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Life-History Strategies Predict Fish Invasions and Extirpations in the Colorado River Basin

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Life-History Strategies Predict Fish Invasions and Extirpations in the Colorado River Basin Ecological Monographs, 76(1), 2006, pp. 25±40 q 2006 by the Ecological Society of America LIFE-HISTORY STRATEGIES PREDICT FISH INVASIONS AND EXTIRPATIONS IN THE COLORADO RIVER BASIN JULIAN D. OLDEN,1,3 N. LEROY POFF,1 AND KEVIN R. BESTGEN2 1Graduate Degree Program in Ecology, Department of Biology, Colorado State University, Fort Collins, Colorado 80523 USA 2Larval Fish Laboratory, Department of Fishery and Wildlife Biology, Colorado State University, Fort Collins, Colorado 80523 USA Abstract. Understanding the mechanisms by which nonnative species successfully in- vade new regions and the consequences for native fauna is a pressing ecological issue, and one for which niche theory can play an important role. In this paper, we quantify a com- prehensive suite of morphological, behavioral, physiological, trophic, and life-history traits for the entire ®sh species pool in the Colorado River Basin to explore a number of hypotheses regarding linkages between human-induced environmental change, the creation and mod- i®cation of ecological niche opportunities, and subsequent invasion and extirpation of species over the past 150 years. Speci®cally, we use the ®sh life-history model of K. O. Winemiller and K. A. Rose to quantitatively evaluate how the rates of nonnative species spread and native species range contraction re¯ect the interplay between overlapping life- history strategies and an anthropogenically altered adaptive landscape. Our results reveal a number of intriguing ®ndings. First, nonnative species are located throughout the adaptive surface de®ned by the life-history attributes, and they surround the ecological niche volume represented by the native ®sh species pool. Second, native species that show the greatest distributional declines are separated into those exhibiting strong life-history overlap with nonnative species (evidence for biotic interactions) and those having a periodic strategy that is not well adapted to present-day modi®ed environmental conditions. Third, rapidly spreading nonnative ®shes generally occupy ``vacant'' niche positions in life-history space, which is associated either with ``niche opportunities'' provided by human-created envi- ronmental conditions (consistent with the environmental-resistance hypothesis of invasion) or with minimal overlap with native life-history strategies (consistent with the biotic- resistance hypothesis). This study is the ®rst to identify speci®c life-history strategies that are associated with extensive range reduction of native species and expansion of nonnative species, and it highlights the utility of using niche and life-history perspectives to evaluate different mechanisms that contribute to the patterns of ®sh invasions and extirpations in the American Southwest. Key words: attributes; endangered ®shes; functional diversity; functional niche; river regulation; traits; trilateral continuum. INTRODUCTION vasions based on environmental requirements (Peter- son 2003). Ecological niche theory posits that invasion Biological invasions are widely recognized as a sig- success will be mediated by intrinsic biological traits ni®cant component of human-caused environmental of species that dictate their degree of ``pre-adaptation'' change (Elton 1958) that often cause substantial eco- to habitats in the receiving ecosystem including biotic logical, evolutionary, and economic damage (Mack et interactions with resident native species. Despite some al. 2000, Pimental et al. 2000, Moritz 2002, Olden et recent claims that question the utility of the niche con- al. 2004). The ®eld of ecology has witnessed consid- cept in ecology (Hubbell 2001), contemporary ecolog- erable empirical and theoretical advances in forecasting ical niche theory can arguably be considered a very invasions (e.g., Kolar and Lodge 2001, but see Hulme powerful construct for understanding broad-scale pat- 2003), including the use of life-history traits as cor- terns and changes in the diversity, distribution, and relates of invasion success (Sakai et al. 2001) and niche abundance of species (see Chase and Leibold 2003). modeling for predicting the geography of species' in- The modern view of the ecological niche is an in- tegration of the original concepts proposed by Grinnell Manuscript received 25 February 2005; revised 31 May 2005; (1917) and Hutchinson (1957) and is pluralistically de- accepted 3 June 2005; ®nal version received 27 July 2005. Cor- ®ned as a combination of a species' ``place'' and responding Editor: K. O. Winemiller. 3 Present address: Center for Limnology, 680 Park Street ``role'' in the environment (Chase and Leibold 2003). N., University of Wisconsin±Madison, Madison, Wisconsin In this sense, an ecological niche de®nes where and 53706 USA. E-mail: [email protected] under what circumstances a species will exist and how 25 26 JULIAN D. OLDEN ET AL. Ecological Monographs Vol. 76, No. 1 it interacts with its environment. Life-history and eco- Comparative studies from a diverse array of ®shes logical trait attributes can be used to quantify a species' in freshwater and marine systems have independently ecological niche, which can be plotted in relation to identi®ed three primary life-history strategies that rep- other species in n-dimensional niche space where axes resent the endpoints of a triangular continuum arising are different traits (Rosenfeld 2002). Theoretically, the from trade-offs among the three basic demographic pa- signature of niche differentiation among species and rameters of survival, fecundity, and onset and duration between native and nonnative species' pools provides of reproduction (e.g., Winemiller 1989, Vila-Gispert et insight into the biotic and abiotic mechanisms respon- al. 2002, King and McFarlane 2003). In a comprehen- sible for long-term patterns of species' invasions and sive study, Winemiller and Rose (1992) examined 216 extinctions (Crawley et al. 1996). For example, the species (57 families) of North American freshwater and success of biological invasions may be determined by marine ®shes and provided the following descriptions potential ``niche opportunities,'' which arise when a of the characteristic biological and habitat environ- nonnative species possesses some set of traits that dif- mental attributes associated with each strategy: (i) pe- fer from those of native species and that are favored riodic strategists are large-bodied ®shes with late mat- by the environmental template (sensu Shea and Ch- uration, high fecundity per spawning event, low ju- esson 2002). Consequently, we would expect that the venile survivorship (i.e., no parental care), and that rate of spread of nonnative species will re¯ect the mag- typically inhabit seasonal, periodically suitable envi- nitude and extent of these opportunities (Sax and ronments; (ii) opportunistic strategists are small-bodied Brown 2000). The idea that ``niche opportunities'' can ®shes with early maturation, low fecundity per spawn- facilitate biological invasions has incited both excite- ing event, and low juvenile survivorship, and that typ- ment and disagreement among ecologists (Herbold and ically inhabit highly disturbed and unpredictable en- Moyle 1986); however, this hypothesis remains un- vironments; (iii) equilibrium strategists are small- to tested due to a lack of necessary species' trait infor- medium-bodied ®shes with moderate maturation age, mation and long-term empirical data. Niche theory is low fecundity per spawning event, and high juvenile also appealing in that it provides a basis for identifying survivorship (i.e., greater parental care), and that typ- possible mechanisms behind the range contractions of ically inhabit constant environments. The three primary native species in terms of niche overlap with both non- strategies of North American ®shes have some striking native species and ®t to the environmental template, similarities with earlier life-history models for animals both of which have changed dramatically in recent his- and plants (reviewed in Southwood 1988), but notably tory. In short, contemporary ecological niche theory the Winemiller and Rose model (hereafter called W± may provide a useful heuristic tool for understanding R model) extends the classic r±K model by splitting past and future distributional changes in native and the r strategy into the periodic and opportunistic strat- nonnative species, yet its potential remains largely un- egies and more narrowly de®nes the K strategy as the explored in quantitative terms. equilibrium strategy. A large number of biological traits across a diversity The life-history strategies of the W±R model can be of taxonomic groups have been used to describe a spe- interpreted as being adaptive with respect to the relative cies' ecological niche. For freshwater ®shes, attributes intensity and predictability of temporal and spatial var- related to morphology, behavior, life-history, and hab- iation in abiotic environmental conditions, food avail- itat and trophic requirements have proven very useful ability, and predation pressure (Winemiller 2005). This for relating species distributions to environmental var- model was envisioned to have strong implications for iables (e.g., Poff and Allan 1995, Lamouroux et al. understanding and predicting ®sh population responses 2002, Brazner et al. 2004). Of these attributes, life- to changing environments; however, it has only once history traits have been shown to be particularly good been applied in the literature for this purpose (i.e., predictors of both ®sh invasions (e.g., Fausch et al.
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