Christopher R. Field

Quantifying the importance of geographic replication and representativeness when estimating demographic rates, using a coastal species as a case study

Demographic rates are rarely estimated over an entire species range, limiting empirical tests of ecological patterns and theories, and raising questions about the representativeness of studies that use data from a small part of a range. The uncertainty that results from using demographic rates from just a few sites is especially pervasive in population projections, which are critical for a wide range of questions in ecology and conservation. We developed a simple simulation to quantify how this lack of geographic representativeness can affect inferences about the global mean and variance of growth rates, which has implications for the robust design of a wide range of population studies. Using a coastal songbird, saltmarsh sparrow (Ammodramus caudacutus), as a case study, we first estimated survival, fecundity, and population growth rates at 21 sites distributed across much of their breeding range. We then subsampled this large, representative dataset according to five sampling scenarios in order to simulate a variety of geographic biases in study design. We found spatial variation in demographic rates, but no large systematic patterns. Estimating the global mean and variance of growth rates using subsets of the data suggested that at least 10-15 sites were required for reasonably unbiased estimates, highlighting how relying on demographic data from just a few sites can lead to biased results when extrapolating across a species range. Sampling at the full 21 sites, however, offered diminishing returns, raising the possibility that for some species accepting some geographical bias in sampling can still allow for robust range-wide inferences. The sub-sampling approach presented here, while conceptually simple, could be used with both new and existing data to encourage efficiency in the design of long-term or large-scale ecological studies. This article is protected by copyright. All rights reserved.

How does choice of statistical method to adjust counts for imperfect detection affect inferences about animal abundance

Summary 1.There is ongoing debate in ecology about the value of the increasing complexity of analytical methods, especially as it relates to models that correct occupancy or abundance estimates for imperfect detection. While both arguments for and against increasing complexity have merit, there is a need for greater clarity on how to determine what level of complexity is necessary. We present a general approach and case study for comparing alternative detection methods that vary in their complexity. Our approach puts emphasis on the logistical costs of methods, which are often overlooked in the debate about method complexity, and on developing models that address common sources of error in ecological datasets while avoiding unwarranted complexity. 2.We used point counts of saltmarsh sparrows (Ammodramus caudacutus) to compare estimates of abundance from three alternative protocols that vary by logistical costs: single observer, multiple observers, and multiple visits. We also compared results from counts to those from captures and nest searches from the same populations to provide broader context for the evaluation of point count methods. 3.We found that parameter estimates derived from alternative count protocols were similar and that predictions of point-level abundance were highly correlated (r = 0.96). We found lower correlation between pairwise comparisons of abundance estimated from point count data, the number of individuals captured, and the number of nests (all comparisons r = 0.5 or less). 4.Choosing point counts over alternative measures of abundance may have a greater effect on inferences than choosing among specific count protocols. For saltmarsh sparrows, there is likely little added benefit to adopting count protocols that require additional logistical costs. Determining the frequency of cases like this has broad implications for the appropriate design of studies that rely on estimates of abundance, especially when resources are limited. The general approach we present can be used to assess whether general rules of thumb can be developed to benefit people charged with implementing field studies and allocating limited resources. This article is protected by copyright. All rights reserved.

Landowner behavior can determine the success of conservation strategies for ecosystem migration under sea-level rise

Significance Key questions remain about the role of social factors, especially the behavior of private landowners, in determining the outcome of strategies for conservation under climate change. We surveyed the behavioral intentions of coastal landowners in the northeast United States, where extreme sea-level rise threatens tidal marsh persistence unless private landowners allow landward marsh migration. Our results identify (i) conservation strategies currently being implemented that may not have enough support among target populations to mitigate losses from sea-level rise, and (ii) beliefs and attitudes that may be effective targets for outreach aimed at increasing participation in these strategies. The importance of these social factors as constraints on marsh migration highlights the need for wider integration into planning for coastal adaptation. The human aspects of conservation are often overlooked but will be critical for identifying strategies for biological conservation in the face of climate change. We surveyed the behavioral intentions of coastal landowners with respect to various conservation strategies aimed at facilitating ecosystem migration for tidal marshes. We found that several popular strategies, including conservation easements and increasing awareness of ecosystem services, may not interest enough landowners to allow marsh migration at the spatial scales needed to mitigate losses from sea-level rise. We identified less common conservation strategies that have more support but that are unproven in practice and may be more expensive. Our results show that failure to incorporate human dimensions into ecosystem modeling and conservation planning could lead to the use of ineffective strategies and an overly optimistic view of the potential for ecosystem migration into human dominated areas.

Evaluating a focal-species approach for tidal marsh bird conservation in the northeastern United States

ABSTRACT Insufficient time and funding remain obstacles to collecting data across broad spatial scales on the fine-scale distribution of multiple species, their life histories, and interactions with other species and the environment. This often necessitates the use of focal species to inform conservation and management decisions. We used the systematic conservation-planning software Marxan to assess quantitatively whether a focal species can aid in conservation and management of tidal marsh birds. Using a metric of relative cost in the region and current protected areas, we identified priority areas for conservation of 5 specialist taxa—Clapper Rail (Rallus crepitans), Eastern Willet (Tringa semipalmata semipalmata), Acadian Nelsons Sparrow (Ammospiza nelsoni subvirgatus), Saltmarsh Sparrow (A. caudacuta), and Seaside Sparrow (A. maritima)—that nest primarily in tidal marshes in the northeastern United States. We compared the spatial prioritization of sites and cost-effectiveness of alternative protection scenarios that considered individual species, groups of species, and all species simultaneously to evaluate the appropriateness of a focal-species approach. Scenarios that prioritized areas for conservation based on single-species targets were poorly correlated across species. Scenarios based on Saltmarsh Sparrow conservation were most strongly related (rs = 0.759) to site prioritizations that considered all 5 tidal marsh specialists simultaneously. When comparing multispecies combinations to prioritizations based on the Saltmarsh Sparrow alone, the estimated costs, area of land protection, and number of individuals of each species protected were similar. These results suggest that no species is a good surrogate for another but that the Saltmarsh Sparrow may be a viable focal species for conservation planning to protect tidal marsh birds as a group. By evaluating protection scenarios for all species, we were able to identify areas where conservation is likely to have little or no effect, which could be as important for decision making as identifying the best sites.

A Pleistocene disturbance event describes modern diversity patterns in tidal marsh birds

There is growing evidence to support that paleo-timescale events are important determinants in the present-day distribution of organisms. We explored the relationship between community composition of tidal marsh birds in the northeastern United States and potential drivers of biodiversity patterns across timescales to explore the relevance of historical contingency in this ecosystem. These potential predictors represent some of the major known influences on biodiversity in tidal marshes, including 1) a recent, intense hurricane event driving a large-scale perturbation of this ecosystem (4 ya), 2) gradual modification of marshes through installation of human infrastructure (~150 ya), and 3) marsh formation and development after the Last Glacial Maximum (LGM, ~20,000 ya). We surveyed >1300 locations in tidal marshes from 2011 - 2014 using passive point count methods to measure bird community composition at these points. We found that rarefied richness, total individuals (N), and total biomass were best explained by a quadratic relationship with marsh age peaking at 40° latitude, the location of the Last Glacial Maximum of the Laurentide ice sheet. We hypothesize that formation of marsh millennia earlier in the southern part of our survey area allowed for earlier evolution of specialization to tidal marsh by bird species than those occupying much younger, northern marshes, which could have then driven differential rates of colonization in the north (by habitat generalists) and competitive exclusion in the south (by habitat specialists). We tested this theory using a novel functional diversity metric (Community Habitat Specialization Index, or CHSI) and find that community specialization decreased linearly with marsh age, supporting our hypothesis. Our findings highlight the importance for consideration of historical contingency in biodiversity research and further exploration of mechanisms operating across geological timescales. This article is protected by copyright. All rights reserved.

Abundance and Temporal Patterns in Wetland Birds in and Around Lake Zeway, Ethiopia

Abundance and Temporal Patterns in Wetland Birds in and Around Lake Zeway, Ethiopia The aim of the study was to describe the abundance and temporal patterns of wetland bird species in and around Lake Zeway, an Important Bird Area and potential Ramsar site in Ethiopia. Nine years of wetland bird data of the area, collected by the African Waterbird Census, were used for the study. Surveys were made to examine the bird abundance, diversity and temporal patterns. We recorded 129 wetland bird species from 23 families; including two globally vulnerable and 6 near threatened species. The results revealed no clear trend or pattern in the abundance of the birds.