Spatial Scaling of Non-Native Fish Richness across the United States

<div><p>A major goal and challenge of invasion ecology is to describe and interpret spatial and temporal patterns of species invasions. Here, we examined fish invasion patterns at four spatially structured and hierarchically nested scales across the contiguous United States (i.e., from large to small: region, basin, watershed, and sub-watershed). All spatial relationships in both richness and fraction between species groups (e.g., natives vs. exotics) were positive at large scales. However, contrary to predictions using null/neutral models, the patterns at small scales were hump-shaped (unimodal), not simply negative. The fractions of both domestic (introduced among watersheds within the USA) and foreign (introduced from abroad) exotics increased with area across scales but decreased within each scale. The foreign exotics exhibited the highest dominance (lowest evenness) and spatial variation in distribution, followed by domestic exotics and natives, although on average natives still occupy larger areas than domestic and foreign exotics. The results provide new insight into patterns and mechanisms of fish species invasions at multiple spatial scales in the United States.</p></div

Appendix A. Hydrologic methods and classification.

Hydrologic methods and classification

Relationship between the fractions of both foreign and domestic exotic fish and surface area across multiple spatial scales.

<p>Foreign exotic fish accounted for a much lower overall exotic proportion than domestic exotic fish (The horizontal bars represent means across the four spatial scales). Note one sub-watershed from Florida with extremely high exotic fish richness is regarded as an outlier and then removed from the analysis.</p

Relationships between native and exotic richness (top), domestic and foreign exotic richness (middle), and domestic and foreign fraction (bottom) across multiple spatial scales in the contiguous United States.

<p>In each panel for sub-watersheds, the second order regression curves were based on quantiles of 0.1, 0.25, 0.5, 0.75, 0.9, and 0.95 from bottom to top, respectively; and the corresponding equations and significance were given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0097727#pone-0097727-t001" target="_blank">Table 1</a>. Exotic richness included both foreign and domestic exotics.</p

Environmental Drivers of Occupancy and Detection of Olympic Mudminnow

<p>The Olympic Mudminnow <i>Novumbra hubbsi</i> is a highly endemic freshwater fish found only in Washington State, where their distribution is limited to low-elevation wetland habitats. The distributional extent of the Olympic Mudminnow is well established, but local and watershed environmental features associated with their presence or absence within the range are poorly understood, making it difficult to determine habitat needs versus availability. We surveyed 22 sites in 2 years along the Chehalis River with the objective of modeling environmental characteristics associated with occupancy by Olympic Mudminnows, while also accounting for incomplete detection. Occupancy and detection probabilities were highly similar between years, and occupancy that incorporated detection probabilities was 47% higher than naive estimates in a given year. Modeling with environmental covariates supported the importance of low temperatures for predicting the occurrence of Olympic Mudminnows at sites, and detection within sites was associated most strongly with shallow depths and low dissolved oxygen. These results are consistent with prior research indicating the preferential use of groundwater springs by Olympic Mudminnows, particularly in warmer summer months. Our research expands the existing knowledge of Olympic Mudminnow distributions by documenting main-stem-oriented populations at varying levels of abundance and suggesting habitat features that may increase occupancy and detection probabilities. The sampling and modeling approach we describe also informs development of standardized survey protocols for Olympic Mudminnows, helping to optimize resources for monitoring occupancy and abundance across their limited range.</p

Location of milfoil presences (red filled circle) and absences (white empty circles) in lakes of Washington, USA, including King County (bottom right) containing 17 invaded lakes (filled squares) and 24 uninvaded lakes (empty squares).

<p>The city of Seattle, Washington (2010 population size of 608,660) is indicated as *.</p

Electronic Supplementary Material for Evidence for dispersal syndromes in freshwater fishes

Supplementary Figures S1-S6 and Tables S1-S

Appendix B. Life history and hydrologic metric relationships.

Life history and hydrologic metric relationships

Species rank curves for the three groups (natives, domestic exotics, and foreign exotics) using the distribution data at sub-watersheds level in the contiguous United States.

<p>Although foreign exotics still had smaller distribution than natives (but higher than domestic exotics; see inserted panel [mean ± SE]), the variation among species was much larger which was in agreement with the occupancy curves of the three species groups.</p

Stable isotopes characteristics of the fish species within their native and introduced ranges

Stable isotopes characteristics of the fish species within their native and introduced range