estimating site occupancy, detection probabilities and inferring absence

Monitoring programs serve to track changes in the distribution and abundance of species. A major problem with most monitoring programs is that species detection is imperfect and some populations are inevitably missed. Therefore, in most monitoring programs the true distribution of a species will be underestimated. Here, we report a field test of the reliability and performance of a commonly used method to monitor the distribution of amphibians (anuran call surveys). We surveyed the distribution of four anuran species in western Switzerland, and estimated detection probabilities to account for imperfect species detection and used these estimates to adjust our estimate of site occupancy (i.e., distribution). Next, we assessed how detection probabilities were affected by weather and how site occupancy was affected by site specific covariates. For one species (Hyla arborea), call surveys proved efficient in determining the regional distribution with only few site visits because detection probabilities were relatively high. The call surveys apparently missed many populations of another common species (Bufo calamita) because detection probabilities were lower. Two other species (Bombina variegata and Alytes obstetricans) were uncommon and strong inference from the analysis is not possible. Thus, multispecies surveys may be inefficient for rare species. Estimates of detection probabilities were used to calculate how many site visits are necessary to infer the absence of a species with some predetermined statistical certainty. The implications of “false absences” are important in ecology as they are known to bias usual habitat suitability models and overestimate extinction/colonization events in metapopulations. Large-scale monitoring programs would benefit from the application of an estimation-based approach to monitoring the distribution of species.     

Altered drying regime controls distribution of endangered salamanders and introduced predators

Introduction of invasive species has been implicated in the decline of many native species. However, the mechanisms that underlie successful invasion and species replacement are often poorly understood. We tested the hypothesis that disruption of the natural disturbance regime can facilitate invasion of habitats, resulting in the exclusion of native species. In Arizona’s San Rafael Valley, cattle ponds designed to hold water year-round have replaced seasonal marshes, and this altered drying regime has facilitated invasion by disturbance-intolerant fish and bullfrogs that negatively affect native Sonoran tiger salamanders. We investigated the relationships among pond drying regime, presence of introduced fish and bullfrogs, and presence of tiger salamander populations in 42 ponds. Both fish and breeding bullfrog populations disappeared following pond drying. Pond drying in cattle ponds negatively affected salamanders, but not to the same extent that it affected fish and bullfrogs. Metamorphosed bullfrogs ate salamander larvae in laboratory and field experiments, and the risk of local extinction among salamander populations was increased by introduced fish. Once fish eliminated salamanders from an aquatic habitat, salamanders seldom reappeared unless fish were killed by drying. Simple models were developed to predict change in salamander, fish, and bullfrog distributions with changes in cattle pond drying frequency. The models show that decreases in pond drying frequency could negatively affect salamanders by leading to a community dominated by disturbance-intolerant fish and bullfrogs, but increased drying frequency could negatively affect salamander populations by preventing salamander breeding. These results suggest that manipulation or restoration of disturbance regimes may be a powerful tool in managing for native species threatened by biotic invasions.