Peter B. Moyle

Biological invasions: recommendations for U.S. policy and management.

The Ecological Society of America has evaluated current U.S. national policies and practices on biological invasions in light of current scientific knowledge. Invasions by harmful nonnative species are increasing in number and area affected; the damages to ecosystems, economic activity, and human welfare are accumulating. Without improved strategies based on recent scientific advances and increased investments to counter invasions, harm from invasive species is likely to accelerate. Federal leadership, with the cooperation of state and local governments, is required to increase the effectiveness of prevention of invasions, detect and respond quickly to new potentially harmful invasions, control and slow the spread of existing invasions, and provide a national center to ensure that these efforts are coordinated and cost effective. Specifically, the Ecological Society of America recommends that the federal government take the following six actions: (1) Use new information and practices to better manage commercial and other pathways to reduce the transport and release of potentially harmful species; (2) Adopt more quantitative procedures for risk analysis and apply them to every species proposed for importation into the country; (3) Use new cost-effective diagnostic technologies to increase active surveillance and sharing of information about invasive species so that responses to new invasions can be more rapid and effective; (4) Create new legal authority and provide emergency funding to support rapid responses to emerging invasions; (5) Provide funding and incentives for cost-effective programs to slow the spread of existing invasive species in order to protect still uninvaded ecosystems, social and industrial infrastructure, and human welfare; and (6) Establish a National Center for Invasive Species Management (under the existing National Invasive Species Council) to coordinate and lead improvements in federal, state, and international policies on invasive species. Recent scientific and technical advances provide a sound basis for more cost-effective national responses to invasive species. Greater investments in improved technology and management practices would be more than repaid by reduced damages from current and future invasive species. The Ecological Society of America is committed to assist all levels of government and provide scientific advice to improve all aspects of invasive-species management.

BIOLOGICAL INVASIONS OF FRESH WATER: EMPIRICAL RULES AND ASSEMBLY THEORY

Abstract Because the integrity of aquatic ecosystems is being challenged worldwide by invading species, there is a growing need to understand the invasion process and to predict the success and effects of invading species. Case histories of fish invasions in streams, lakes, and estuaries indicate that invading species and systems being invaded interact in idiosyncratic ways that are often hard to predict, largely because of the role of environmental variability in determining the outcomes of invasions. We nevertheless present a conceptual model of aquatic invasions and a dozen empirically-derived rules that seem to govern most aquatic invasions. While these rules are limited in their usefulness, they do seem to have more predictive value than rules derived from community assembly theory.

Stochasticity in structural and functional characteristics of an Indiana stream fish assemblage: a test of community theory.

In general, ecological assemblages and communities appear to be regulated primarily by either deterministic or stochastic processes. It is currently important to quantify the relative frequencies of these two types of assemblages since most ecological theory is applicable only to deterministic systems. We attempted to distinguish the mechanism regulating species abundances and trophic structure in an Indiana stream fish assemblage. Samples collected over a 12-yr period were separated by season (spring, summer, and autumn) and species were then assigned to a trophic group based on published dietary data. Analyses showed a total lack of persistence for the ranks of species abundances and the ranks of trophic groups for all seasons. Consequently, we conclude that this assemblage is probably regulated by stochastic factors. This finding is concordant with many other studies which have documented the substantial effects of environmental unpredictability (i.e., floods and droughts) on other stream taxocenes.

Biotic and Abiotic Controls in River and Stream Communities

Lotic ecologists share a major goal of explaining the distribution and abundance of biota in the worlds rivers and streams, and of predicting how this biota will respond to change in fluvial ecosystems. We discuss five areas of research that would contribute to our pursuit of this goal. For mechanistic understanding of lotic community dynamics, we need more information on: 1. Physical conditions impinging on lotic biota, measured on temporal and spatial scales relevant to the organisms. 2. Responses of lotic biota to discharge fluctuations, including the processes that mediate community recovery following resets caused by spates or droughts. 3. Movements of lotic organisms that mediate gene flow, resource tracking, and multilevel species interactions. 4. Life history patterns, with special emphasis on ontogenetic bottlenecks that determine the vulnerability of populations confronting environmental perturbation. 5. Consequences of species interactions for community- and ecosystem-level processes in rivers and streams. Without attempting to be comprehensive in our review, we discuss limits and limitations of our knowledge in these areas. We also suggest types of data and technological development that would advance our understanding. While we appreciate the value and need for empirical and comparative information, we advocate search for key mechanisms underlying community interactions as the crucial step toward developing general predictions of responses to environmental change. These mechanisms are likely to be complex, and elucidation of interacting bilateral, or multilateral, biotic and abiotic controls will progress only with the continuing synthesis of community- and ecosystem-level approaches in lotic ecology.

EFFECTS OF FLOW REGIME ON FISH ASSEMBLAGES IN A REGULATED CALIFORNIA STREAM

The fishes in Lower Putah Creek, a regulated stream in the Central Valley of California, were sampled over a 5-yr period, 1994-1998. Distinct fish assemblages were observed in the lower 37 km of stream using two-way indicator species analysis (TWIN- SPAN) and canonical correspondence analysis (CCA). The assemblages segregated in an upstream-to-downstream manner. Distinct differences were found between assemblages of native and nonnative fishes and their association with environmental variables and habitat use. Native fishes tended to cluster in areas with colder temperatures, lower conductivity, less pool habitat, faster streamflow, and more shaded stream surface. Numbers of nonnative fish were negatively correlated with increased streamflow, and numbers of native fish were positively correlated with increased flow. Hydrologic variability between years and seasons indicated that flow regime had a large effect on the fish assemblages. This study provides a clear demonstration of how native fishes in streams of the western United States exhibit different habitat requirements and respond to temporal variation in flow in a different manner than nonnative fishes. It supports the concept that restoration of natural flow regimes, in company with other restoration measures, is necessary if the continued downward decline of native fish populations in the western United States is to be reversed.

Regional Applications of an Index of Biotic Integrity for Use in Water Resource Management

Abstract The index of biotic integrity (IBI) integrates 12 measures of stream fish assemblages for assessing water resource quality. Initially developed and tested in the Midwest, the IBI recently was adapted for use in western Oregon, northeastern Colorado, New England, the Appalachians of West Virginia and Virginia, and northern California. The concept also was extended to Louisiana estuaries. In regions of low species richness, the IBI proved difficult to apply and often required extensive modification. Adapting the 1BI to those regions required that metrics be replaced, deleted, or added to accommodate regional differences in fish distribution and assemblage structure and function. Frequently replaced metrics include: proportion of individuals as green sunfish (Lepomis cyanellus), proportion of individuals as insectivorous cyprinids, proportion of individuals as hybrids, and number and identity of sunfish and darter species. The proportion of individuals as top carnivore metric was often deleted. Metr...

Persistence and Structure of the Fish Assemblage in a Small California Stream

The persistence and structure of a small but morphologically diverse fish assemblage of a California stream was examined to see if it had the characteristics of a deterministically regulated or stochastically regulated community. We evaluated persistence by monitoring the fish populations for 5 yr and examined resource use by measuring summer microhabitats and diets of each species. We also compared the microhabitats and diets of the juveniles and adults of each species to investigate the hypothesis that in stream fish assemblages at low diversity, juvenile fishes essentially function ecologically as separate species. Species composition in each of four stream sections was persistent over the 5—yr period, which included extreme flood conditions. Differences in species composition among sections reflected differences in their physical characteristics. The most abundant species were segregated by habitat, microhabitat, and/or diet. In addition, in all but one species, young—of—year were ecologically segrega...

Loss of Biodiversity in Aquatic Ecosystems: Evidence from Fish Faunas

Fishes are appropriate indicators of trends in aquatic biodiversity because their enormous variety reflects a wide range of environmental conditions. Fish also have a major impact on the distribution and abundance of other organisms in waters they inhabit. Examination of trends in freshwater fish faunas from different parts of the world indicate that most faunas are in serious decline and in need of immediate protection. Species most likely to be threatened with immediate extinction are either specialized for life in large rivers or are endemic species with very small distributions. We conservatively estimate that 20 percent of the freshwater fish species of the world (ca. 1800 species) are already extinct or in serious decline. Evidence for serious declines in marine fishes is limited largely to estuarine fishes, reflecting their dependence on freshwater inflows, or to fishes in inland seas. The proximate causes of fish species’ decline can be divided into five broad categories: (1) competition for water, (2) habitat alteration, (3) pollution, (4) introduction of exotic species, and (5) commercial exploitation. Although one or two principal causes of decline can be identified for each species, the decline is typically the result of multiple, cumulative, long-term effects. Ways to protect aquatic biodiversity include the implementation of landscape-level management strategies, the creation of aquatic preserves, and the restoration of degraded aquatic habitats. Without rapid adoption of such measures we are likely to experience an accelerated rate of extinctions in aquatic environments as human populations continue to expand.

Managing fire-prone forests in the western United States

The management of fire-prone forests is one of the most controversial natural resource issues in the US today, particularly in the west of the country. Although vegetation and wildlife in these forests are adapted to fire, the historical range of fire frequency and severity was huge. When fire regimes are altered by human activity, major effects on biodiversity and ecosystem function are unavoidable. We review the ecological science relevant to developing and implementing fire and fuel management policies for forests before, during, and after wildfires. Fire exclusion led to major deviations from historical variability in many dry, low-elevation forests, but not in other forests, such as those characterized by high severity fires recurring at intervals longer than the period of active fire exclusion. Restoration and management of fire-prone forests should be precautionary, allow or mimic natural fire regimes as much as possible, and generally avoid intensive practices such as post-fire logging and planting.

Invasion Resistance to Introduced Species by a Native Assemblage of California Stream Fishes

Assemblages of native stream fishes in California show a remarkable ability to resist invasion by introduced fishes as long as the streams are relatively undisturbed by human activity. Previous studies had indicated a high degree of spatial (microhabitat) segregation among the native fishes, which was confirmed by a principal components analysis of microhabitat use data from Deer Creek, a tributary of the Sacramento River. A null modelling study using the same data set was performed to see if competition was a major force structuring the assemblage, because theoretical studies had indicated that a competitively structured assemblage should be most able to resist invasions. The null models indicated that competition was not the major structuring force, so it is likely the assemblages are structured through a combination of morphological specialization (reflecting evolutionary history), predation, and some competition. The assemblages resist invasion through both environmental and biotic factors. Predation seems to be an especially important biotic factor.