Evaluating and Improving Conservation Practices
The dedication of conservation reserves on an ad hoc basis has been over-turned in recent decades by an enormous volume of research on systematic conservation planning to better represent the full diversity of species, communities, and ecosystems. Despite this research investment, many gaps remain in understanding how we should best identify, acquire, and manage conservation reserves. I have contributed to projects investigating the ability of US National Parks to represent freshwater fish diversity (link and lead author Dave Lawrence) and developing reserve selection procedures proposed to be more robust to climate change (link and collaborators). For my postdoc with Paul Armsworth, I am contributing to a number of projects on the ecological and economic effectiveness of conservation efforts (link). More to follow!
Niche Modeling and Species Invasions
Increased access to species occurrence records, GIS layers of climatic and environmental conditions, and availability of computationally-intensive modeling approaches has resulted in the rapid growth of species distribution or ecological niche models for a diversity of purposes. One common application of these models is characterizing the potential distribution of invasive species for prevention and management. Many ecologists have observed a tendency for native range data to under-estimate known invasive ranges, attributing this either to "niche shifts" with an ecological or evolutionary basis or to the influence of historic events or dispersal barriers that decouple species distributions from abiotic factors. While many studies now investigate such shifts in the climatic (Grinnellian or scenopoetic) niche, fewer researchers make equivalent reciprocal comparisons of the functional (Eltonian or bionomic) niche between native and invasive ranges. Might we expect a species occupying substantially different native and invasive environments to also differ by distribution in its ecological function? Should we anticipate Grinnellian and Eltonian niches to move in synchrony, whether conserved or labile?
With my PhD adviser Julian Olden and collaborator Nisikawa Usio, I used the signal crayfish Pacifastacus leniusculus to simultaneously test for both Grinnellian and Eltonian niche conservatism between the native (Pacific Northwest of North America) and invasive (Japan) range of this species. I found that although the native and invasive ranges of P. leniusculus have dissimilar climates, trophic function of this crayfish, as measured by stable isotopes, was closely conserved between regions. In the case of P. leniusculus, native range data may inadequately predict some areas suitable for invasion, but the broadly omnivorous feeding habits of this species are not a product of the invasion process; they occur in the native range, as well (link). As such, the impacts of P. leniusculus may not be the result of some intrinsic Eltonian niche shift owing to rapid adaptation or enemy release, but rather receiving communities that are not adapted to the conserved function of this generalist arthropod. I also caution that distinctly dispersal-limited species, such as many freshwater organisms, may have poor reciprocal transferability of native and invasive range models.
Given this finding, how might we anticipate the potential ranges for emerging, data-poor invasive species? Pathways of introduction and regions of origin for invasive species change over time, and climate change will continue to shift the regions where invasive species come from and where they can establish. Scientists and resource managers will be challenged to anticipate if these emerging invaders can establish in their jurisdiction when comprehensive invaded range information is absent. In response, I propose documenting the extent of niche elasticity in important climate predictors for well-studied invasive species, and transferring this elasticity as precautionary boundaries for scenarios of niche shifts in emerging data-poor invaders. I term such well-studied invaders “avatars” of niche shift for the emerging species of interest. I recently demonstrated this avatar species concept using both P. leniusculus (above) and the globally invasive red swamp crayfish Procambarus clarkii as avatars of niche shift for the emerging Australian crayfish invader Cherax quadricarinatus. Avatar scenarios of niche shift for C. quadricarinatus more than doubled the global area predicted as suitable for this species relative to models based on its native range alone (link). Many theoretical and applied implications of the avatar species concept require additional investigation, including development of frameworks to select appropriate avatars and evaluating performance of avatar-derived models. However, I believe that my avatar species concept has potential as an important tool in the prevention and management of species invasions, as well as a framework for testing the generality of niche conservatism. I am continuing research on testing and applying the avatar concept to a broader taxonomic and temporal scope.
Crayfish Conservation, Ecology, and Management
My purpose . . . is to exemplify the general truths respecting the development of zoological science; and, to this end, I have selected an animal, the Common Crayfish, which taking it altogether, is better fitted for my purpose than any other. - Thomas Henry Huxley
Crayfish offer limitless opportunities to explore basic and applied questions in freshwater (and terrestrial) ecology. Crayfish are central to aquatic food webs, serving as detritivores, herbivores, predators, and prey. Crayfish are among the most imperiled taxonomic groups in the world with an alarming rate of population and species declines. Crayfish have also produced a number of major invasive species with considerable economic and ecological impacts. Finally, crayfish have value for recreational and commercial harvest and in the aquarium, biological supply, and live seafood industries, yet inadequate effort is exerted to manage their trade, understand the consequences of their exploitation, or discourage their release into the wild. I report new crayfish invasions to facilitate management and awareness (link), test mechanisms by which invasive crayfish may displace native crayfish (link), and I am interested in the potential for life history and ecological traits to predict which crayfishes may be at risk of extinction or invasion in the future (link). I also emphasize education and outreach to prevent the release of invasive crayfish and other freshwater organisms, and I participate in a multi-agency effort addressing aquatic invasive species in biological supply (link).
I am currently interested in the conservation, ecology, and management of crayfishes of the genus Pacifastacus (link). These western North American endemics represent a range of conservation and management challenges, from species that have declined to extinction (Pacifastacus nigrescens) and listing under the Endangered Species Act (Pacifastacus fortis) to a species that has established globally as a major invasive species (Pacifastacus leniusculus). Several other Pacifastacus species lack any field-based evaluation of their conservation status, and the ecological roles of Pacifastacus species in western North American are poorly known, even as these crayfish are being widely replaced by invasive Cambarid crayfishes from eastern North America (link). I have recently published a study that suggests there may be several undescribed species of Pacifastacus in the Pacific Northwest (link), and I am continuing work on the phylogenetics and phylogeography of this genus. I am always looking for collaborators interested in crayfish in western North America, and welcome inquiries and opportunities to learn more about these organisms (contact).
The Thin Blue Line? Exploring Interactions
between Land and Water
Although some ecologists long recognized that aquatic and terrestrial ecosystems are not isolated, effort has intensified in recent years to characterize the flow of energy, nutrients, and organisms between water and land. For example, debate persists over the importance of terrestrial subsidies in supporting aquatic consumers in temperate lakes (link). Most of these studies have prioritized the pelagic (open water) zone while neglecting benthic (lake bottom) processes and organisms. I join others in recognizing and advocating for crayfish as tracers of "land-water ecotonal coupling." Crayfish are relatively long-lived, wide-ranging, and omnivorous, and consequently may integrate and represent available basal resources in aquatic food webs. In addition, many past studies have intensively quantified the contribution of terrestrial subsidies to a small number of similar lakes. I recently used a simple approach based on carbon stable isotopes to instead evaluate the use of terrestrial carbon by the crayfish Pacifastacus leniusculus over a large gradient of lake size (range of 0.13 to 496 km2).
I predicted that like the flow of marine resources to terrestrial islands, the importance of cross-ecosystem subsidies should decrease with increasing habitat size or perimeter:area ratio. My study supported this pattern, but also found an effect of shoreline urbanization (range of 0 to 26 structures/km) on terrestrial carbon dependence. Resource use by P. leniusculus in small, highly urbanized lakes more closely resembled large lakes than small undeveloped lakes (link). Because use of terrestrial carbon by P. leniusculus was unrelated to in-lake productivity (secchi depth range of 2 to 25 m), I hypothesize that this represents a decreased availability of terrestrial carbon rather than a corresponding increase in autochthonous (in-lake) production in urban lakes, although this question merits additional inquiry. This study demonstrated the utility of crayfish as tracers of benthic resource dynamics, confirmed the predicted relationship between habitat area and the importance of terrestrial subsidies to temperate lakes, and documented a way in which human land use may alter basic ecological relationships.
The laboratory of my Masters adviser Dan Magoulick is also interested in the interface between land and water, particularly when streams run dry. Stream drying can occur for a variety of reasons, ranging from predictable seasonal droughts in many arid and semi-arid regions of the world, to extreme supra-seasonal droughts, to human impacts like water diversion and abstraction. Few studies have investigated the behavioral, population, or community responses of aquatic organisms to stream drying. Collaborating with Bob DiStefano at the Missouri Department of Conservation, we demonstrated the persistence of two rare crayfish species through multiple years of severe drying in an Ozark Plateau stream, further confirming the value of intermittent and ephemeral ecosystems for many aquatic species (link). Conversely, I also found that not all crayfish are equally equipped to endure stream drying. For example, laboratory and mesocosm studies revealed that an Ozark endemic crayfish in population decline has poor tolerance of desiccation and drought, while an introduced crayfish that has replaced it in some stream drying-prone reaches is more tolerant to this disturbance (link). These results emphasize the often-overlooked role of abiotic factors in contributing to species invasions and displacements, as well as the way that disturbances like drought, which will become more common in some regions under climate change, can rearrange communities by favoring some species over others.