Poesch, M.S. and D.A. Jackson (2012) Addressing the removal of rare species in multivariate bioassessments: the impact of methodological choices. Ecological Indicators 18: 82-90.

Citation: Poesch, M.S. & Jackson, D.A. 2012. Addressing the removal of rare species in multivariate bioassessments: the impact of methodological choices. Ecological Indicators 18: 82-90.

Abstract

Multivariate analyses are important tools for the biological assessment of ecological communities. Despite the popularity of multivariate analyses in bioassessments, there is considerable controversy over how to treat rare species. As this debate remains unresolved, the objective of this study was to develop a methodology to quantify the impacts of removing rare species relative to other decisions inherent in multivariate analyses and to provide insight into their relative influence in our studies. Using fish species from a well-sampled system, we assessed the impact of several choices common to multivariate analyses, including the removal of rare species, ordination technique and measures of multivariate resemblance. Comparisons of multivariate analyses demonstrated the choice of ordination method explained 26% of the variation among the various results, followed by the choices regarding the removal of rare species (24.8%) and resemblance measure (11%). At the same time, the removal of rare species had important site-level impacts relative to full dataset, including a >9 fold change in sites impacted by the removal of single species, with an emphasis on removing species more correlated to anthropogenic stress. Our study demonstrates that the removal of rare species had similar or greater influence in multivariate analyses as other choices inherent in their calculation, such as the choice of ordination method. Better justifications for the removal of rare species, along with all decisions in multivariate analyses, are needed to move bioassessments forward.

Poesch, M.S. and D.A. Jackson (2012) Impact of species-specific dispersal and regional stochasticity on estimates of population viability in stream metapopulations. Landscape Ecology 27: 405-416.

Citation: Poesch, M.S. & Jackson, D.A. 2012. Impact of species-specific dispersal and regional stochasticity on estimates of population viability in stream metapopulations. Landscape Ecology 27: 405-416.

Abstract

Species dispersal is a central component of metapopulation models. Spatially realistic metapopulation models, such as stochastic patch-occupancy models (SPOMs), quantify species dispersal using estimates of colonization potential based on inter-patch distance (distance decay model). In this study we compare the parameterization of SPOMs with dispersal and patch dynamics quantified directly from empirical data. For this purpose we monitored two metapopulations of an endangered minnow, redside dace (Clinostomus elongatus), using mark-recapture techniques across 43 patches, re-sampled across a 1 year period. More than 2,000 fish were marked with visible implant elastomer tags coded for patch location and dispersal and patch dynamics were monitored. We found that species-specific dispersal and distance decay models provided qualitatively similar rankings of viable patches; however, there were differences of several orders of magnitude in the estimated intrinsic mean times to extinction, from 24 and 148 years to 362 and >100,000 years, depending on the population. We also found that the rate of regional stochasicity had a dramatic impact for the estimate of species viability, and in one case altered the trajectory of our metapopulation from viable to non-viable. The divergent estimates in time to extinction times were likely due to a combination species-specific behavior, the dendritic nature of stream metapopulations, and the rate of regional stochasticity. We demonstrate the importance of developing comparative analyses using species- and patch-specific data when determining quantitative estimates for mean time to extinction, which in the case of redside dace, were highly sensitive to different estimates of dispersal.

Poesch, M.S., Lawrie, D., Tu, C., Jackson, D.A., and N.E. Mandrak (2012) Developing local and regional population estimates for an endangered freshwater minnow, the redside dace (Clinostomus elongatus), in Canada. Aquatic Conservation 22: 47-57.

Citation: Poesch, M.S., Lawrie, D., Tu, C., Jackson, D.A., and N.E. Mandrak. 2012. Developing local and regional population estimates for an endangered freshwater minnow, the redside dace (Clinostomus elongatus), in Canada. Aquatic Conservation 22: 47-57. 

Abstract

The Laurentian Great Lakes have undergone drastic declines in freshwater fishes, with 22 species having become extinct in the past century and many more currently at risk. One such species is the endangered minnow, the redside dace (Clinostomus elongatus), which is undergoing severe declines across its entire range. Depletion and mark–recapture surveys were used to quantify population estimates of redside dace at several spatial scales (pool, reach and catchment) across several Great Lakes tributaries in Canada. There was large variation in the local population estimates and the rate of occurrence of redside dace populations. In some cases, such as Gully Creek, a Lake Huron tributary, redside dace were widespread (9/10 of pools) but in low abundances (13.5 individuals per pool ± 5.09 ). In other cases, such as in the Don River, redside dace were highly localized (2/27 pools) but in relatively high abundance (99.2 individuals/pool ± 18.1). Extrapolated population estimates at the catchment scale showed that three of the five study populations were below conservative estimates needed for long-term population viability. Differences in redside dace populations were driven by adjacent land-use. Post-hoc analyses revealed strong negative associations between population estimates and impervious land-use (i.e. urbanization) at both the pool and sub-catchment level. Immediate recovery actions that will focus on eliminating chronic and episodic impacts of adjacent land-use and improve connectivity are needed to help ensure redside dace, like many freshwater species in the Laurentian Great Lakes, remain a species at risk of – rather than facing – extinction.

Schwalb, A.J., Cottenie, K., Poesch, M.S., and J. Ackerman (2011) Dispersal limitation in unionid mussels and implications for their recovery. Freshwater Biology 56: 1509-1518.

Citation: Schwalb, A.J., Cottenie, K., Poesch, M.S., and Ackerman, J. 2011. Dispersal limitation in unionid mussels and implications for their recovery. Freshwater Biology 56: 1509-1518. 

Abstract

Freshwater unionid mussels are a highly imperilled group. Their dispersal abilities depend on the availability and the movement of host fish on which their parasitic mussel larvae develop. We examined the relationship between the dispersal abilities of unionid mussels and their conservation status on a regional (SW Ontario) scale and their distribution and abundance on a catchment scale (Sydenham River, SW Ontario) by determining host specificity and estimating the dispersal abilities of mussels on fish from a review of the literature. On the regional scale, we found that mussels with the most precarious conservation status relied on host fish with short movement distances, whereas vulnerable and more secure mussel species had host fish with 2–3 orders of magnitude larger movement distances. We were not able to detect a clear pattern on the catchment scale. Our results suggest that limited dispersal by host fish affects the abundance and distribution of unionid mussels and ultimately their conservation status on a regional scale. Information on dispersal limitations because of differences in host fish communities should be included in conservation and management decisions to ensure connectivity and maintain functioning mussel metacommunities.

Schwalb, A.J., Poesch, M.S., and J. Ackerman (2011) Movement of logperch—the obligate host fish for endangered snuffbox mussels: implications for mussel dispersal. Aquatic Sciences 73: 223-231.

Citation: Schwalb, A.J., Poesch, M.S., and Ackerman, J. 2011. Movement of logperch—the obligate host fish for endangered snuffbox mussels: implications for mussel dispersal. Aquatic Sciences 73: 223-231.

Abstract

Unionid mussels are highly imperiled and the survival of their local populations is linked to the availability and dispersal potential of their host fish. We examined the displacement distance of logperch (Percina caprodes), which are obligate host fish for endangered snuffbox mussels (Epioblasma triquetra), to determine the dispersal potential by fish. Logperch in the Sydenham River, Ontario, Canada, were electrofished and marked with visible implant elastomer on five sampling dates during the gravid period of E. triquetra. The majority of all recaptures (82%) of P. caprodes occurred within 30 m of their original capture location, with a mean displacement distance of 13 ± 3 m (mean ± standard error, n = 28). These results were consistent with a review of movement studies of small benthic host fish (i.e., darters and sculpins), which revealed average fish displacement distances of 37 ± 19 m (n = 14 species; range: 4–275 m). However, significantly greater movement distances were also found and the maximum displacement distance increased significantly with the spatial extent of the study and with the duration of the study. These results indicate that many P. caprodes remain in a small area, which could restrict the dispersal and (re)colonization potential of E. triquetra. Further studies are needed to determine the dispersal potential of mussels via host fish, which may be important for maintaining the connectivity among unionid populations.

Poesch, M.S., Dextrase, A.J., Schwalb, A.N., and J. Ackerman (2010) Secondary invasion of the round goby into high diversity Great Lakes tributaries and species at risk hotspots: Potential new concerns for endangered freshwater species. Biological Invasions 12: 1269-1284.

Citation: Poesch, M.S., Dextrase, A.J., Schwalb, A.N., and Ackerman, J. 2010. Secondary invasion of the round goby into high diversity Great Lakes tributaries and species at risk hotspots: Potential new concerns for endangered freshwater species. Biological Invasions 12: 1269-1284. 

Abstract

The round goby (Neogobius melanostomus) first invaded North America in 1990 when it was discovered in the St. Clair River. Despite more than 15 years of potential invasion, many Great Lakes’ lotic systems remained uninvaded. Recently, we captured the round goby from several Great Lakes tributaries known as species-at-risk hotspots. With a combination of field sampling of round gobies and literature review of the impact of round gobies on native taxa, we assess the potential impacts of the secondary invasion to native species using three mechanisms: competition; predation; and indirect impacts from the loss of obligate mussel hosts. We estimate that 89% (17/19) of benthic fishes and 17% (6/36) of mussels that occur in these systems are either known or suspected to be impacted by the secondary invasion of round goby. In particular, we note that the distribution of potential impacts of round goby invasion was largely associated with species with a conservation designation, including seven endangered species (1 fish, 6 mussels). As these recent captures of round goby represent novel occurrences in high diversity watersheds, understanding the potential impacts of secondary invasion to native biota is fundamental to prevent species declines and to allow early mitigation.

Featured In: Fisheries 34(9): 421 (Link), & several media outlets.

Poesch, M.S., Walker, S.C., and D.A. Jackson (2009) Functional diversity indices can be driven by methodological choices and species richness. Ecology 90(2): 341-346.

Citation: Poesch, M.S., Walker, S.C., and Jackson, D.A. 2009. Functional diversity indices can be driven by methodological choices and species richness. Ecology 90(2): 341-346.

Abstract

Functional diversity is an important concept in community ecology because it captures information on functional traits absent in measures of species diversity. One popular method of measuring functional diversity is the dendrogram-based method, FD. To calculate FD, a variety of methodological choices are required, and it has been debated about whether biological conclusions are sensitive to such choices. We studied the probability that conclusions regarding FD were sensitive, and that patterns in sensitivity were related to alpha and beta components of species richness. We developed a randomization procedure that iteratively calculated FD by assigning species into two assemblages and calculating the probability that the community with higher FD varied across methods. We found evidence of sensitivity in all five communities we examined, ranging from a probability of sensitivity of 0 (no sensitivity) to 0.976 (almost completely sensitive). Variations in these probabilities were driven by differences in alpha diversity between assemblages and not by beta diversity. Importantly, FD was most sensitive when it was most useful (i.e., when differences in alpha diversity were low). We demonstrate that trends in functional-diversity analyses can be largely driven by methodological choices or species richness, rather than functional trait information alone.

Poesch, M.S., Mandrak, N.E., and R. L. McLaughlin (2008) A practical framework for selecting among single species, multi-species and ecosystem-based recovery plans. Canadian Journal for Fisheries & Aquatic Science 65: 2656-2666.

Citation: Poesch, M.S., Mandrak, N.E., and McLaughlin, R.L. 2008. A practical framework for selecting among single species, multi-species and ecosystem-based recovery plans. Canadian Journal for Fisheries & Aquatic Science 65: 2656-2666.

Abstract

Science-based approaches for selecting among single-species, community-, and ecosystem-based recovery plans are needed to conserve imperilled species. Selection of recovery plans has often been based on past success rates with other taxa and systems or on economic cost, but less on the ecology of the system in question. We developed a framework for selecting a recovery plan based on the distributions and ecology of imperilled and nonimperilled species across available habitat types and applied it to fishes in the Sydenham River, Ontario, Canada. We first tested whether distributions of fishes were adequately predicted by habitat features hypothesized to limit the distributions of imperilled fishes versus a broader set of habitat features known to predict fish distributions. We then tested whether imperilled species occurred in similar or disparate habitat types. For the Sydenham River, an ecosystem-based recovery plan was deemed most appropriate because imperilled species occur in disparate habitat types. We lastly provide decision criteria to facilitate applications of our framework to the selection of recovery plans for other species and systems.

Walker, S., Poesch, M.S. and D. A. Jackson. (2008) Functional rarefaction: Estimated functional diversity from field data. Oikos 117(2): 286-296.

Citation: Walker, S., Poesch, M.S. and Jackson, D.A. 2008. Functional rarefaction: Estimated functional diversity from field data. Oikos 117(2): 286-296.

Abstract

Studies in biodiversity-ecosystem function and conservation biology have led to the development of diversity indices that take species’ functional differences into account. We identify two broad classes of indices: those that monotonically increase with species richness (MSR indices) and those that weight the contribution of each species by abundance or occurrence (weighted indices). We argue that weighted indices are easier to estimate without bias but tend to ignore information provided by rare species. Conversely, MSR indices fully incorporate information provided by rare species but are nearly always underestimated when communities are not exhaustively surveyed. This is because of the well-studied fact that additional sampling of a community may reveal previously undiscovered species. We use the rarefaction technique from species richness studies to address sample-size-induced bias when estimating functional diversity indices. Rarefaction transforms any given MSR index into a family of unbiased weighted indices, each with a different level of sensitivity to rare species. Thus rarefaction simultaneously solves the problem of bias and the problem of sensitivity to rare species. We present formulae and algorithms for conducting a functional rarefaction analysis of the two most widely cited MSR indices: functional attribute diversity (FAD) and Petchey and Gaston’s functional diversity (FD). These formulae also demonstrate a relationship between three seemingly unrelated functional diversity indices: FAD, FD and Rao’s quadratic entropy. Statistical theory is also provided in order to prove that all desirable statistical properties of species richness rarefaction are preserved for functional rarefaction.