Michael P. Marchetti

Progress toward understanding the ecological impacts of nonnative species.

A predictive understanding of the ecological impacts of nonnative species has been slow to develop, owing largely to an apparent dearth of clearly defined hypotheses and the lack of a broad theoretical framework. The context dependency of impact has fueled the perception that meaningful generalizations are nonexistent. Here, we identified and reviewed 19 testable hypotheses that explain temporal and spatial variation in impact. Despite poor validation of most hypotheses to date, evidence suggests that each can explain at least some impacts in some situations. Several hypotheses are broad in scope (applying to plants and animals in virtually all contexts) and some of them, intriguingly, link processes of colonization and impact. Collectively, these hypotheses highlight the importance of the functional ecology of the nonnative species and the structure, diversity, and evolutionary experience of the recipient community as general determinants of impact; thus, they could provide the foundation for a theoretical framework for understanding and predicting impact. Further substantive progress toward this goal requires explicit consideration of within-taxon and across-taxa variation in the per capita effect of invaders, and analyses of complex interactions between invaders and their biotic and abiotic environments.

ALIEN FISHES IN CALIFORNIA WATERSHEDS: CHARACTERISTICS OF SUCCESSFUL AND FAILED INVADERS

The literature on alien animal invaders focuses largely on successful invasions over broad geographic scales and rarely examines failed invasions. As a result, it is difficult to make predictions about which species are likely to become successful invaders or which environments are likely to be most susceptible to invasion. To address these issues, we developed a data set on fish invasions in watersheds throughout California (USA) that includes failed introductions. Our data set includes information from three stages of the invasion process (establishment, spread, and integration). We define seven categorical predictor variables (trophic status, size of native range, parental care, maximum adult size, physiological tolerance, distance from nearest native source, and propagule pressure) and one continuous predictor variable (prior invasion success) for all introduced species. Using an information-theoretic approach we evaluate 45 separate hypotheses derived from the invasion literature over these three sta...

FISH INVASIONS IN CALIFORNIA WATERSHEDS: TESTING HYPOTHESES USING LANDSCAPE PATTERNS

An important goal of invasion biology is to identify physical and environ- mental characteristics that may make a region particularly receptive to invasions. The inland waters of California (USA) are highly invaded, particularly by fishes, although there is wide variation in numbers of nonnative fishes across the states watersheds. Here we examine patterns of fish invasions in California watersheds and their associations with natural en- vironmental characteristics, native fish diversity, and various measures of human habitat disturbance. Our analysis is based on an extensive data set on the distribution of freshwater fishes across Californias watersheds and on GIS land-use coverages for the entire state. We used canonical correspondence analysis to examine associations between environmental characteristics and the distributions of both native and nonnative fish species. We then employed an information-theoretic model-selection approach to rank hypothesized models derived from the fish invasion literature with regard to how well they predicted numbers of nonnative fishes in California watersheds. Our results indicate that pervasive, anthro- pogenic, landscape-level changes (particularly the extent of urban development, small-scale water diversions, aqueducts, and agriculture) influenced spatial patterns of invasion. In addition, we find that deliberately stocked fishes have different habitat associations, in- cluding a strong association with the presence of dams, than other introduced fishes. In our analysis, watersheds with the most native species also contain the most nonnative species. We find no evidence that existing watershed protection helps to prevent fish invasions in California, but we suggest that restoration of natural hydrologic processes may reduce invasion impacts.

Effects of Hatchery Rearing on Brain Structures of Rainbow Trout, Oncorhynchus mykiss

In this study, we contrast brain morphology from hatchery and wild reared stocks to examine the hypothesis that in salmonid fishes, captive rearing produces changes in brain development. Using rainbow trout, Oncorhynchus mykiss, as a model, we measured eight regions of the salmonid brain to examine differences between wild and hatchery reared fish. We find using multiple analysis of covariance (MANCOVA), analysis of covariance (ANCOVA) and discriminant function analysis (DFA) that the brains of hatchery reared fish are relatively smaller in several critical measures than their wild counterparts. Our work may suggest a mechanistic basis for the observed vulnerability of hatchery fish to predation and their general low survival upon release into the wild. Our results are the first to highlight the effects of hatchery rearing on changes in brain development inbreak fishes.

What's on the Menu? Evaluating a Food Availability Model with Young-of-the-Year Chinook Salmon in the Feather River, California

Abstract We adapted a salmonid food availability model by Rader to the Feather River in California and evaluated the ability of the model and two alternative measures of invertebrate abundance to predict the diet of young-of-the-year salmonids. We compared the stomach contents of 240 Chinook salmon Oncorhynchus tshawytscha with the model rankings and the taxonomic abundances in the benthos and drift. Raders model did not adapt well to the Feather River. The model was correlated with the stomach contents of Chinook salmon but not with invertebrate drift, as theorized by the models conceptual framework. Invertebrate abundance alone was a better indicator of salmonid feeding, and salmonid diet was correlated with both benthic and drift abundances. We urge caution in applying the model to novel regions and taxa without first examining the correlations between the drift and benthos. Observational studies of salmon foraging behavior, coupled with stomach content and invertebrate collections, may provide more ...

The conservation paradox of endangered and invasive species.

Conservation professionals are increasingly likely to encounter competing conservation priorities surrounding individual species, namely endangered species that also have non-native populations. This overlap arises when a non-native species is established in a novel location but is at the same time endangered within its native range. This creates a difficult philosophical paradox in which efforts to protect the endangered species conflict with the protection of the invaded ecosystem and its compliment of native taxa. Interest in the phenomenon arose from our work on Palea steindachneri (wattle-necked soft-shelled turtle) in Hawaii (Fig. 1). P. steindachneri is a large omnivorous freshwater turtle native to Vietnam and China (Ernst & Lovich 2009). In its home range it has been hunted close to extirpation largely due to its high cultural value as food and as a source of medicine. It is listed as endangered by the International Union for Conservation of Nature (IUCN) and threatened by the Convention on International Trade in Endangered Species (CITES). The Turtle Conservation Fund considers P. steindachneri one of the 48 most endangered turtle species on the planet (Bonin 2006). The few remaining wild populations of this turtle face uncertain survival prospects because the extreme rarity of the species has increased the cultural and market value of the remaining individuals (McKeown & Webb 1982). The cultural importance of the species led to its introduction by Chinese laborers to Mauritius, Hawaii, and the Sacramento River, California (Radford 2011), in the 1800s. The species is currently established on the Hawaiian island of Kauai, and there have been reports of individuals on nearby Oahu and Maui. These extralimital

Measuring the ecological impact of long-term flow disturbance on the macroinvertebrate community in a large Mediterranean climate river

The Feather River is a large flow-regulated river in the Central Valley of California. The Mediterranean climate of the area imposes a natural flow regime for the region that is characterized by predictable high flows in the winter and spring and low flows in the summer and fall. The Oroville Dam complex on the Feather River has created a permanent low-flow section of the river where a base flow is continuous year round but the natural annual variability of flow has been completely eliminated. We used this modified section of the river to examine the ecological impact that removing natural flow variability has on the macroinvertebrate assemblage and how we might measure such a change if it is present. Specifically, we examined whether biodiversity and community similarity differed between the low- and high-flow sections of the river for both benthic and drifting aquatic invertebrates. Using a modified Surber sampler we collected samples at three distinct time periods within a year (January, April, and July) for both drift and benthic fauna. Our results showed little difference between the low- and high-flow assemblages using common measures of diversity (i.e., species richness and Shannon diversity) and a measure of environmental tolerance (Hilsenhoff biotic index). Yet when we employed a multivariate measure of community similarity (i.e., non-metric multidimensional scaling) and associated statistical tests, we found significant assemblage differences between the low- and high-flow sections of the river. This study suggests that flow disturbance of this sort is likely to alter the macroinvertebrate community in ways that are not easily observed using common ecological metrics.

Non-indigenous fishes and their role in freshwater fish imperilment

The current state of freshwater biodiversity, and that of freshwater fishes in particular, can only be described as dismal (Dudgeon et al., 2oo6; Burkhead, 2012; Chapters r and 2). Freshwater extinction rates have been estimated to be around rooox above background extinction rates (Ricciardi & Rasmussen, 1999; Burkhead, 2012). Using North America as an example, a recent American Fisheries Society assessment indicates that 39% of North American freshwater fish taxa are imperilled: 230 are vulnerable, 190 are threatened, 280 are endangered and 6r are extinct or extirpated (Jelks et al., 2008). Global assessments paint the same general picture (www.iucn.org). What are the factors ultimately responsible for this situation? The objective of this chapter is to examine the role of non-indigenous fishes (hereafter NIF) in the decline and imperilment of native freshwater fishes. We provide a short primer to clarify a few key terms relating to invasion biology (Box 8.r). A biological invasion should not be viewed as an event, but rather a process comprised of several successive stages (Figure 8.r). The non-indigenous species introduction process begins with uptake of individuals, transport to a new area (transport outside of native range), and subsequently release into the wild (introduction to the wild) . These released individuals may then establish a self-sustaining population in the new area (establishment), and an established population may increase in abundance and expand its geographic range (spread) . Typically it is only when a species becomes abundant andfor widespread that it is

Impacts of aquatic invasive species and land use on stream food webs in Kaua’i, Hawai’i.

Anthropogenic disturbance is restructuring ecosystems and changing interactions within ecological communities. On the Hawaiʼian Islands, habitat degradation is linked to the establishment of invasive species; and together these stressors may lead to declining native populations and changes in food webs. In this study we employed stable isotopes to examine the structure of multiple Hawaiʼian stream food webs with varying levels of these stressors to illustrate interactions between native and non-native organisms that may represent drivers of community change. Limahuli stream contains all five species of native Hawaiʼian gobies, has a small number of introduced species, and minimal human disturbance. ʻOpaekaʼa, Hul¯eʼia and Kapaʼa streams are more heavily invaded than Limahuli and have greater human influence. We found increased species richness, increased trophic diversity, and increased total niche area in the more heavily invaded stream food webs relative to Limahuli. We also found non-native predatory species inhabiting top trophic positions in the three more heavily invaded streams and isotope mixing model estimates suggest that several species of non-natives have overlapping prey sources with native gobies in these sites. Lastly, we found that native stream organisms were nearly absent in ʻOpaekaʼa stream which also had the highest percent urban development of the streams sampled. Our results suggest significant trophic changes have occurred as the result of introduced species and possibly related to increased human disturbance.

Ecomorphological plasticity of juvenile fall-run chinook salmon (Oncorhynchus tshawytscha) in perennial and ephemeral streams

In the Central Valley of California, environmental characteristics differ between perennial and ephemeral stream types and therefore present different challenges for rearing salmonids with respect to water discharge, water temperature, food availability, and habitat complexity. Body shape of juvenile fall-run Chinook salmon (Oncorhynchus tshawytscha) reared in a perennial stream environment was compared to juveniles reared in an ephemeral stream environment. Using geometric morphometrics and multivariate analyses, this study presents morphological differences of rearing juvenile Chinook salmon both within and between ephemeral and perennial stream types. We found that shape differences between stream types were primarily associated with expansion of the mid-body region relative to differences in body length. Specifically, juvenile Chinook salmon reared in the ephemeral stream expressed increased body depth dominated by dorsal-ventral elongation of the dorsal, adipose, and anal fins. Eye position and gill opercula-body insertion points also were anteriorly shifted in the juvenile body shape of the ephemeral stream. Our findings support that juvenile Chinook salmon are morphologically flexible and can express habitat-specific developmental differences.