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Fish invasions in California watersheds: Testing hypotheses using landscape patterns
Ecological Applications
Abstract
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 state's 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 California's 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.
... Native freshwater fish communities are experiencing severe declines across the globe (Dudgeon et al., 2006;Moyle & Williams, 1990;Ricciardi & Rasmussen, 1999). Climate change (Moyle et al., 2013;Sharma et al., 2011Sharma et al., , 2019, fragmentation and regulation of rivers (Carlisle et al., 2010;Dynesius & Nilsson, 1994;Poff et al., 1997), pollution (Carpenter et al., 2011;Dudgeon et al., 2006), overharvest (Embke et al., 2019;Post et al., 2002), and invasive species (Marchetti, Light, et al., 2004;Marchetti et al., 2004b;Moyle & Marchetti, 2006) threaten freshwater ecosystems at all scales. Further, observed and predicted extinction rates are higher in aquatic than in terrestrial ecosystems, indicating that these environments are extremely sensitive to human activities (Moyle & Williams, 1990;Ricciardi & Rasmussen, 1999). ...
... Many of these approaches have strong potential for application to aquatic ecology (Er} os et al., 2020;Vasseur et al., 2014) but have rarely been used in this context. Expanded use of community ecology techniques, including stability approaches into highly invaded stream ecosystems could be useful (Bunn & Arthington, 2002;Marchetti, Light, et al., 2004;Marchetti et al., 2004b;Moyle & Marchetti, 2006). Stream restorations have long been criticized for lacking robust experimental designs and for tracking metrics that reflect the meaningful ecological change (Bernhardt et al., 2007). ...
... A return of predictable flow releases, and flow pulses during spring and fall are also important dynamics for native California fish as they cue spawning runs and allow juveniles habitat conditions that promote survivorship (Gasith & Resh, 1999;Moyle, 2002;Poff et al., 1997). In contrast, many nonnative species thrive in warm, deep, lacustrine waters and are often resilient in humanaltered environments (Marchetti, Light, et al., 2004;Marchetti et al., 2004b;Moyle & Marchetti, 2006). Many nonnative fish are nesting species that recruit best under stable hydrodynamic conditions (Moyle, 2002) such as those that occurred before the Accord. ...
Stream restorations are increasingly critical for managing and recovering freshwater biodiversity in human‐dominated landscapes. However, few studies have quantified how rehabilitative actions promulgate through aquatic communities over decades. Here, a long‐term dataset is analyzed for fish assemblage change, incorporating data pre‐ and post‐restoration periods, and testing the extent to which native assemblage stability has increased over time. In the late 1950s, a large capacity dam was installed on Putah Creek (Solano County, CA, USA), which altered the natural flow regime, channel structure, geomorphic processes, and overall ecological function. Notably, downstream flows were reduced (especially during summer months) resulting in an aquatic assemblage dominated by warm‐water nonnative species, while endemic native species subsisted at low levels as subordinates. A court‐mediated Accord was ratified in 2000, providing a more natural flow regime, specifically for native and anadromous fishes in the stream. The richness of nonnative species decreased at every site following the Accord, while the richness of native species increased or stayed constant. At the three most upstream sites, native species richness increased over time and ultimately exceeded nonnative richness. Native assemblage recovery was strongest upriver, closer to flow releases and habitat restoration activities, and decreased longitudinally downstream. Rank–abundance curves through time revealed that, while species evenness was low throughout the study, dominance shifted from nonnative to native species in the upstream sites coincident with rehabilitation efforts. Mean rank shifts decreased following flow rehabilitation; thus the assemblage became increasingly stable over time following flow rehabilitation. Putah Creek's rehabilitation may represent a model for others interested in improving endemic freshwater communities in degraded ecosystems.
... Akaike's Information Criterion (AIC) was used to assess support for different models using package MuMIn 61 . Models with a ∆ AIC of ≤ 2 were considered to have substantial support, while models with a ∆ AIC of ≤ 7 were considered to have some support 62 . Using the full set of models, Akaike importance weights for predictors were calculated as measures of parameter importance, by summing the Akaike weights for each model containing that variable 62,63 . ...
... Models with a ∆ AIC of ≤ 2 were considered to have substantial support, while models with a ∆ AIC of ≤ 7 were considered to have some support 62 . Using the full set of models, Akaike importance weights for predictors were calculated as measures of parameter importance, by summing the Akaike weights for each model containing that variable 62,63 . Parameters were classed as strongly supported by our models if they were significant in all strongly supported models (∆ AIC of ≤ 2) and had a cumulative Akaike weight of > 0.75 62 . ...
... Parameters were classed as strongly supported by our models if they were significant in all strongly supported models (∆ AIC of ≤ 2) and had a cumulative Akaike weight of > 0.75 62 . Parameters were considered somewhat supported if they were significant in any of the strongly supported models (∆ AIC of ≤ 2) regardless of Akaike weight 62 . ...
... It is thus not surprising that when flow regimes are altered, biodiversity is profoundly impacted (Bunn & Arthington, 2002). There are many examples of hydrological alteration driving community reassembly at local to regional scales via extirpation of native species and spread of non-natives (e.g., Light & Marchetti, 2007;Marchetti, Light, et al., 2004;Mims & Olden, 2013;Olden et al., 2006;Ruhi et al., 2016). However, it remains unknown whether fish invasion patterns are consistently associated with flow alteration at large spatial scales, across ranges of other anthropogenic drivers and environmental contexts. ...
... Given the extensiveness of flow modification in the USA (Carlisle et al., 2019;Poff et al., 2007;Zimmerman et al., 2018) and strong dependence of native fish species on natural flow variability (Bunn & Arthington, 2002;Mims & Olden, 2012), we hypothesized that flow regime alteration is at least as important as propagule pressure in controlling the composition of fish assemblages. Given that propagule pressure and flow regime alteration promote non-native species establishment and subsequent spread (Marchetti, Light, et al., 2004;Moyle & Light, 1996), we also expected that these two drivers of invasion would interact to accelerate freshwater fish invasions. ...
... Native assemblages appear in blue and nonnative assemblages in pink (translocated species) and red (exotic species). The boxplots in (a) can change the selection regime on fish assemblages, thus facilitating the establishment and success of invaders beyond regional scales (Marchetti, Light, et al., 2004;Moyle & Light, 1996;Olden et al., 2006;Ruhi et al., 2016). The results for opportunistic strategists (favoured in unpredictable environments) were less clear, because these were negatively associated with heightened flow variability and seasonality (albeit weakly). ...
Aim
River flow regimes are changing globally as a consequence of human use of freshwater resources. Additionally, rivers are among the most invaded ecosystems. Invasion biology predicts that the establishment and spread of non‐native species might be favoured both by new environmental regimes (niche opportunities) and by human‐mediated dispersal (propagule pressure). Here, we expand on past research by asking whether these two mechanisms act in isolation or whether they interact to facilitate the spread of non‐natives.
Location
Conterminous USA.
Time period
1987–2016.
Major taxa studied
Freshwater fishes.
Methods
First, we examined the geography of riverine fish invasions across 1,148 watersheds spanning the conterminous USA. We focused on species richness and the life‐history strategies of non‐native (both translocated and exotic) relative to native species pools. Second, we quantified flow regime alteration as the deviation between observed and expected contemporary flow regimes, using a combination of spectral analyses on long‐term discharge data and random forest models. We focused on two biologically relevant facets of the flow regime: flow variability and flow seasonality. We also estimated metrics of propagule pressure: recreational fishing pressure and socioeconomic activity. We then compared the strength of evidence associating riverine fish invasions with flow alteration, propagule pressure, and interactions between the two mechanisms.
Results
We found that alteration of flow variability and seasonality is widespread across the conterminous U.S. rivers, and has favoured invasions by filtering specific life‐history strategies. Importantly, high levels of flow stabilization and propagule pressure interacted: where co‐occurring, these two drivers were associated with higher fish invadedness levels than expected based on their individual effects.
Main conclusions
Our results underscore the need to consider different drivers of invasion concurrently. Otherwise, important synergistic interactions might be missed that could explain (and guide management strategies to mitigate) the high levels of invasion in fresh waters.
... Recently, some efforts have been devoted to analyze the roles of habitat degradation and invasive species in the decline and extinction of native species for different taxonomic groups, with contradictory conclusions (e.g., Marchetti et al. 2004, MacDougall and Turkington, 2005, Light and Marchetti 2006. Light and Marchetti (2006) tested the role of invasive freshwater fish species and habitat degradation in the decline of native fish assemblages in Californian streams, while MacDougall and Turkington (2005) used experimental designs to check the same hypothesis on plant assemblages in an oak savannah in Canada. ...
... We first evaluated if invasive species were acting as ''drivers' ' (Fig. 1B) or ''passengers'' (Fig. 1C) in the process of native fish biodiversity loss led by other factors, such as habitat degradation, at the reach scale. This work is a refinement of previous work carried out by Marchetti et al. (2004) and Light and Marchetti (2006) on freshwater fish assemblages at coarser spatial scales. We then evaluated the effect of habitat degradation in the relationship between invasive fish species and native assemblages, testing whether native species simply responded to the abundance of invasive species or if habitat degradation modified the functional relationships between natives and invasives (Fig. 1D). ...
... Colonisation by invasive species is one of the most important threats to biodiversity at a global scale (Sala et al. 2000;Mora and Sale 2011) and, in most parts of the world, is considered to be the single most important threat to freshwater biodiversity and ecological function (Lodge et al. 2000). Modified waterbodies are potentially more susceptible to invasive species (Moyle 1976;Marchetti et al. 2004), primarily because of their links to human activities including intentional or accidental introduction of non-native species by humans (Chapple et al. 2012) and the presence of exotic species can be used as an indicator of degraded conditions (Kennard et al. 2005). ...
... Although not all non-native species become invasive (Williamson 1989), they can impact native biodiversity directly or indirectly (De Silva et al. 2009). Established non-native species can frequently outcompete native species in terms of environmental tolerance (Marchetti et al. 2004;Canonico et al. 2005), breeding success (Pompei et al. 2016), predation (Brown and Moyle 1991;McDowall 2006), resource acquisition and body size (Lowery and Holdich 1988;Mack et al. 2000;Bubb et al. 2006). However, there are similarly examples of non-native species that have minimal apparent impacts on native biota (Thomas and Palmer 2015). ...
Invasion by armoured catfishes (Loricariidae) is a threat to native fish communities of warm, freshwater habitats. Following importation as an ornamental species, the vermiculated sailfin catfish Pterygoplichthys disjunctivus, has become established in inland waters of Bangladesh. We recorded the distribution of sailfin catfish in Bangladesh. Vermiculated sailfin catfish was recorded in 17 rivers across the majority of the country, with well-established breeding populations in four localities. We measured competition between three native carps and sailfin catfish by determining growth and survival, and by carrying out gut analysis. The competition experiment was carried out using a randomised block design in earthen ponds with similar physico-chemical parameters to freshwater habitats in Bangladesh. It demonstrated that growth and survival rate of native cyprinid fishes can be adversely impacted in the presence of sailfin catfish. In high-density catfish treatments, growth of Cirrhinus cirrhosus (bottom-feeding omnivore), Labeo rohita (midwater omnivore) and Catla catla (pelagic planktivore) was reduced by 48.4%, 21.4% and 2.4% respectively, compared to controls containing the three cyprinids but no catfish. Survival of C. cirrhosus reduced to 70% in high-density catfish treatments, compared to 100% in catfish-free ponds, with lesser effects on the other species. Low- and medium-density catfish treatments generated lesser growth and survival effects. Catfish diet remained stable across density treatments, but diet of native fishes deviated increasingly from control values as catfish density increased. This study demonstrates impacts of sailfin catfish on native fish species and the increasing distribution of sailfin catfish in Bangladesh.
... Traits associated with the spread and impact of nonnative species have rarely been studied, except in predictive and profiling studies, which means that assumptions about the underlying mechanisms remain unresolved and speculative (Kolar & Lodge 2002;Marchetti et al. 2004aMarchetti et al. , 2004bMoyle & Marchetti 2006;Ribeiro et al. 2008). In general, the successful spread and impact of species seem to depend on their broad physiological tolerance and origin from a nearby region; this highlights the importance of preadaptation to invaded ecosystems. ...
... Aquatic ecosystems that are heavily or frequently disturbed by humans therefore seem to be highly susceptible to invasions. For example, dam density and reservoir area, which are related to the alteration, destruction, and fragmentation of freshwater habitats, as well as to hydrological changes (Leprieur et al. 2008, Clavero et al. 2013, are positively associated with the number of nonnative aquatic species (Marchetti et al. 2004a, Clavero et al. 2013, Su et al. 2021. Artificially created habitats such as water impoundments may also facilitate invasions, because they are more accessible to humans than natural lakes and also because they reduce the distance between invaded and noninvaded areas, thus increasing the likelihood that natural lakes will in turn be invaded ( Johnson et al. 2008). ...
Freshwater fish have been widely introduced worldwide, and freshwater ecosystems are among those most affected by biological invasions. Consequently, freshwater fish invasions are one of the most documented invasions among animal taxa, with much information available about invasive species, their characteristics, invaded regions, invasion pathways, impacts, and management. While existing reviews address specific aspects of freshwater fish invasions, there is still a gaping lack of comprehensive assessments of freshwater fish invasions that simultaneously address pivotal and connected elements of the invasion process. Here, we provide a holistic review, together with quantitative assessments, divided into four major parts: ( a) introduction pathways, ( b) characteristics of nonnative species and invaded ecosystems that explain successful invasion processes, ( c) invasion impacts and their mechanisms, and ( d) management. We highlight data gaps and biases in the current databases and highlight a basic lack of understanding of several aspects of freshwater fish invasions. In addition, we provide recommendations for future studies.
Expected final online publication date for the Annual Review of Ecology, Evolution, and Systematics, Volume 53 is November 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... Traits associated with the spread and impact of nonnative species have rarely been studied, except in predictive and profiling studies, which means that assumptions about the underlying mechanisms remain unresolved and speculative (Kolar & Lodge 2002;Marchetti et al. 2004aMarchetti et al. , 2004bMoyle & Marchetti 2006;Ribeiro et al. 2008). In general, the successful spread and impact of species seem to depend on their broad physiological tolerance and origin from a nearby region; this highlights the importance of preadaptation to invaded ecosystems. ...
... Aquatic ecosystems that are heavily or frequently disturbed by humans therefore seem to be highly susceptible to invasions. For example, dam density and reservoir area, which are related to the alteration, destruction, and fragmentation of freshwater habitats, as well as to hydrological changes (Leprieur et al. 2008, Clavero et al. 2013, are positively associated with the number of nonnative aquatic species (Marchetti et al. 2004a, Clavero et al. 2013, Su et al. 2021. Artificially created habitats such as water impoundments may also facilitate invasions, because they are more accessible to humans than natural lakes and also because they reduce the distance between invaded and noninvaded areas, thus increasing the likelihood that natural lakes will in turn be invaded ( Johnson et al. 2008). ...
Freshwater fish have been widely introduced worldwide, and freshwater ecosystems are among the most affected by biological invasions. Consequently, freshwater fish invasions are one of the most documented invasions among animal taxa, with much information available about invasive species, their characteristics, invaded regions, invasion pathways, impacts, and management. While existing reviews address specific aspects of freshwater fish invasions, there is still a gaping lack of comprehensive assessments of freshwater fish invasions that simultaneously address pivotal and connected elements of the invasion process. Here, we provide a holistic review, together with quantitative assessments, divided into four major parts: (1) introduction pathways; (2) characteristics of non-native species and invaded ecosystems to explain successful invasion processes; (3) invasion impacts and their mechanisms; and (4) management. We highlight data gaps and bias in current databases and point to the basic lack of understanding of several aspects of freshwater fish invasions. Finally, we provide recommendations for future studies.
... Stabilization of aquatic habitat that reduces disturbance by natural flood-drought cycles can lead to invasions by the non-native species described above because most require slow moving, permanent water for survival (Meffe, 1984;Moyle and Light, 1996;Gasith and Resh, 1999;Adams, 2000;Marchetti et al., 2004c). In contrast, native species in the region have evolved traits for coping with ephemeral habitat or promoting resilience once hydrologic stress has subsided. ...
... Eradicating all non-native aquatic species is not feasible; however, managing a single ecosystem engineer in this case could have broad-ranging, trickle-down effects on the richness and abundance of invasive species because niche opportunities would diminish or perhaps even be eliminated for some areas (Crooks, 2002;Strayer, 2012). At the same time, hydrologic conditions may revert to more punctuated, flashy dynamics that repress the dominance of the most insidious invaders while tipping the scales back in favor of natives (Stromberg, 2001;Marchetti et al., 2004c). ...
We discuss the problems associated with beaver disturbance and its effects on conserving the region's native fauna and flora. We refute arguments underlying the claim that beaver is native to the region, and review paleontological, zooarchaeological, and historical survey data from renowned field biologists and naturalists over the past ~160 years to show that no evidence exists that beaver arrived by any means other than deliberate human introduction.
... In addition, the relationships among biotic degradation (here the abundance of non-natives fishes), land use, and local scale habitat alteration were relatively weak, but significant in both streams and rivers, with the exception of the relationship between land use and biotic degradation in rivers, which proved to be insignificant. Former studies show that the abundance of nonnative fishes is mostly related to the distribution of fish ponds and water reservoirs in this and in other ecoregions (Marchetti et al., 2004;Hermoso et al., 2011;Erős et al., 2012). These landscape level alterations may also influence the local stream environment and facilitate the spread of non-natives species (Marchetti et al., 2004;Hermoso et al., 2011;Takács et al., 2017). ...
... Former studies show that the abundance of nonnative fishes is mostly related to the distribution of fish ponds and water reservoirs in this and in other ecoregions (Marchetti et al., 2004;Hermoso et al., 2011;Erős et al., 2012). These landscape level alterations may also influence the local stream environment and facilitate the spread of non-natives species (Marchetti et al., 2004;Hermoso et al., 2011;Takács et al., 2017). Since fish ponds and reservoirs are more common in streams than in rivers in this ecoregion, it is not surprising that we found stronger coupling between biotic degradation and landscape and local scale habitat alteration in streams than in rivers. ...
We examined the effects of regional scale land use and local scale environmental and biotic stressors on alpha, beta and zeta diversities of native fish communities in wadeable streams and non-wadeable rivers in the Danube basin, Hungary. Relationships among land use and local scale environmental and biotic stressors were weak both in streams and rivers, suggesting that these stressors act relatively independently. Alpha diversity decreased strongly with increasing local scale environmental stressor intensity in rivers. On the contrary, its response to stressors was more obscure in streams, where the best-fit statistical model indicated the importance of the interaction between land use, local scale environmental and biotic stressors, while the secondly ranked model highlighted the negative impact of local scale environmental stressors. Analysis of variance using distance matrices provided evidence that stressors alone and in interactions explained compositional differences of pairs of study sites (beta diversity). Considering the degree of overall degradation, both local (alpha) and among-site (beta and zeta) diversity indices responded to increasing stressor intensity, generally negatively. Riverine fish communities showed higher degrees of similarity (lower beta and higher zeta) than stream fish communities. They also showed increasing similarity (i.e. homogenization) with increasing overall stressor intensity, unlike stream fish communities, which showed no relationship with overall stressor intensity. Our results suggest that the relationships between land use and local scale environmental and biotic stressors can be complex and so do their effects on biodiversity. While stressor specific indices can provide information on the role of specific stressors in some cases, the examination of overall stressor effects is needed to assess realistically the effects of anthropogenic disturbances on native fish diversity. Diversity indices that quantify among-site changes in species composition, such as measures of beta and zeta diversity, can be fruitful for better understanding the role of multiple stressors in structuring ecological communities.
... However, food resources impact population fitness and define the permanence of nonnative species (Zambrano et al. 2010). Furthermore, the spatial and temporal variability promoted by human activities (e.g., construction of dams) favors non-native species with higher tolerances to changes in physicochemical characteristics and plasticity in life history traits (Marchetti et al. 2004;Gozlan et al. 2010). ...
... Among the goals of biological invasion studies are predicting those environments most susceptible to invasion, defining species that will become invasive, and identifying factors that facilitate establishment (Marchetti et al. 2004;Fleming and Dibble 2015). Several factors are associated with the invasion success of a species. ...
The Paranapanema River is most frequently invaded by non-native fish from the Upper Paraná River Freshwater Ecoregion. To understand how the diet of non-native fishes varies based on habitat type, we studied 12 populations of 6 non-native fish species with the aim of verifying whether diet, niche breadth, or trophic guild vary between lentic and lotic habitats. Fish were sampled in both habitats in the Paranapanema River basin between August 2014 and March 2016. A permutational multivariate analysis of variance-PERMANOVA was applied so that the composition of fish diet could be compared between habitats. Levin's standardized index was used to evaluate the trophic niche breadth of the species, revealing differences in the diets of Ossancora eigenmanni, Auchenipterus osteomystax and Trachelyopterus galeatus based on habitats. Seven trophic guilds were identified, and those for Serrasalmus marginatus, Loricariichthys platymetopon, and T. galeatus were the same (piscivores, detritivores, and omnivores, respectively) in both habitats. In contrast, the trophic guilds of O. eigenmanni, A. osteomystax, and Plagioscion squamosissimus varied between the habitats. Habitat-specific variability in the diet composition of the species and, for the most, the niche breadth in the lotic habitats increased; therefore, we conclude that this type of environment can provide access to a greater variety of food resources for non-native fishes.
... Black fish indicate the native range before introduction. status definitions include US state boundaries (Rahel 2000), watersheds associated with particular US states (e.g., Gido, Schaefer, and Pigg 2004;Marchetti et al. 2004;McKinney 2005;Kirk, Maitland, and Rahel 2020), "drainages" (Gido and Brown 1999), "river basins" (e.g., Olden, Kennard, and Pusey 2008;Liu et al. 2017;Sommerwerk et al. 2017;Tedesco et al. 2017), and our provincial (HUC8) definition. Studies using these narrower definitions of native status have contributed to our understanding of invasion patterns (Davis and Darling 2017;Anas and Mandrak 2021;Qian et al. 2023), drivers of nonnative richness (Guo and Olden 2014;Peoples et al. 2018), and biological homogenisation (Kirk, Maitland, and Rahel 2020;Peoples et al. 2020;Sleezer et al. 2021). ...
Scale‐Dependency of Native Status: Classifying populations as native or nonnative requires well‐defined range boundaries for species. While many studies define native status according to large biogeographic realms, natural dispersal barriers often limit species distributions at regional or smaller spatial extents. As such, native/nonnative definitions are inherently scale‐dependent and estimates of community invadedness thus depend on the spatial resolution at which native status is defined. For example, nonnative species can be introduced among realms, among regions within realms, and among ecological provinces within regions (hereafter, simply “provinces”). By explicitly considering the scale‐dependency of native/nonnative status definitions, we can more effectively compare results across studies, more comprehensively evaluate the degree of invasion levels, and more objectively communicate the native status of a species.
Location: 30,034 stream segments, conterminous United States.
Time Period: 2000–2023.
Major Taxa Studied: Freshwater fishes.
Quantifying Fish Community Invadedness Across US Streams:
We illustrate the importance of scale‐dependent native status definitions by quantifying nonnative species richness and relative abundance in stream fish communities across the United States, finding that provincially nonnative species are nearly four times as prevalent as extra‐realm nonnative species, and represented approximately 10% of all individuals in average community surveys.
Implications: Unrealistically broad native status definitions underestimate community invadedness. Dismissing regionally and provincially nonnative species can have severe ecological consequences, including displacement and hybridisation with native species and the loss of unique communities through biotic homogenisation. These consequences may undermine efforts to maintain and protect distinct local biodiversity and conserve endemic species.
... Numerous invasive species exhibit high rates of reproduction, which facilitates population establishment in new areas (Simberloff et al., 2013). Many invasive species quickly reach maturity and exhibit faster growth than native species, providing them with a competitive edge in resource acquisition (Marchetti et al., 2004). Invasive organisms can survive in various habitats and outcompete with native species by adapting to a broad range of environmental conditions. ...
Zoology: Advancements and Research Trends is a comprehensive compilation of cutting-edge research and insights in the field of Zoology. This book has been meticulously curated to serve as an invaluable resource for students, researchers, and professionals who are keen to explore the latest advancements and emerging trends in various sub-disciplines of Zoology, including toxicology, pharmacology, and general zoology. As an Assistant Professor in the Department of Zoology, Wildlife, and Fisheries at the University of Agriculture, Faisalabad, I, Dr. Muhammad Umar Ijaz, have dedicated over a decade to advancing our understanding of animal physiology, cell biology, toxicology and pharmacology. My extensive experience in these fields, coupled with my broader expertise in general zoology, has provided me with a profound appreciation for the complex interplay between living organisms and their environments. This book reflects my commitment to bringing together a diverse array of topics that highlight the breadth and depth of contemporary zoological research. Zoology: Advancements and Research Trends is not just a collection of research topics but a reflection of the collaborative spirit that drives scientific progress. The diverse expertise of the contributing authors ensures that this book offers a well-rounded perspective on the current trends and future directions in Zoology. I hope that this book will serve as a valuable reference for those in academia and industry, providing insights that will inspire future research and contribute to the ongoing dialogue in the field. It is my sincere belief that the knowledge shared within these pages will help shape the future of Zoology, ultimately contributing to the betterment of our understanding and stewardship of the natural world. I would like to express my gratitude to all the contributors, reviewers, and colleagues whose efforts have made this book possible. I also extend my thanks to the students and researchers who continue to push the boundaries of what we know and what we can achieve in this dynamic field.
... Our results challenge the prevailing notion that disturbance invariably promotes invasion. While disturbance can create opportunities for invasive species by disrupting established communities and increasing resource availability (Lockwood et al., 2007), it can also act as a stressor that limits population growth and increases extinction risk (Catford et al., 2012;Gerhardt & Collinge, 2003;Hobbs & Huenneke, 1992;Lake & Leishman, 2004;Marchetti et al., 2004;Minchinton, 2002;With, 2004). However, there is an alternative hypothesis, the passenger model, that posits that disturbance has no effect on the invasive population (MacDougall & Turkington, 2005). ...
Understanding the response of species to global change requires disentangling the drivers of their distributions across landscapes. Colonization and extinction processes, shaped by the interplay of landscape‐level and local patch‐level factors, are key determinants of these distributions. However, disentangling the influence of these factors, when larger‐scale processes manifest at local scales, remains a challenge. We addressed this challenge by investigating the colonization and extinction dynamics of the aquatic plant, Hydrilla verticillata, in a complex riverine rock pool system. This system, with hundreds of rock pools experiencing varying flooding frequencies, provided a natural laboratory to examine how a single landscape‐level disturbance can differentially impact colonization and extinction depending on local patch characteristics to shape species distributions. Using 5 years of data across over 500 sites and more than 5000 surveys, we employed dynamic occupancy models to model colonization, extinction, and changes in Hydrilla patch occupancy while accounting for imperfect detection. Our results revealed that larger, infrequently flooded pools closer to the river were more likely to be colonized. In contrast, local extinction of Hydrilla was more likely in smaller pools closer to the river that flooded frequently. These findings underscore the importance of considering context‐dependence in species distribution models. The same landscape‐level disturbance (flooding) had opposing effects on colonization and extinction, with the direction and magnitude of these effects varying with local patch characteristics. Our study highlights the need for integrating local and landscape‐level factors, and considering how larger‐scale processes play out at the patch level, to understand the complex dynamics that shape species distributions.
... The potential for the establishment of NIS is strongly influenced by environmental factors also, [48,49,50] and is often associated with disturbances [51,52]. Degraded water quality, for example, plays an important role in the establishment of NIS in aquatic ecosystems. ...
The present study assessed and compared the diet and trophic positions (TP) of two carnivorous fish H. macrolepidota and C. ocellaris from Chenderoh Reservoir, Malaysia. The focal goal of the study was to understand the effects of invasive non-indigenous species (NIS), C. ocellaris, on the native indigenous (IS) fish species, H. macrolepidota. Data were acquired from September 2014 to February 2015 within the study area. The assessment was grounded in stomach content analysis (SCA) and stable isotope analysis (SIA), which collectively clarified the feeding habits and trophic positions (TP) of these selected fish. In total, 184 fish samples (comprising 64 individuals of H. macrolepidota and 120 individuals of C. ocellaris) underwent stomach content analysis (SCA). Additionally, 24 individuals (12 of H. macrolepidota and 12 of C. ocellaris), sampled from December 2014 to February 2015, were selected for stable isotope analysis (SIA). The mean RGL values for H. macrolepidota and C ocellaris were 0.98 ± 0.18 and 1.10 ± 0.15 (Mean ± SD), respectively, aligning with known ranges for carnivorous fish. These values also clarified that both species occupy higher TP in the food web as tertiary or quaternary consumers. SCA findings also revealed that fish and crustaceans were the predominant food categories for H. macrolepidota, while C. ocellaris predominantly fed on fish. The mean stomach fullness index (MSF) and the gastrosomatic index (GSI) corroborated the differences in the foraging performance of the fishes, with C. ocellaris having a higher MSF (2.03) compared to H. macrolepidota (0.65). These implied that C. ocellaris had plentiful of food and encountered fewer diet-related challenges in the ecosystem. From SIA, δ13C values indicated that the primary carbon sources for both species are C3 plants, particularly aquatic vegetation. Further, δ15N values further ensured that both H. macrolepidota and C. ocellaris are carnivorous in nature and occupy higher TP in the ecosystem.
... The effects of altered hydrology and watershed disturbance on reservoirs may make them more susceptible to nonnative fish invasions (Marchetti et al. 2004;Havel et al. 2005). White perch are a common freshwater invader (Hergenrader and Bliss 1971;Boileau 1985;Prout et al. 1990;Mills et al. 1994;Feiner et al. 2012) and produce viable populations outside of their native range due to favorable life history traits that include reproductive flexibility (Sheri and Power 1968;Feiner et al. 2012) and opportunistic feeding (Reid 1972;Couture and Watzin 2008). ...
Managing impounded river systems is a recurring challenge for aquatic resource professionals because reservoirs serve multiple functions with different ecological and socioeconomic outcomes. However, research on fishes in reservoirs has disproportionally focused on recreationally and economically important species, with less attention directed toward fish assemblages despite the potential for management at the assemblage level. As such, evaluation of relationships between reservoir fish assemblages and biotic and abiotic factors and testing whether assemblage structure is affected by changing environmental conditions may deepen ecological understanding and provide insights for reservoir fisheries management. Our overall objective was to assess these relationships in 11 reservoirs from North Carolina, USA. We sampled fish assemblages in the reservoirs, which spanned five river basins representing a range of habitat conditions, using experimental gillnets and pulsed DC nighttime electrofishing. Multivariate statistical analyses indicated that taxonomic differences in fish assemblage composition among river basins followed a gradient of productivity. The top contributing species to reservoir dissimilarity were bluegill (Lepomis macrochirus), gizzard shad (Dorosoma cepedianum), black crappie (Pomoxis nigromaculatus), and white perch (Morone americana). These four species were positively associated with factors that reflect increasing eutrophic conditions in the 11 reservoirs and could, therefore, serve as indicators of reservoir productivity, anthropogenic influence, and fish assemblage structure, in addition to their key role in reservoir fisheries management. Whereas fisheries research has historically focused on assessing fish populations, our results illustrate the ecological and management insights derived from simultaneously collecting assemblage- and population-level data. Research on reservoir fish assemblages in relation to biotic and abiotic conditions may help advance fish ecology and management alike.
... Human activities have also resulted in spatial and temporal variability, which gives rise to invasive species that adapt well to physicochemical changes and possess high plasticity in their life-history traits [1,16]. The ability to adapt rapidly to new conditions is one characteristic of successful invaders and these species have a flexible life history [1]. ...
Despite the widespread occurrences of development plasticity in non-native populations, its underlying causes and consequences for species fitness remain unclear. This study aims to assess the potential invasion characteristics of Gambusia holbrooki in different habitats (lotic vs. lentic) of an island ecosystem (Gökçeada, Turkey), by using metrics related to growth and diet. Fish specimens were collected by electro-fishing quarterly between September 2019 and July 2020 in Büyük Stream and the shorelines of the Uğurlu Reservoir. The growth metrics of the species were similar in both habitats, showing positive allometry (b > 3) and high condition (K > 2). The vacuity index (VI), showing low values for each habitat (12.7 in lotic vs. 19.3 in lentic), was a mark of high feeding density of the species. Aquatic insects and zooplankton were the main food items in the diet of this invasive fish, and it exhibited generalist feeding habits with specifics depending on the habitats. Because the species fed heavily on Diptera in the lotic habitat and Cladocera in the lentic habitat, niche breadth values were low (0.16–0.22). It was determined that different habitat types did not have an effect on the LWR and condition of G. holbrooki, but changed its feeding strategy. Positive allometric growth and good condition, a comprehensive food range, high levels of feeding density, and high nutritional plasticity can be considered essential parameters in explaining the invasion success of this fish species living in two different habitat types.
... water quality, substrate composition and flow regime) have been considered as important predictors of ecosystem invasibility (Lapointe et al. 2012;Marchetti et al. 2004;Murphy et al. 2015). We have shown that temperature and climate in general (Study 1) and water flow (Study 3) influence the invasive success of mosquitofish. ...
Biological invasions are currently a huge, global environmental issue in freshwater ecosystems. The mosquitofishes Gambusia holbrooki and G. affinis are freshwater poeciliid fishes native to North America that have been introduced worldwide since the early 1900s and are among the world’s most invasive fish. They were regarded as three separate species and later as two subspecies of a single species before a genetic study in 1988, so their distribution is unclear. This thesis aims to contribute to the understanding of the invasive success of these two invasive fishes. We reviewed four Internet databases and the literature to clarify their introduction history and geographical distribution, establish their introduction routes, and analyse predictors of their invasive success. The four databases reviewed contain many clear errors and we estimate that G. holbrooki has established in ca. 49 countries and G. affinis in 44. For predicting introduction probability and establishment success of mosquitofish, the best explanatory variables among those available were related to climate, such as mean temperature or latitude, whereas for the probability of donating mosquitofish, economic drivers such as the intensity of exports and gross domestic product per capita were more important. A meta-analysis of the published evidence of ecological impacts of mosquitofishes shows a number of points, namely that the overall impact is: i) similar for the two species; ii) clear and strong for fish, macroinvertebrates, amphibians, and some zooplanktonic groups (such as copepods and rotifers) and more variable for taxa at lower trophic levels and for ecosystem features; iii) general for the number of aggressive acts received and decreases in density and biomass but more variable for other response variables such as size structure, life history traits, or other behavioural traits; and iv) highly heterogeneous and context-dependent on a number of features such as the target species involved, the experimental setting (depth of the study system, density of fish used), and environmental factors such as temperature. We estimated
-1
the mean critical swimming speed (Ucrit) of G. holbrooki as 14.11 cm s
22.26), which is lower than for many other fish of similar size and confirms that this species is limnophilic and its invasive success might be partially explained by hydrologic alteration. However, we demonstrate that Ucrit and maximal metabolic rate vary markedly with fish size and sex, with males having much higher values for the same weight, and thus probably being more resistant to strong water flows.
... s0135 Altered disturbance regimes will affect invasion p0210 Another particularly important aspect of changing disturbance regimes will be the consequences for invasion and invaders. In some cases, natural disturbance regimes keep invaders at bay, effectively creating natural invader-free space (Boddy and McIntosh, 2021), whilst in others, disturbances, especially human driven ones, facilitate invasion (Marchetti et al., 2004). Thus, changes in the disturbance regimes experienced by freshwater systems are very likely to influence invasion and associated consequences, indicating that better understanding of these controls is needed. ...
Aim: We outline a general framework for understanding the dimensions of freshwater disturbances, and highlight their consequences covering individual, population, and community-level effects.
Main concepts covered: We distinguish between disturbance drivers and disturbance impacts in a general definition of disturbance, and emphasize the roles of resistance and resilience in determining disturbance impacts. We highlight influences on individuals, life histories and populations, and illustrate how they are dominated by a trade-off between growth and development versus disturbance mortality risk, and the effects of disturbance predictability on solving that trade-off. The difference between refuges, which are important for population recovery on ecological timescales, is distinguished from evolutionary refugia, which are important over much longer time scales (i.e., millennia). The profound influences of freshwater disturbances on the species richness and traits of freshwater communities are described, including their links to disturbance-impacts on the food resources of consumers. When considering community assembly, we outline how species sorting mechanisms may be particularly important following disturbance, whereas disturbance predictability is linked to the turnover of species between habitats. Finally, in examining influences on food webs, disturbance, by altering the composition of consumers, adjusts bottom-up energy flow to predators, the potential for top-down control in food webs, and the length of food chains.
Conclusion/outlook: We suggest climate change will alter the predictability, magnitude and other disturbance dimensions, necessitating predictive approaches for management of disturbance impacts. We also highlight the need to better understand the role of freshwater disturbance in managing vulnerable ecosystems, invaders, and restoration.
... On the other hand, weir installation, riparian zone vegetation, and stream sinuosity showed relatively higher differences among sites with and without largemouth bass. The anthropogenic disturbances reportedly facilitate successful fish invasions in the disturbed ecosystems [56]. It appears that IAFS prefer the lentic habitats with hydrological disturbances such as dam construction [17,57] and weir impacts [21] for their rapid spread and concomitant establishment. ...
Invasive alien fish species (IAFS) influence recipient ecosystems in multiple ways, from altered native fish communities to poor ecological health and higher economic losses to control and eradication. We tested key drivers and connections between an IAFS (Micropterus salmoides) presence, absence, geomorphological, hydro-chemical, physical habitat, native fish assemblages, and large river basins biotic integrity during 2016–2019. A total number of 62,121 individuals (TNI) representing 74 fish species were observed, out of which 68 species (45,677 TNI) belonged to the Geum River (GR) basin, while 63 species (16,444 TNI) were from the Mankyong/Dongjin River (MDR) basin. The results illustrated a significant contrast based on stream order, catchment area, altitude, stream gradient, and width among the sites with and without largemouth bass. However, fluctuations in nutrients (nitrogen and phosphorus) were not affected by variations in pH, dissolved oxygen, conductivity, suspended solids, and river flow. The largemouth bass has emerged as the 8th largest fish population in the GR and swiftly occupies the MDR basin with a constancy value of 45.5. Native sensitive (r = −0.38), insectivore (r = −0.252), carnivores (r = −0.085), and TNI (r = −0.512) displayed a negative correlation with increasing largemouth bass abundance. Largemouth bass induced significant regime transformation in the carnivore species. A significant difference (p < 0.01) of biotic integrity was illustrated among the largemouth bass population sites. A conspicuous interplay between ‘poor’ ecological health (r = 0.33, p = 0.038, n = 41) sites and ‘fair–excellent’ (r = −0.38, p < 0.001, n = 622) sites as compared to the overall ecological health linked with largemouth bass abundance (r = −0.397, p < 0.001, n = 663) alluded to stronger impact of the IAFS. In conclusion, the largemouth bass has potentially altered the native fish assemblage and ecological health. Further, we conclude that rapidly shifting flow patterns supported by the expanding anthropogenic interventions (weirs and dam) are the most approving factors of impending fish invasions.
... Disturbances such as these often occur concurrently with the establishment of invasive species in freshwater systems, and can even facilitate invasion (Leprieur et al., 2008;Marchetti et al., 2004;Marvier et al., 2004). River managers thus have the major challenge of determining whether population changes in native species can be attributed to the invasive species themselves or any of the other myriad factors (including water quality and habitat suitability) that F I G U R E 4 Correlation test between the log 10 -transformed catch per unit effort (CPUE) abundances of woundfin and red shiner. ...
• Invasive species are often blamed for the declines of native species, although this is often based on anecdotal or incomplete evidence. In the Virgin River (U.S.A.), the red shiner minnow (Cyprinella lutrensis) has been identified as a major factor in woundfin (Plagopterus argentissimus) decline, a critically endangered endemic minnow. We assessed the evidence for the hypothesis that negative interactions between these two fish drove this decline. We tested three predictions: (1) spatial and temporal patterns were significant predictors of assemblage structure; (2) red shiner would show opposite spatial and temporal patterns to native species; and (3) woundfin would show site-specific decreases in abundance following red shiner invasion.
• We used a long-term (28 years) dataset of fish abundances in the Virgin River at 10 regularly monitored sites to test our predictions. Using principal coordinates of neighbour matrices with redundancy analysis, we tested our first two predictions by identifying the temporal and spatial structure of the fish assemblages and comparing the patterns of native fish species to those of the invasive fish species. To test our third prediction, we used a breakpoint analysis of site-specific population data to determine if woundfin showed stable populations prior to red shiner invasion, followed by declines after invasion.
• We found that 42% of variation in fish abundances in the river could be explained by spatial patterns, and 12% by temporal patterns. Red shiner showed opposite spatial and temporal patterns to woundfin (but not to other native species), and abundances of red shiner and woundfin were negatively correlated, yielding correlative evidence of negative interactions between red shiner and woundfin. However, our breakpoint analysis did not show the expected patterns and woundfin declined even in sites that did not experience red shiner invasion pointing to alternate mechanisms of decline such as effects of poor water quality.
• Our analyses provided correlative but conflicting evidence of red shiner influence on woundfin but were unable to identify a definitive causal mechanism of woundfin decline. We discuss two possible explanations for the contemporary woundfin decline and red shiner invasion: displacement of woundfin via negative interactions, or replacement of woundfin by red shiner in a niche already vacated by woundfin due to environmental or anthropogenic disturbances.
• This study demonstrates that the dynamics between native and non-native species may not be straightforward and can be complicated by other factors such as anthropogenic activities and environmental changes. This research highlights that long-term monitoring is essential to untangling interactions between native and invasive species to develop effective conservation methods that address underlying causes of decline.
... fish species and have also experienced a greater increase in these species over the past few decades. The positive relationship between non-native fish species and river size is a widespread pattern encountered on a global or continental scale between river catchments and on a regional scale between different river sections (Marchetti et al., 2004;Blanchet et al., 2009;Milardi et al., 2019). Two hypotheses are generally put forward to explain this positive relationship. ...
The spread of non-native species is nowadays recognized as a major threat to the biodiversity of freshwater ecosystems. However, for a very long time the introduction and acclimatization of new species has been perceived mainly as a source of wealth for human societies. Here, we examined the establishment of non-native fish species in the Seine River basin from a historical perspective by adopting a twofold approach. In a first step, at the whole basin scale, considering various written and archeological sources, we traced the chronology, over the last millennium, of the establishments of non-native species. In a second step, by analyzing fish monitoring from several hundred sites covering the diversity of rivers and streams, we examined the changes in numbers and abundance of non-native species in local fish communities over the last three decades. The first documented species introduction dates back to the 13th century but it is from the middle of the 19th century that the introduction attempts accelerated. Today, these introductions have reached an unprecedented level and 46% of the species recorded in the basin are non-native. During the last three decades, non-native species have continued to increase within fish communities both in terms of number of species and abundance of individuals. The most pronounced increases are noted on large rivers and sites where anthropic pressures are strong. Waterways connecting European basins, globalization of trade, and ongoing climate change provide a general background suggesting that the increase in the proportion of non-native species in the fish communities of the Seine River basin is likely to continue for several decades.
... The success of introduced fish species has been correlated with the spatial variability of life-history traits (Havel et al., 2005). Such variabilities support introduced species due to higher toleration to changes in biological indices and plasticity of life-history traits such as condition factor and length-weight relationships (Marchetti et al., 2004). ...
The present study aims to investigate the condition, length-weight (LWRs) and length-length relationships (LLRs) of four introduced freshwater fish species (Carassius gibelio, Cyprinus carpio, Gambusia holbrooki, and Pseudorasbora parva) inhabited in the inland waters of Gökçeada (Çanakkale, Turkey). Fish samples were collected using electroshocker from one lentic (Büyük Stream) and four lotic (Aydıncık, Dereköy, Gökçeada, and Uğurlu Reservoirs) ecosystems in September 2019, April 2020, May, 2020, and July 2020. The calculated values of parameter b in the LWRs were 3.275 and 3.230 for G. holbrooki (Uğurlu and Büyük populations, respectively), 3.031 and 2.937 for C. carpio (Aydıncık and Dereköy populations, respectively), 3.129 for C. gibelio and 3.047 for P. parva. Values of Fulton's condition factor (K) varied between 1.72 ± 0.23 (P. parva, Gökçeada population) and 3.60 ± 0.33 (C. carpio, Dereköy population). The coefficients of correlation (r) for all the LLR equations were greater than 0.95 and significantly linear. The present study provides the first knowledge about the selected biological parameters for four introduced freshwater fish species in Gökçeada.
... Despite the fact that a number of fish species have been intentionally introduced to meet the rapidly increasing demand for farmed fish (Lin et al., 2015;Xiong et al., 2015;Grosholz et al., 2015;Zhao et al., 2015;Gozlan, 2016), costs of only five invasive alien fish species have been reported in Asia. This is amidst evidence that multiple introduced fish species escape from aquaculture facilities or are released into the wild (Marchetti et al., 2004;Saba et al., 2021). Similarly, the total lack of reporting on the costs of fish invasions in South America and Africa is surprising given the multiple high-profile examples of fish invasions on these Fig. 2. Observed costs of invasive fish species across regions (North America, Europe, Asia, Antarctic/Sub-Antarctic and Central America) indicating the contribution of the species to the respective total. ...
Invasive alien fishes have had pernicious ecological and economic impacts on both aquatic ecosystems and human societies. However, a comprehensive and collective assessment of their monetary costs is still lacking. In this study, we collected and reviewed reported data on the economic impacts of invasive alien fishes using InvaCost, the most comprehensive global database of invasion costs. We analysed how total (i.e. both observed and potential/predicted) and observed (i.e. empirically incurred only) costs of fish invasions are distributed geographically and temporally and assessed which socioeconomic sectors are most affected. Fish invasions have potentially caused the economic loss of at least US2.28 billion (6.1% of total costs), indicating that the costs of damage caused by invasive alien fishes are often extrapolated and/or difficult to quantify. Most of the observed costs were related to damage and resource losses (89%). Observed costs mainly affected public and social welfare (63%), with the remainder borne by fisheries, authorities and stakeholders through management actions, environmental, and mixed sectors. Total costs related to fish invasions have increased significantly over time, from <US1 billion/year in the 2000s, while observed costs have followed a similar trajectory. Despite the growing body of work on fish invasions, information on costs has been much less than expected, given the overall number of invasive alien fish species documented and the high costs of the few cases reported. Both invasions and their economic costs are increasing, exacerbating the need for improved cost reporting across socioeconomic sectors and geographic regions, for more effective invasive alien fish management.
... We first constructed four different global models, one for each body region, setting every time the brightness of the body region of interest as the dependent variable and verified which variables better explained variation in the system using the dredge function in "MuMIn" (Barton, 2019) ranking by Deviance Information Criterion (DIC). We defined variables as strongly supported if they were present in all mostly supported models (DIC <5) and had a cumulative Akaike weight of > 0.75 (Marchetti et al., 2004;Buxton et al., 2017); less strongly supported if they were present in any of the mostly supported models (DIC <5) and had a cumulative Akaike of > 0.75. Then, to retrieve the posterior means of the significant parameters, we set those as fixed effect for each body region model. ...
... Extensive hybridization and introgression with invasive species can cause reduced individual fitness, population decline, loss of genetically distinct populations, or extirpation (Rhymer and Simberloff 1996;Sinnatamby et al. 2020). Although the processes and predictors of invasion have been widely studied in riverine fishes (Moyle and Light 1996;Marchetti et al. 2004;Rahel and Olden 2008;Peoples et al. 2020), less is known about the factors that make hybridization between native and invasive species more or less likely to occur across the landscape. Understanding the landscape-scale factors affecting hybridization between native and invasive species is key for mitigating negative effects and conserving native species. ...
Bartram’s Bass Micropterus sp. cf. cataractae is endemic to the upper Savannah River basin of the southeastern United States, and is threatened by hybridization with invasive Alabama Bass M. henshalli. Bartram’s Bass have been functionally extirpated from reservoirs, and hybrid individuals have been detected in several tributaries. However, the extent of introgression in tributaries is currently unknown. Our objectives were to (1) assess the distribution of Bartram’s Bass, native Largemouth Bass M. salmoides, invasive Alabama Bass, and their hybrids, in streams of the upper Savannah River basin, and (2) quantify effects of abiotic variables on the distribution of each species. We sampled 154 locations in 2017 and 2018, and assigned genetic identity using hydrolysis probes and microsatellites. We used conditional inference trees (CIT) to quantify variables affecting occurrence of each species and hybrids. We observed widespread hybridization across the basin. Pure Bartram’s Bass were collected at 27% (42) of sites, among which only 12 sites contained pure Bartram’s Bass and no other congeners. Thirty sites where pure Bartram’s Bass were collected contained hybrids. In the montane Blue Ridge ecoregion, occurrence of pure Bartram’s Bass was negatively affected by low levels of local‐scale developed land cover. In the lower‐relief Piedmont ecoregion, pure Bartram’s Bass were positively associated with watershed‐scale forest land cover and stream gradient. Distance to reservoir was positively associated with occurrence of pure Bartram’s Bass in both ecoregions. Pure Bartram’s Bass are likely to occur with high probability in only 16% of non‐impounded stream segments; this represents a conservative estimate and the true number is likely lower. However, future work accounting for incomplete detection of Bartram’s Bass will help to improve confidence in true extirpations. Conservation efforts may be more successful if implemented on stream segments farther from reservoirs or upstream of dispersal barriers preventing colonization of Alabama Bass.
... This is despite a number of sh species having been intentionally introduced to meet the rapid increase in demand for farmed sh (Lin et al. 2015;Xiong et al. 2015), and aquaculture enterprises in Asia producing 80 % of all marine cultured biomass (The State of World Fisheries and Aquaculture 2020) despite being a known vector for aquatic invasions (Grosholz et al., 2015). In fact, costs for only two invasive sh species have been reported in Asia, regardless of evidence of multiple introduced sh species escaping from aquaculture facilities or being released in the wild (Marchetti et al., 2004). Similarly, the absence of reported costs from sh invasions in South America, Africa and Oceania is surprising given multiple notorious examples of sh invasions in these continents. ...
Invasive alien fishes have caused pernicious ecological impacts on aquatic ecosystems. However, there has not been a global appraisal of associated economic impacts. Here, we compiled reported economic impacts of invasive alien fishes using the most comprehensive global database of invasion costs (InvaCost). We analyze how fish invasion costs are distributed geographically and temporally, as well as which socioeconomic sectors are most impacted. Fish invasions have caused the economic loss of at least US0.57 billion/year in the 1980s to US$1 billion/year in the 2000s. Fish invasions have been relatively well studied; however, economic costs have been lower than expected based on overall numbers of alien species. Accordingly, although costs are increasing, improved reporting is required to better understand how fish invasion costs are distributed across time, space and economic sectors.
... All data analysis was undertaken in R version 4.0.0 (R-Core Team, 2020) with the additional package glmulti (Calcagno & de Mazancourt, 2010) to undertake logistic regression of all model combinations, and Akaike's information criterion (AIC) model selection. We then calculate the relative importance of each of the HSI covariates using the inbuilt Multimodal inference and assessed them as highly supported or somewhat support based on Marchetti et al. (2004). ...
The application of a habitat suitability index (HSI) assessment to predict the use of ponds by great crested newts (Triturus cristatus) is commonly used in association with distribution and monitoring projects. Such projects are often used to inform development and planning decision making. However, this type of assessment is frequently misused, and misinterpreted. We used a large, commercially collected environmental DNA (eDNA) survey for great crested newt pond occupancy (489 ponds) to; (1) assess whether it is appropriate to use low HSI scores to rule out occupancy, (2) discuss the use of high HSI scores to identify ponds of high importance for the species and, (3) explore the eDNA detection method. We conclude that there is no evidence to support ruling out pond occupancy based on low HSI scores. However, the conventional view that ponds with HSI scores above 0.7 are of high importance to great crested newts is somewhat supported by the data. Both eDNA and direct observational survey methodologies suffer from sampling error and these need to be acknowledged in the analysis of large data sets.
... We first constructed four different global models, one for each body region, setting every time the brightness of the body region of interest as the dependent variable and verified which variables better explained variation in the system using the dredge function in "MuMIn" 84 ranking by Deviance Information Criterion (DIC). We defined variables as strongly supported if they were present in all mostly supported models (DIC < 5) and had a cumulative Akaike weight of >0.75 85,86 ; less strongly supported if they were present in any of the mostly supported models (DIC < 5) and had a cumulative Akaike of >0.75. Then, to retrieve the posterior means of the significant parameters, we set those as fixed effect for each body region model. ...
The thermal environment can affect the evolution of morpho-behavioral adaptations of ectotherms. Heat is transferred from substrates to organisms by conduction and reflected radiation. Because brightness influences the degree of heat absorption, substrates could affect the evolution of integumentary optical properties. Here, we show that vipers (Squamata: Viperidae) inhabiting hot, highly radiative and superficially conductive substrates have evolved bright ventra for efficient heat transfer. We analyzed the brightness of 4161 publicly available images from 126 species, and we found that substrate type, alongside latitude and body mass, strongly influences ventral brightness. Substrate type also significantly affects dorsal brightness, but this is associated with different selective forces: activity-pattern and altitude. Ancestral estimation analysis suggests that the ancestral ventral condition was likely moderately bright and, following divergence events, some species convergently increased their brightness. Vipers diversified during the Miocene and the enhancement of ventral brightness may have facilitated the exploitation of arid grounds. We provide evidence that integument brightness can impact the behavioral ecology of ectotherms.
... It is very likely, and at the same time very worrying, that many exotic species (listed in detail below) are now well established within the river basins, providing propagules that promote and/or maintain patterns of species distribution that are supported by the predictions of the island biogeography theory. This is confirmed by several studies performed in different geographic areas where the introduction of exotic species for sport fishing was a long-established practice (Marchetti et al. 2004;Westley and Fleming 2011;Castaño-Sánchez et al. 2018). Moreover, there are also some clues that the introduction of exotic species, often indigenous to slow-flowing lowland rivers, can alter the distribution pattern of native species, pushing some of them higher towards the limits of their optimal altitudinal range There are not many comprehensive studies that investigate trends of exotic and native fish species in Italy. ...
The introduction of exotic fish species into Italian river systems presents an additional threat to freshwater native fish species, a wildlife group already under conservation pressure from myriad other anthropogenic factors. Few large-scale and long-term monitoring programmes exist that adequately describe the impact of exotic fish species on native fish. To fill this gap, we analysed the bulk of available data (1985–2014) on fish collected at a national level within the BioFresh Project with the aim of investigating the effects of human-introduced exotic fish species on native species. The results showed that both the Continental and Mediterranean biogeographic regions are home to fish communities which, in conservation terms, are a cause for concern, while Alpine Regions are less so. Generally, the richness of exotic species is still growing in Italy, with about 50% of them having a positive trend while native species’ trends are in the opposite direction – that is, the spread of many exotic species is positively correlated with the decline in many co-occurring native species.
• Key policy insights
• Worrying increase in the richness of exotic species between the 1985 and the 2014.
• A large segment of the current exotic fish contingent is self-sustaining.
• Common bream, Black bullhead, Goldfish, Largemouth bass, Rainbow trout, Roach, Pike perch and European catfish negatively affect the presence probability of at least 50% of co-occurring native species over time.
• The restoration of habitat characteristics and native fish assemblages as well as more rigorous controls during population reinforcement for recreational fishing are needed to prevent or counteract the further spread of exotic fishes.
... The Great Lakes Environmental Assessment and Mapping project (GLEAM; Allan et al. 2013), which provides spatially referenced measures of human disturbance across the Great Lakes, is another rich source of basin-wide spatially referenced data. GLEAM could be used to develop site specific measures of anthropogenic disturbance, a well-recognized correlate of invasibility (Marchetti et al. 2004;Havel et al. 2005;Clark and Johnston 2011). Our understanding of the distribution of non-native fish and invertebrates for the US waters of the Great Lakes continues to improve as the USFWS implements and expands their regional surveillance program (e.g. ...
Risk-based prioritization for early detection monitoring is of utmost importance to prevent and mitigate invasive species impacts and is especially needed for large ecosystems where management resources are not sufficient to survey all locations susceptible to invasion. In this paper we describe a spatially-explicit and quantitative approach for identifying the highest risk sites for aquatic invasive species (AIS) introduction into the United States' waters of the Laurentian Great Lakes, a vast inland sea with a surface area of 246,049 square km and a shoreline length of 16,431 km. We compiled data from geospatial metrics available across all of the US waters of the Great Lakes as surrogates for propagule pressure from the dominant AIS pathways. Surrogates were weighted based on the observed or expected contribution of each pathway to past (historic) and predicted future invasions. Weighted surrogate data were combined to generate "invasion risk" scores for plants, invertebrates, fish, and all taxa combined at 3,487 management units (9 km × 9 km). The number of sites with invasion risk scores > 0 is: for plants (490), for invertebrates (220), for fish (436), and for all taxa (403). The rank order of sites with the highest risk scores varies by taxa, but in general the top thirty highest risk sites are the same across all groups. For all taxonomic groups, we show that the "top 30" sites account for at least 50% of predicted propagule pressure to the basin from all pathways. Many of the highest risk sites are located in western Lake Erie, southern Lake Michigan, and the St. Clair-Detroit River System. This framework provides a starting point for objective surveillance planning and implementation that can be adaptively improved.
... Biological invasion studies aim to specify the most suitable environments for invasion, and identify traits associated to establishment success and high invasiveness (Marchetti et al., 2004;Fleming & Dibble, 2015). Azzurro et al. (2014) discuss the external morphology as a criterium for explaining the success of biological invasions, since it is considered as a proxy for a species ecological position in a community. ...
... Biological invasion studies aim to specify the most suitable environments for invasion, and identify traits associated to establishment success and high invasiveness (Marchetti et al., 2004;Fleming & Dibble, 2015). Azzurro et al. (2014) discuss the external morphology as a criterium for explaining the success of biological invasions, since it is considered as a proxy for a species ecological position in a community. ...
... Although some successful fish invaders can present a rapid realized niche shift in the invaded range, many non-native species survive most easily in an ecosystem that is similar to their native habitat [31,32]. Furthermore, a non-native species' trophic position influences their survival capacity outside their native range in a context of limited food resources [33][34][35]. ...
Non-native fish invasions are among the greatest threats to the sustainability of freshwater ecosystems worldwide. Tilapia and catfish are regularly cultured in South China which is similar to their climate in native areas and may also support their invasive potential. We systematically collected fish from eight main rivers of South China, from 2016 to 2018, to investigate and analyse species’ composition and the distribution of non-native fishes. The data reveal that non-native fishes are widespread and abundant in the sampled rivers: of the 98,887 fish collected, 11,832 individuals representing 20 species were not native, which were distributed in the 96% sampled sites. Of the non-native fish species, 17 are used in aquaculture and 19 are native to the tropics; 13 are omnivores while the other seven are predators. Based on dissimilarity of the non-native fish species distributions across the eight rivers, the different rivers could be divided into four assemblages. Geographical isolation and temperature were identified as affecting the distribution patterns of non-native fishes, thereby influencing fish species composition, species number, dominant species, and distribution variations in the South China rivers. Species composition of the non-native fishes in these rivers are related to their introduction vector, compatibility with their native habitat, and feeding strategies. Their distribution was mainly influenced by geographical location and temperature. To mitigate the impacts of non-native fish, a series of stricter management practices, systematic monitoring, and more research are needed.
... Biological invasion studies aim to specify the most suitable environments for invasion, and identify traits associated to establishment success and high invasiveness (Marchetti et al., 2004;Fleming & Dibble, 2015). Azzurro et al. (2014) discuss the external morphology as a criterium for explaining the success of biological invasions, since it is considered as a proxy for a species ecological position in a community. ...
Feeding habits of the invasive spider crab Libinia dubia from the Mediterranean Sea were studied in the Gulf of Gabès (Tunisia) using the frequency of occurrence and points methods. The population was sampled at least monthly between November 2015 and October 2016. Stomach contents of 384 specimens were analysed. Results indicate that L. dubia is an herbivorous species exhibiting clear preferences for algae (ALG) and Magnoliophyta (MAG) (62.03%, 7.13 points and 59.36%, 5.3 points respectively) although Echinodermata (ECH), Porifera (POR), Cnidaria (CNI), Mollusca (MOL), Polychaeta (POL), Crustacea (CRU) and fish (FIS) were accidentally consumed along with Bryozoa (BRY), sediment (SED), and unidentifiable materials (UNM). The diversity of ALG ingested was studied in detail: Chlorophyceae were found in 87.93% of stomachs containing ALG and contributed most of points to the stomach contents (4.18 points) followed respectively by Phaeophyceae (81.03%, 2.27 points) and Rhodophyceae (40.95%, 0.68 points).Very low Vacuity Index was recorded (VI = 2.6%). Ingested items varied significantly with regard to the season (Chi-square test, χ2calculated = 87.86 > χ2theoretical = 7.81, df = 3, p < 0.05) and crab size (χ2calculated = 14.25 > χ2theoretical = 5.99, df = 2, p = 0.026). Insignificant differences were registered by studying Carapace Width-Stomach Weight (CW-SW) relationships (T-test, tcalculated < ttheoretical, p > 0.05). Kruskal-Wallis test was applied so that the composition of crab diet among groups could be compared (H = 1.1, df = 3, p = 0.77).
... The factors that drive carp invasion success across broad geographical landscapes are often difficult to identify due to complex biological and environmental interactions. Typically, physical and biological characteristics of previously invaded regions and life history information of the species are used to create an ecological niche model, which can predict invasion potential and identify "at risk" environments (Marchetti et al. 2004;Herborg et al. 2007;Kulhanek et al. 2011a, b;Reshetnikov and Ficetola 2011). Ecological niche modeling suggests that most of North America is suitable for carp to invade (Zambrano et al. 2006). ...
Processes that regulate common carp (Cyprinus carpio) recruitment (i.e. survival of eggs, larvae and juveniles) are largely unknown. In interconnected lake-marsh systems of Minnesota, young of year (YOY) carp are generally found in marshes that winterkill and lack bluegill sunfish (Lepomis macrochirus), an abundant native predator. This suggests that bluegills might function as a biocontrol agent for carp. Further, whereas YOY carp are commonly found in winterkill marshes of south-central Minnesota, they are not found in similar systems in northern Minnesota where lake productivity is much lower, suggesting an aquatic productivity bottleneck on carp recruitment. Finally, in marshes where carp recruit (productive and bluegill-free), YOY must disperse into adjacent lakes to drive high population abundance. In this study, I conducted three experiments to test 1) the effect of bluegills on carp recruitment; 2) the effect of aquatic productivity on larval carp survival, growth and diet; 3) natural dispersal tendencies of YOY carp from a marsh into an adjacent lake. The first experiment employed four (20 m diameter) impermeable enclosures from 2011-2014. Each year, enclosures were stocked with carp eggs and every other one was stocked with bluegills. Backpack electrofishing surveys conducted five weeks later showed that carp catch per unit of effort (CPUE) was over 10-fold lower in the enclosures stocked with bluegills than in the controls. The second experiment, conducted in 2014 and 2015 used aquaria stocked with carp larvae and supplied with zooplankton densities and community structures from lakes of three different trophic states (oligo-, meso-, and eutrophic). It showed that carp larvae selectively consumed macrozooplankton (> 200 μm) and their growth rates were highest in the eutrophic lake and lowest in the oligotrophic lake. Survival, however, was high in all treatments. The third study was conducted in a natural lake-marsh system and utilized passive integrated transponder (PIT) tags to quantify the outmigration of YOY carp from the marsh to the lake. It showed that < 6% YOY carp outmigrated to the lake, supporting previous indirect estimates. The results of these three studies are important to understanding recruitment dynamics of carp in lake-marsh systems in Minnesota.
... On the one hand, results from numerous studies suggest a role for biotic resistance in freshwater fish communities (Ricciardi & Atkinson, 2004;Vila-Gispert et al., 2005;Olden et al., 2006). On the other hand, positive relationships between native and nonnative diversity support a role for trait preadaptation (Gido et al., 2004;Marchetti et al., 2004a;dos Santos et al., 2018). Discrepancies among studies may be a function of spatial scale. ...
Establishment of nonnative fishes and extirpations of native fishes have homogenized freshwater fish faunas, yet our understanding of the drivers of this process remain limited. We addressed this knowledge gap by testing three hypotheses about introductions and homogenization of fish communities is the eastern United States: First, whether nonnative fish introductions have caused fish faunas to become homogenized or differentiated; second, whether patterns of faunal change are related to native species richness, propagule pressure, and anthropogenic disturbance; third, whether invasion patterns are attributable to either biotic resistance or preadaptation. We compared taxonomic similarity among watersheds in historical and contemporary time steps, and modeled contributions of different drivers to faunal change within watersheds. Average similarity among watersheds nearly doubled in contemporary times, pointing to substantial fish faunal homogenization. No watersheds lost species; patterns of homogenization are attributable entirely to nonnative species invasion. Community change and nonnative richness were positively associated with agriculture-urban land use, recreational fishing demand, and elevation. Native richness negatively affected community change and nonnative richness. Nonnative species originated from watersheds with higher richness than the ones they invaded, suggesting a role for biotic resistance. Understanding how mechanisms operate across spatial scales will help guide future conservation efforts.
... As adults they develop large, molar-like teeth and eat aquatic plants, macroalgae, and hard-shelled invertebrates (Mylo-phara-don means "mill-throat-teeth"). California's freshwater fish fauna has been severely diminished by human activities, with seven species extinct, thirtythree more (26%) at immediate risk of extinction, and another thirty-three species on a path to extinction if current trends continue (Figure 33.6; Moyle et al. 2011). Native fishes are particularly threatened by flow modifications, especially dams and diversions, the introduction of exotic species, and agricultural and urban development and operations (Box 33.3; May and Brown 2002, Kats and Ferrer 2003, Riley et al. 2005, Moyle et al. 2011 ]) adapted to the slack water conditions that follow flow modification, rather than the strong flow variation characteristic of natural western rivers , Marchetti et al. 2004, Light and Marchetti 2007. The distributions of introduced fish species in California are often determined by the locations of introductions, hydrologic connections, perennial flow patterns, and dispersal limitations (Riley et al. 2005, Marchetti et al. 2006, Moyle and Marchetti 2006. ...
... For example, recent studies show that when the application of phosphorus inputs exceeds agricultural demand, the accumulated excess phosphorus can continue to be mobilized into rivers for a long time after the concentration applied to the soil has been reduced (Powers et al. 2016;King et al. 2017). Thus, agropastoral and urban land use types have been identified as the main factors associated with the reduction of river water quality (Marchetti et al. 2004;Tran et al. 2010;Halstead et al. 2014). ...
Changes to land use generate imbalances in the natural dynamics of aquatic ecosystems. These changes can vary according to the specific characteristics of each environment and due to seasonal factors, reinforcing the importance of studies in this area in different regions of the globe. Thus, the aim of this study was to analyze the effects of land use change on the rivers and streams of the Cachoeira River Basin in the Northeast of Brazil. Samples were collected bi-monthly at 16 points along the basin over 1 year and analyzed for physical and chemical parameters (temperature, pH, conductivity, and percentage saturation of dissolved oxygen), inorganic nutrients (NO3⁻, NO2⁻, NH4⁺/NH3, PO4³⁻, SiO4) and dissolved major ions (Ca²⁺, K⁺, Mg²⁺, Na⁺, HCO3⁻). The highest concentrations of NO3⁻, NO2⁻, NH4⁺/NH3, and PO4³⁻ occurred at the points with the highest percentage of urban areas and population density. The major ions Ca²⁺, K⁺, Mg²⁺, Na⁺, and HCO3⁻ were positively correlated with the percentage of pasture coverage; however, the high concentrations of these ions and the strong correlation between them revealed that other factors besides land use, such as soil cover, geological formation, and water deficit, may be jointly contributing to increases in their concentrations. Thus, the results show that urbanization represents the type of land use with the greatest negative effect on water quality since it alters the concentrations of inorganic nutrients dissolved in the Cachoeira River Basin.
... Muitas espécies introduzidas que se tornam invasoras têm a capacidade de tolerar condições e características de ambientes diferentes (Williamson e Fitter 1996;Marchetti et al. 2004a;Gutierre et al. 2014). Enquanto muitas espécies não se tornam invasoras, outras têm maior potencial para invadir (Olden et al. 2006;Simberloff e Rejmánek 2011). ...
Estudos sobre biologia reprodutiva podem fornecer explicações sobre o sucesso na colonização de novas áreas, dado que características biológicas associadas às espécies invasoras podem conferir vantagem na invasão. Objetivamos avaliar variações de características reprodutivas de peixes invasores em lagoas e rios livres de barragens. Foram estudadas populações de Serrasalmus marginatus, Loricariichthys platymetopon, Ossancora eigenmanni, Auchenipterus osteomystax e Trachelyopterus galeatus em habitat lêntico (Lagoas 1 e 2) e lótico (rios Pirapozinho e Anhumas) durante as estações seca e chuvosa. Fêmeas predominaram na maioria das populações (χ 2 , α < 0,05). Fêmeas de L. platymetopon e T. galeatus apresentaram maior índice gonadossomático durante a estação chuvosa no rio Anhumas e na Lagoa 2, respectivamente (teste de Mann-Whitney, α < 0,05). Populações de S. marginatus, L. platymetopon, O. eigenmanni e T. galeatus apresentaram atividade reprodutiva muito intensa na Lagoa 1. Trachelyopterus galeatus apresentou atividade reprodutiva muito intensa nas duas lagoas e no rio Pirapozinho. Enquanto algumas espécies exibem alto investimento reprodutivo, independentemente do tipo de habitat (T. galeatus), outras podem apresentar variações (S. marginatus e L. platymetopon). Fêmeas em maiores razões sexuais, alto investimento reprodutivo, cuidado parental, fertilização interna e desova parcelada podem ser características que favorecem o estabelecimento na área receptora. Serrasalmus marginatus e L. platymetopon apresentam estratégia de história de vida intermediária Equíbrio/Sazonal e Equilíbrio, respectivamente, enquanto A. osteomystax e T. galeatus apresentam estratégia Sazonal. Por apresentarem indivíduos que se dispersam, sobrevivem e se reproduzem em diferentes tipos de habitat, essas espécies possuem extensa área de ocorrência e invadiram com sucesso a bacia do alto rio Paraná. Portanto, são necessárias ações que controlem as populações e minimizem seus impactos.
... In many cases, the detrimental effects of non-natives have been found to be related to landscape-level habitat change (e.g. urban development, water diversion and stream flow modification for agriculture; Marchetti et al., 2004;Kennard et al., 2005;Light and Marchetti, 2007;Hermoso et al., 2011). Non-natives can also modify the homogenisation or heterogenisation effect of land use on biodiversity at regional scales (Olden and Poff, 2003;Marchetti et al., 2006;Hermoso et al., 2012). ...
Increasing agriculture and urbanization inevitably lead to changes in the biodiversity of stream ecosystems. However, few studies examined comprehensively how biodiversity is distributed within and among protected, agricultural and urban land use types in streams. We studied environmental characteristics of streams and patterns of species richness and other community attributes of stream fish communities in these three characteristic land use types in the catchment of the Danube River, Hungary. Land use separated streams to some degree based on their environmental characteristics. However, both between stream environmental and fish community variability were high in most types, and comparable to land use type level differences in case of many streams. A variety of environmental gradients influenced fish community structure rather independently of land use type, which was also influenced by spatial drivers. Non-native fishes modified the structure of native fish communities, especially in agricultural streams, although their modification effect varied more among individual streams than among land use types. In conclusion, land use type proved to be a poor predictor of fish communities in this human modified landscape. We found that even intensively managed areas (i.e. agricultural and urban) can contribute to the maintenance of fish diversity in this biogeographic region, or at least their potential can be comparable to those streams which flow in protected areas. Thus, conservation management should focus on maintaining streams in more natural condition in protected areas and/or use the potential of non-protected agricultural and urban streams in maintaining fish diversity in human modified landscapes.
... Non-indigenous species pose one of the most serious threats to native ecosystems worldwide (Mack et al. 2000). The establishment of species beyond their native ranges often results in immense negative ecological effects with subsequent decline or even extermination of native species (Clavero and García-Berthou 2005), with aquatic environments being particularly vulnerable (Marchetti et al. 2004a). Indeed, invasions by non-indigenous species are considered a driver of biodiversity loss in freshwater habitats (Strayer 2010). ...
Non-indigenous western tubenose goby Proterorhinus semilunaris and round goby Neogobius melanostomus have rapidly increased in numbers and displaced native ichthyofauna in invaded ecosystems. This displacement has been predominantly linked to competition for resources and shelters. Similarly, P. semilunaris was displaced in many localities after introduction of N. melanostomus but the mechanisms of displacement are still not clear. Within the present study shelter competition laboratory studies were completed with P. semilunaris as resident fish before the introduction of either a sized matched P. semilunaris or N. melanostomus intruder. The fish competed for shelters which resembled a rock or plant. Time in shelter and accounts of direct aggression, indirect aggression and the guarding of shelter were also recorded for each fish. Shelter competitions showed P. semilunaris spent more time in plant shelters but N. melanostomus spent similar time periods in both shelter types. In intraspecific pairings, resident fish spent significantly more time in the shelters and exhibited significantly higher direct aggression and shelter guarding, especially for plant shelters. In interspecific pairings, there was no significant difference in the time spent in shelter by resident P. semilunaris and intruder N. melanostomus in either shelter type at day or night. However, in interspecific pairings, the intruder fish showed significantly higher levels of all aggression types. In intraspecific pairing, the concept of ‘resident wins’ was observed. However, in interspecific pairings, N. melanostomus was able to displace the resident fish. The higher aggression of N. melanostomus in shelter competition could account for greater invasive success and the reduction of P. semilunaris observed in the wild.
... The potential establishment of non-native species in new geographic locations is closely related to environmental quality (e.g., Herborg et al. 2007;Kilroy et al. 2008;Kulhanek et al. 2011) and may be related to disturbance (Hobbs and Huenneke 1992;Minchinton 2002;Marchetti et al. 2004a). Land-use changes such as the conversion of natural habitats to pastures and croplands constitute a key factor disturbing natural terrestrial and aquatic environments. ...
The aim of this study was to test the hypothesis that a widespread non-native fish species in Brazil displays opportunistic feeding behavior and changes its diet according to environmental conditions. We compared the diet, feeding selectivity, carbon assimilation, trophic niche, and trophic level of Knodus moenkhausii (a small non-native characid fish species of Upper Paraná River) in streams surrounded by natural riparian vegetation (natural cover streams) and in streams impacted by pasture. We analyzed stomach contents and stable isotopes (carbon and nitrogen), simultaneously. Overall, insects were the most common food items (> 65%). In natural cover streams, K. moenkhausii showed higher selectivity among aquatic macroinvertebrates consumed, while in pasture streams, they fed on the most abundant groups. The proportion of feeding groups assimilated by K. moenkhausii and the proportion of primary sources consumed by each feeding group of macroinvertebrates also varied between natural cover and pasture streams, as indicated by stable isotopes. In natural cover streams, fine and coarse particulate organic matter accounted for approximately 80% of K. moenkhausii’s diet, while in pasture streams, algae and periphyton also contributed greatly. As a result, K. moenkhausii occupied a higher trophic level and exhibited a broader niche width in pasture streams. We conclude that K. moenkhausii presents feeding selectivity with capacity to alter the trophic niche depending on environmental conditions. Such opportunism could be one of the reasons underpinning the abundance and wide distribution of this invasive species.
... In many cases, the detrimental effects of non-natives have been found to be related to landscape-level habitat change (e.g. urban development, water diversion and stream flow modification for agriculture; Marchetti et al., 2004;Kennard et al., 2005;Light and Marchetti, 2007;Hermoso et al., 2011). Non-natives can also modify the homogenisation or heterogenisation effect of land use on biodiversity at regional scales (Olden and Poff, 2003;Marchetti et al., 2006;Hermoso et al., 2012). ...
Increasing agriculture and urbanization inevitably lead to changes in the biodiversity of stream ecosystems. However, few studies examined comprehensively how biodiversity is distributed within and among protected, agricultural and urban land use types in streams. We studied environmental characteristics of streams and patterns of species richness and other community attributes of stream fish communities in these three characteristic land use types in the catchment of the Danube River, Hungary. Land use separated streams to some degree based on their environmental characteristics. However, both between stream environmental and fish community variability were high in most types, and comparable to land use type level differences in case of many streams. A variety of environmental gradients influenced fish community structure rather independently of land use type, which was also influenced by spatial drivers. Non-native fishes modified the structure of native fish communities, especially in agricultural streams, although their modification effect varied more among individual streams than among land use types. In conclusion, land use type proved to be a poor predictor of fish communities in this human modified landscape. We found that even intensively managed areas (i.e. agricultural and urban) can contribute to the maintenance of fish diversity in this biogeographic region, or at least their potential can be comparable to those streams which flow in protected areas. Thus, conservation management should focus on maintaining streams in more natural condition in protected areas and/or use the potential of non-protected agricultural and urban streams in maintaining fish diversity in human modified landscapes.
Water diversion for hydropower plants is one of the leading causes of habitat alteration and biotic homogenization. The impacts of small hydropower plants on fish communities are usually assessed using taxonomic composition and structure indicators. Size-based indicators are useful tools to evaluate the effects of environmental factors and anthropogenic perturbations on riverine ecosystems. In this study, we investigated the impact of water diversion on fish community body size structure in 16 small hydropower plants in the upper Ter River basin (NE Iberian Peninsula). We tested the use of multiple size-based metrics under different sampling intensities (one- vs. four-pass electrofishing) and compared control vs. diverted stream stretches. Results revealed that water diversion had a negative effect on fish community average and median length, while size spectrum and size diversity metrics showed no responses to the impact. Altitude was positively related with body size metrics and was the strongest natural driver affecting them. Moreover, we found that all the size-based metrics exhibited consistent values under different sampling efforts. Our findings suggest that size-based metrics could be useful indicators for bioassessment of river flow alteration and that one-pass electrofishing was robust enough to characterize the stream fish community size structure in our study.
Reservoirs in the Mississippi River basin are facing three momentous threats. The first two, aging and climate change, are relatively slow moving and their signal can be hard to discern given their stretched temporal scales. The third, species invasions, is faster paced and discernable within shorter temporal scales and restricted spatial scales. Aging and climate directly affect reservoir environments and indirectly their biotic communities. Climate change is expected to interact with aging to speed up and, in some instances, slow down aging. Conversely, invasions primarily imperil biotic communities but can also impact environmental elements. This triple jeopardy is expected to transform reservoir environs and their biotic assemblages in various, often uncertain, ways. I take a broad view of these threats within the Mississippi River basin. A basin‐scale perspective, in contrast to a single reservoir or regional scale, may enhance awareness of reservoirs at a larger level and produce understanding less evident at local levels, hence possibly offering a wider range of choices for confronting threats. My aim is to (1) provide a synopsis of the assemblage of reservoirs and their attributes over the Mississippi River basin, (2) describe the issues related to aging, climate change, and invasions, and (3) consider a conservation framework for confronting these pressures. Given the overlapping temporal, spatial, and ecological effects of these threats, it is essential to address their effects simultaneously.
Ecological communities are structured by combinations of biotic and abiotic factors acting at different spatial scales. However, the relative influence of the different scale‐related variables on assemblage composition is poorly understood, despite being key to the effective and efficient management of fluvial ecosystems. We took advantage of the relatively recent and well‐studied history of salmonid introductions in Patagonia to evaluate if non‐native species show different patterns of association with abiotic factors depending on the spatial scale of the environmental filter. We used a hierarchical approach to characterised environmental variables at the basin and reach scales to assess their influence on the presence, abundance and structure of the salmonid assemblages in breeding streams. We saw no evidence that presence/absence patterns of salmonid distribution were driven by landscape variables, except for those basins with physical environmental barriers to colonisation. However, we did find evidence for relative abundances being influenced by climatic and geomorphological variables (e.g., precipitation and relief). Our results do not support a scenario in which any of the salmonid species modulates the distribution of the other species, suggesting that interference has played only a minor role in determining current fish distribution in fluvial systems of the region. Instead, current patterns of presence and abundance of salmonids are best explained as the product of environmental filters. Our findings contribute to our understanding of the ecology of individual species and provide insight into the mechanisms structuring fish assemblages in Southern Hemisphere's lotic systems.
Predicting the shift of invasive species distribution in response to climate change is essential for ecological risk assessment. In this study, the distribution of invasive largemouth bass (Micropterus salmoides) was predicted from 2016 to 2085 in the Han River basin of South Korea using HadGEM3-RA based climate change scenarios (representative concentration pathway [RCP] 4.5 and 8.5 scenarios). A random forest model was developed using largemouth bass occurrence data and environmental variables (temperature, precipitation, flow rate, water quality, elevation, and slope) for five years (2011–2015). The annual mean temperature was the second most contributing variable after elevation. The occurrence of largemouth bass in the Han River basin was expected to increase in the future with increasing annual mean temperature, especially after the 2060 s (2056–2065) in the RCP 8.5 scenario. The latitudinal, longitudinal, and altitudinal shifts of largemouth bass distribution were expected to be −1.76 km, 4.19 km, and 9.07 m per 10 years under the RCP 8.5 scenario, respectively, indicating a gradual southeastward shift to higher locations. Given that invasive fish can disturb the habitat of endemic species, three-dimensional distribution shift under climate change should be considered for the ecological risk assessment of invasive species.
Uses spatial modeling (the Genetic Algorithm for Rule-Set Production or GARP), with MODIS environmental data, to predict future distributions of multiple invasive species in the Great Lakes. Nice report! Also covered in the report is a spatial-modeling effort focused on shipping within the Great Lakes, given that most of the species invasions are likely to source to ballast-water exchanges from ships entering the Great Lakes.
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.
Much has been written about the influence of exotic or nonindigenous species on natural habitats and communities of organisms, but little is known of the physical or biological conditions that lead to successful invasion of native habitats and communities by exotics. We studied invasivity factors in headwater streams of the Susquehanna River West Branch, which drains portions of the northern Appalachian Plateau. A replicated (two major tributaries) 3 × 3 factorial design was used to determine landscape effects of size (stream order) and quality (land use) on abiotic (physical and chemical) and biotic (fish community structure and function) stream attributes. Seven (21%) of thirty-four fish species (brown trout, common carp, mimic shiner, bluegill, smallmouth bass, fantail darter, and banded darter) collected in the eighteen streams sampled were nonindigenous to the basin. Watershed size (stream orders 1, 3, and 5) significantly affected stream geomorphologic and habitat variables (gradient, width, depth, current velocity, diel water temperature, bank overhang, canopy cover, and woody debris density) but not water-quality variables, while land use in watersheds (conservation, mining, and agriculture) significantly affected measured water-quality variables (alkalinity and concentrations of manganese, calcium, chloride, nitrate, and total dissolved solids) but not stream physical or habitat quality. Both watershed size and land use affected fish-community variables such as presence of particular species, species density, species diversity, tolerance diversity, and mean fish size, but in both cases the effect was transparent to native-origin status of fish species. No relationships were found between occurrence of nonindigenous species in watersheds and trophic structure or functional diversity. Therefore, the hypothesis that reduced species diversity increases vulnerability to nonindigenous species was not supported. However, the spatial variation associated with both water-quality and habitat-quality factors was greater in streams with mixed (those with nonindigenous species) than with exclusively native assemblages. These findings suggest that the mechanism for successful invasion by nonindigenous or exotic species is through change in water or habitat quality associated with human or natural disturbances, such as agriculture and mining activities in watersheds. Biotic factors appear to play no or a lesser role in the invasibility of northern Appalachian lotic systems.
A controversy exists in the Pacific Northwest of the United States between logging of old-growth coniferous forests and conservation of Northern Spotted Owl (Strix occidentalis caurina) populations. This species has a strong association with old-growth forests that also have economic value as timber. Research questions relevant to conservation of this species include how temporal trends in Northern Spotted Owl populations are influenced and how spatial configuration of old-growth forests affects these populations. To address these questions, we studied a population of marked Northern Spotted Owls on 95 territories in northwestern California from 1985 through 1994. We examined the magnitude of temporal and spatial variation in life history traits (survival, reproductive output, and recruitment), the effects of climate and landscape characteristics on temporal and spatial variation in these traits, respectively, and how this variation affected aspects of population dynamics. We used a components-of-variation analysis to partition sampling from process variation, and a model selection approach to estimate life history traits using capturerecapture and random-effects models. Climate explained most of the temporal variation in life history traits. Annual survival varied the least over time, whereas recruitment rate varied the most, suggesting a 'bet-hedging' life history strategy for the owl. A forecast of annual rates of population change (λ), estimated from life history traits, suggested that Northern Spotted Owl populations may change solely due to climate influences, even with unchanging habitat conditions. In terms of spatial variation, annual survival on territories was positively associated both with amounts of interior old-growth forest and with length of edge between those forests and other vegetation types. Reproductive output was negatively associated with interior forest, but positively associated with edge between mature and old-growth conifer forest and other vegetation types. A gradient existed in territory-specific estimates of fitness derived from these life history estimates. This gradient suggested that a mosaic of older forest interspersed with other vegetation types promoted high fitness in Northern Spotted Owls. Habitat quality, as defined by fitness, appeared to buffer variation in annual survival but did not buffer reproductive output. We postulated that the magnitude of λ was determined by habitat quality, whereas variation of λ was influenced by recruitment and reproductive output. As habitat quality declines, variation in λ should become more pronounced.
Canonical Correspondence Analysis (CCA) is quickly becoming the most widely used gradient analysis technique in ecology. The CCA algorithm is based upon Correspondence Analysis (CA), an indirect gradient analysis (ordination) technique. CA and a related ordination technique, Detrended Correspondence Analysis, have been criticized for a number of reasons. To test whether CCA suffers from the same defects, I simulated data sets with properties that usually cause problems for DCA. Results indicate that CCA performs quite well with skewed species distributions, with quantitative noise in species abundance data, with samples taken from unusual sampling designs, with highly intercorrelated environmental variables, and with situations where not all of the factors determining species composition are known. CCA is immune to most of the problems of DCA.
Observations from islands, small-scale experiments, and mathematical models have generally supported the paradigm that habitats of low plant diversity are more vulnerable to plant invasions than areas of high plant diversity. We summarize two independent data sets to show exactly the opposite pattern at multiple spatial scales. More significant, and alarming, is that hotspots of native plant diversity have been far more heavily invaded than areas of low plant diversity in most parts of the United States when considered at larger spatial scales. Our findings suggest that we cannot expect such hotspots to repel invasions, and that the threat of invasion is significant and predictably greatest in these areas.
Biotic homogenization is the increased similarity of biotas over time caused by the replacement of native species with nonindigenous species, usually as a result of introductions by humans. Homogenization is the outcome of three interacting processes: introductions of normative species, extirpation of native species, and habitat alterations that facilitate these two processes. A central aspect of the homogenization process is the ability of species to overcome natural biogeographic barriers either through intentional transport by humans or through colonization routes created by human activities. Habitat homogenization through reservoir construction contributes to biotic homogenization as local riverine faunas are replaced with cosmopolitan lentic species. The homogenization process has generally increased biodiversity in most freshwater faunas, as the establishment of new species has outpaced the extinction of native species. There are important exceptions, however, where the establishment of nonindigenous species has had devastating impacts on endemic species. The homogenization process appears Rely to continue, although it could be slowed through reductions in the rate of invasions and extirpations and by rehabilitating aquatic habitats so as to favor native species.
Twenty sites in the lower San Joaquin River drainage, California, were sampled from 1993 to 1995 to characterize fish communities and their associations with measures of water quality and habitat quality. The feasibility of developing an Index of Biotic Integrity was assessed by evaluating four fish community metrics, including percentages of native fish, omnivorous fish, fish intolerant of environmental degradation, and fish with external anomalies. Of the thirty-one taxa of fish captured during the study, only 10 taxa were native to the drainage. Multivariate analyses of percentage data identified four site groups characterized by different groups of species. The distributions of fish species were related to specific conductance, gradient, and mean depth; however, specific conductance acted as a surrogate variable for a large group of correlated variables. Two of the fish community metrics – percentage of introduced fish and percentage of intolerant fish – appeared to be responsive to environmental quality but the responses of the other two metrics – percentage of omnivorous fish and percentage of fish with anomalies – were less direct. The conclusion of the study is that fish communities are responsive to environmental conditions, including conditions associated with human-caused disturbances, particularly agriculture and water development. The results suggest that changes in water management and water quality could result in changes in species distributions. Balancing the costs and benefits of such changes poses a considerable challenge to resource managers.
Canonical correspondence analysis (CCA) is a multivariate method to elucidate the relationships between biological assemblages of species and their environment. The method is designed to extract synthetic environmental gradients from ecological data-sets. The gradients are the basis for succinctly describing and visualizing the differential habitat preferences (niches) of taxavia an ordination diagram. Linear multivariate methods for relating two set of variables, such as two-block Partial Least Squares (PLS2), canonical correlation analysis and redundancy analysis, are less suited for this purpose because habitat preferences are often unimodal functions of habitat variables. After pointing out the key assumptions underlying CCA, the paper focuses on the interpretation of CCA ordination diagrams. Subsequently, some advanced uses, such as ranking environmental variables in importance and the statistical testing of effects are illustrated on a typical macroinvertebrate data-set. The paper closes with comparisons with correspondence analysis, discriminant analysis, PLS2 and co-inertia analysis. In an appendix a new method, named CCA-PLS, is proposed that combines the strong features of CCA and PLS2.
The extent to which species richness in local communities is determined by regional and historical processes is not well understood. An increasingly popular way to investigate these large-scale processes is through regressions of local on regional species richness. We sampled local and regional species richness in a broad array of taxa from around the world to address five questions. First, is the relationship between local and regional species richness linear, or does local richness accumulate more slowly at progressively higher regional diversities, suggesting local saturation of species diversity? Second, do these relationships vary with locality size? Third, do taxa and continents differ in the form of relationships between local and regional diversity? Fourth, do relationships between local and regional diversity depart from that expected from a null model in which all individuals of a locality are randomly sampled from a regional pool of species whose abundances have a canonical log-normal distribution? Fifth, using this same null model, how does the expected relationship between local and regional species richness depend on the sampling intensity within localities? We used distribution maps to ensure that diversity was sampled in a consistent manner across diverse taxa. Each region was 500 × 500 km, and localities were 1% and 10% of the region size. There was no evidence of local species saturation, as local species richness was strongly and linearly related to regional richness at both spatial scales. Between scales, local diversity accumulated faster as a function of regional diversity at the larger spatial scale. The slope of this relationship between local and regional diversity was the same among taxa across continents, and between Australia and North America across taxa. In other words, at each spatial scale one relationship between local and regional diversity describes most cases very well. The null model showed that approximately linear relationships between local and regional diversity are expected when regional species abundances are log-normal and when the number of individuals sampled within localities is large (roughly 200 times the number of species in the most species-rich region examined). However, empirical slopes were less than expected from the null model, which we interpret as an effect of spatial turnover of species (beta diversity). Since these slopes were nevertheless similar among taxa and between regions, rates of spatial turnover must be approximately the same among these taxa and regions. The log-normal model also showed that nonlinear (concave down) relationships between local and regional diversity are expected under random sampling when sample size is small relative to regional diversity. Therefore, nonlinear relationships are not necessarily indicative of saturation. Our results suggest that at the scales investigated here local communities are unsaturated and that their diversities are strongly limited by species richness of the surrounding regions. Similarity between taxa and continents in the form of the local-regional diversity relationship implies that "rules" governing the assembly of local communities may be widely consistent. If so, understanding species diversity in local assemblages will require knowledge of processes acting at larger spatial scales, including determinants of regional species richness and spatial turnover of species.
A survey was made of the fishes occurring in streams of the Sierra Nevada foothills above the San Joaquin Valley, California. Twenty-four species were collected, 12 native, 12 introduced. The present distributions of these fishes were compared to their pre-1900 distributions, as inferred from old records. Overall, the ranges of introduced species and rainbow trout have expanded while the ranges of native species, especially California roach, hardhead, Sacramento squawfish and Sacramento sucker, have contracted. Healthy populations of native fishes were found only in a rather narrow middle elevation band of comparatively undisturbed sections of foothill streams. The native fish populations in different foothill stream systems are now isolated from each other and are, thus, in danger of local extinction as foothill development proceeds. The study indicates that populations of native stream fishes, even if they do not contain endangered species, should be protected, to make sure that severe natural conditions, when combined with human alterations of the streams, do not destroy unique assemblages of fishes.
Some theories and experimental studies suggest that areas of low plant species richness may be invaded more easily than areas of high plant species richness. We gathered nested-scale vegetation data on plant species richness, foliar cover, and frequency from 200 1-m2 subplots (20 1000-m2 modified-Whittaker plots) in the Colorado Rockies (USA), and 160 1-m2 subplots (16 1000-m2 plots) in the Central Grasslands in Colorado, Wyoming, South Dakota, and Minnesota (USA) to test the generality of this paradigm. At the 1-m2 scale, the paradigm was supported in four prairie types in the Central Grasslands, where exotic species richness declined with increasing plant species richness and cover. At the 1-m2 scale, five forest and meadow vegetation types in the Colorado Rockies contradicted the paradigm; exotic species richness increased with native-plant species richness and foliar cover. At the 1000-m2 plot scale (among vegetation types), 83% of the variance in exotic species richness in the Central Grasslands was explained by the total percentage of nitrogen in the soil and the cover of native plant species. In the Colorado Rockies, 69% of the variance in exotic species richness in 1000-m2 plots was explained by the number of native plant species and the total percentage of soil carbon. At landscape and biome scales, exotic species primarily invaded areas of high species richness in the four Central Grasslands sites and in the five Colorado Rockies vegetation types. For the nine vegetation types in both biomes, exotic species cover was positively correlated with mean foliar cover, mean soil percentage N, and the total number of exotic species. These patterns of invasibility depend on spatial scale, biome and vegetation type, spatial autocorrelation effects, availability of resources, and species-specific responses to grazing and other disturbances. We conclude that: (1) sites high in herbaceous foliar cover and soil fertility, and hot spots of plant diversity (and biodiversity), are invasible in many landscapes; and (2) this pattern may be more closely related to the degree resources are available in native plant communities, independent of species richness. Exotic plant invasions in rare habitats and distinctive plant communities pose a significant challenge to land managers and conservation biologists.
Biological invasion is a widespread, but poorly understood phenomenon. Elton's hypothesis, supported by theory, experiment, and anecdotal evidence, suggests that an important determinant of invasion success is resident biodiversity, arguing that high diversity increases the competitive environment of communities and makes them more difficult to invade. Observational studies of plant invasions, however, find little support for this hypothesis and argue strongly against it. Lack of control of extrinsic factors (e.g., disturbance, climate, or soil fertility) that covary with biodiversity and invasion in observational studies makes it difficult to determine if their findings truly refute Elton's hypothesis. We examined performance of Crepis tectorum (an invasive, annual composite weed) in experimental prairie grassland plots and greenhouse plant assemblages in which resident species richness was directly manipulated. Under these conditions, unlike observational studies, no covarying extrinsic factors could interfere with interpreting results. We found a strong inverse association between resident diversity and invader performance as predicted by Elton's hypothesis. Higher resident diversity increased crowding, decreased available light, and decreased available nutrients all of which increased the competitive environment of diverse plant assemblages and reduced C. tectorum success. Examination of individual resident species impacts on C. tectorum performance demonstrated that this diversity effect was not due to the sampling effect. These results suggest that both Elton's hypothesis and its competitive mechanism may operate in nature, but covarying extrinsic factors may obscure the negative impact of diversity on invader success.
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.
Threats to imperiled freshwater fauna in the U.S. were assessed through an experts survey addressing anthropogenic stressors and their sources. Specifically, causes of historic declines and current limits to recovery were identified for 135 imperiled freshwater species of fishes, crayfishes, dragonflies and damselflies, mussels, and amphibians. The survey was designed to identify threats with sufficient specificity to inform resource managers and regulators faced with translating information about predominant biological threats into specific, responsive actions. The findings point to altered sediment loads and nutrient inputs from agricultural nonpoint pollution; interference from exotic species; and altered hydrologic regimes associated with impoundment operations as the three leading threats nationwide, accompanied by many lesser but still significant threats. Variations in threats among regions and among taxa were also evident. Eastern species are most commonly affected by altered sediment loads from agricultural activities, whereas exotic species, habitat removal/damage, and altered hydrologic regimes predominate in the West. Altered sediment loading from agricultural activities and exotic species are dominant problems for both eastern mussels and fishes. However, eastern fishes also appear to be suffering from municipal nonpoint pollution (nutrients and sediments), whereas eastern mussels appear to be more severely affected by altered nutrient impacts from hydroelectric impoundments and agricultural runoff. Our findings suggest that control of nonpoint source pollution associated with agriculture activities should be a very high priority for agricultural producers and governmental support programs. Additonally, the large number of hydropower dams in the U.S. subject to federal re-licensing in coming years suggests a significant opportunity to restore natural hydrologic regimes in the affected rivers.Se estimaron amenazas a la fauna dulceacuícola de los Estados Unidos en riesgo mediante un estudio de expertos enfocado en estresores antropogénicos y sus fuentes. Se identificaron específicamente las causas de disminuciones históricas y los límites actuales para la recuperación de 135 especies dulceacuícikolas de peces, langostinos, libélulas, mejillones y anfibios en riesgo. El estudio fué diseñado para identificar amenazas con suficiente especificidad como para informar a los manejadores de recursos y reguladores que encaran la traducción de información sobre amenazas biológicas predominantes en acciones específicas y sensibles. Los resultados apuntan hacia cargas de sedimentos y entrada de nutrientes alterados por fuentes agriculturales sin puntos de contaminación; interferencia de especies exóticas y regímenes hidrológicos alterados asociados a operaciones de retención, como las amenazas más importantes a nivel nacional, acompañadas por muchas otras menores pero aún significativas amenazas. Tambien fueron evidentes variaciones entre regiones y entre taxas. Las especies del este son mas comunmente afectadas por cargas de sedimentos de actividades agriculturales, mientras que las especies exóticas, la remoción/daño del hábitat y alteración de regimen hidrológico predominaron en el oeste. Cargas de sedimentos alteradas por actividades agriculturales y especies exóticas son problemas dominantes tanto en mejillones como en peces del este. Sin embargo, los peces del este aparentemente también sufren de descargas municipales sin puntos de contaminación (nutrientes y sedimentos), mientras que los mejillones parecen ser mas severamente afectados por la ateración de nutrientes debido a retenciones hydroeléctricas y descargas agriculturales. Nuestros resultados indican que el control de fuentes de contaminación sin puntos asociadas a actividades agriculturales deben ser de alta prioridad para los productores agrícolas y programas de soporte gubernamental. Adicionalmente, la gran cantidad de represas en los Estados Unidos sujetas a re-expedición de licencias federales en los próximos años, sugiere una oportunidad significativa para restablecer los regímenes hidrológicos en los ríos afectados.
Hypotheses concerning community-level vulnerability to invasion often emphasize biotic interactions but fail to consider fine-scale variation in the physical environment. In this study, the interplay between interspecific competition and abiotic factors is examined with respect to whether scrub habitats in southern California become invaded by the Argentine ant (Linepithema humile). Argentine ants penetrate further into and attain higher abundances in mesic scrub fragments than they do in xeric scrub fragments. Probably as a result, native ant richness is lower in small (
In the concerns about biodiversity conservation, fresh waters have received less attention than tropical forests and oceans. However, running waters harbor a diverse panoply of species, habitats, and ecosystems, including some of the most threatened and many having great value to human society. An overview of the biological diversity of running waters and the state of imperilment is presented. Six major factors that threaten destruction of running water species and ecosystems are discussed: habitat loss and degradation; species invasions; overharvesting; secondary extinctions; chemical and organic pollution; global climate change. General measures for recovery and restoration of running waters conclude the article.
With a simple model, I show that comparisons of invasibility between regions are impossible to make unless one can control for all of the variables besides invasibility that influence exotic richness, including the rates of immigration of species and the characteristics of the invading species themselves. Using data from the literature for 184 sites around the world, I found that nature reserves had one-half of the exotic fraction of sites outside reserves, and island sites had nearly three times the exotic fraction of mainland sites. However, the exotic fraction and the number of exotics were also dependent on site area, and this had to be taken into account to make valid comparisons between sites. The number of native species was used as a surrogate for site area and habitat diversity. Nearly 70% of the variation in the number of exotic species was accounted for by a multiple regression containing the following predictors: the number of native species, whether the site was an island or on the mainland, and whether or not it was a nature reserve. After controlling for scale, there were significant differences among biomes, but not continents, in their level of invasion. Multiple biome regions and temperate agricultural or urban sites were among the most invaded biomes, and deserts and savannas were among the least. However, there was considerable within-group variation in the mean degree of invasion. Scale-controlled analysis also showed that the New World is significantly more invaded than the Old World, but only when site native richness (probably a surrogate for habitat diversity) is factored out. Contrary to expectation, communities richer in native species had more, not fewer, exotics. For mainland sites, the degree of invasion increased with latitude, but there was no such relationship for islands. Although islands are more invaded than mainland sites, this is apparently not because of low native species richness, as the islands in this data set were no less rich in native species than were mainland sites of similar area. The number of exotic species in nature reserves increases with the number of visitors. However, it is difficult to draw conclusions about relative invasibility, invasion potential, or the roles of dispersal and disturbance from any of these results. Most of the observed patterns here and in the literature could potentially be explained by differences between regions in species properties, ecosystem properties, or propagule pressure.
Species transported to and introduced into non-native environments, termed ‘introductions’, constitute a growing component of many regional floras and faunas, yet not all such species successfully establish. Investigations into why some introductions succeed while others fail are often based on analyses of the outcome of historical introductions. Such ‘experiments in nature’ have the drawback that the effects of interest may be confounded because they have not been randomized with respect to each other, and because the species and locations chosen for introduction may not be a random subset of the available species or locations. Our aim is to quantify this non-randomness using a global data set of bird introductions, and examine the factors associated with introduction probability in two subsets of these data, one taxonomic (order Anseriformes) and one geographical (British birds).
Global.
Statistical analyses of the distributions among taxa and locations for 1378 introduction events for 426 bird species across the world, and statistical analyses of the characteristics of Anseriform and British bird species selected for introduction.
Global introductions of birds have been highly non-random with respect to taxon, location of origin, and location of introduction. Most introductions involve species in just five families (Phasianidae, Passeridae, Psittacidae, Anatidae and Columbidae), and most introductions have been to temperate and island locations. Within the taxonomic and geographical subsets, the species chosen for introduction tend to be abundant species that would have been relatively easy to obtain.
The characteristics of the species and locations chosen for introduction are not representative of species and locations in general, which limits our ability to draw general conclusions from historical records, and generates problems of confounding and non-independence in statistical analyses of introduction success. We suggest possible solutions for these problems.
Information theory and log-likelihood models - a basis for model selection and inference practical use of the information theoretic approach model selection uncertainty with examples Monte Carlo insights and extended examples statistical theory.
Ecologists need to analyze their field data to interpret relationships within plant and animal communities and with their environments. The purpose of this book is to show ecologists and environmental scientists what numerical and statistical methods are most useful, how to use them and interpret the results from them, and what pitfalls to avoid. Subjects treated include data requirements, regression analysis, calibration (or inverse regression), ordination techniques, cluster analysis, and spatial analysis of ecological data. The authors take pains to use only elementary mathematics and explain the ecological models behind the techniques. Exercises and solution are provided for practice. This is the only book written specifically for ecologists that explains such techniques as logistic regression, canonical correspondence analysis, and kriging (statistical manipulation of data). This is a reissue of a book first published in 1987 by Pudoc (The Netherlands). Contents List of contributors; Preface to first edition; Acknowledgement; List of symbols; Dune meadow data; 1. Introduction R. H. G. Jongman; 2. Data collection J. C. Jager and C. W. N. Looman; 3. Regression C. J. F. ter Braak and C. W. N. Looman; 4. Calibration C. J. F. ter Braak; 5. Ordination C. J. F. ter Braak; 6. Cluster analysis O. F. R. van Tongeren; 7. Spatial aspects of ecological data P. A. Burrough; 8. Numerical methods in practice: case-studies P. A. Burrough, J. A. F. Oudhof, A. Barendregt, R. H. G. Jongman and T. J. van de Nes; References; Index.
Community ecology theory can be used to understand biological invasions by applying recent niche concepts to alien species and the communities that they invade. These ideas lead to the concept of ‘niche opportunity’, which defines conditions that promote invasions in terms of resources, natural enemies, the physical environment, interactions between these factors, and the manner in which they vary in time and space. Niche opportunities vary naturally between communities but might be greatly increased by disruption of communities, especially if the original community members are less well adapted to the new conditions. Recent niche theory clarifies the prediction that low niche opportunities (invasion resistance) result from high species diversity. Conflicting empirical patterns of invasion resistance are potentially explained by covarying external factors. These various ideas derived from community ecology provide a predictive framework for invasion ecology.
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.
1. Data from the literature were used to document colonization patterns by introduced freshwater fishes in 125 drainages across temperate North America. We analysed this data set to quantify susceptibility to invasion, success of the invaders and changes in species richness.
2. Drainages with a high number of impoundments, large basin area and low native species diversity had the greatest number of introduced species. Those drainages containing few native fishes exhibited great variation in the number of invaders, while waters with a rich native fauna contained few introduced species. However, this pattern did not differ significantly from random simulations because the pool of potential invaders is greater for drainages with low species richness.
3. In most drainages, there were more introduced than imperilled or extirpated species, suggesting that invaders tend to increase overall species richness.
4. These patterns suggest that North American fish communities are not saturated with species, but instead, are capable of supporting higher levels of diversity if the pool of potential colonists and the rate of colonization from that pool is increased.
Plant species composition, species abundances, and species richness were strongly recruitment limited in a 4-yr experiment in which seeds of up to 54 species were added to patches of native grassland. Four field seasons after a one-time addition of seed, many added species were still present and reproducing, with plots seeded at the highest rate having species richness that was 83% greater and total plant cover that was 31% greater than controls. Total plant community cover increased significantly with the number of species added as seed, but total cover of pre-existing species was independent of the number of species added as seed, suggesting that the new species mainly filled previously ''empty'' sites. The proportion of added species that became established was negatively correlated with initial species richness of plots, suggesting that species-rich sites were more resistant to invasion. Plot invasibility also depended on the abundances and species richness of plant functional groups in the plots, but was independent of seed size and of total plant cover. The major functional groups of plants differed in their abilities to invade as seed, with perennial grasses being the poorest invaders and herbaceous legumes being the best. Thus, local biotic interactions and recruitment dynamics jointly determined diversity, species composition, and species abundances in these native grassland communities. This supports a metapopulation-like perspective over a purely interspecific-interaction perspective or a purely regional perspective, suggesting that recruitment limitation may be more important, even on a local scale, than often recognized.
Anthropogenic introduction of species is homogenizing the earth's biota. Consequences of introductions are sometimes great, and are directly related to global climate change, biodiversity AND release of genetically engineered organisms. Progress in invasion studies hinges on the following research trends: realization that species' ranges are naturally dynamic; recognition that colonist species and target communities cannot be studied independently, but that species-community interactions determine invasion success; increasingly quantitative tests of how species and habitat characteristics relate to invasibility and impact; recognition from paleobiological, experimental and modeling studies that history, chance and determinism together shape community invasibility.
Previous studies have concluded that southern ocean islands are anomalous because past glacial extent and current temperature apparently explain most variance in their species richness. Here, the relationships between physical variables and species richness of vascular plants, insects, land and seabirds, and mammals were reexamined for these islands. Indigenous and introduced species were distinguished, and relationships between the latter and human occupancy variables were investigated. Most variance in indigenous species richness was explained by combinations of area and temperature (56%)-vascular plants; distance (nearest continent) and vascular plant species richness (75%)-insects; area and chlorophyll concentration (65%)-seabirds; and indigenous insect species richness and age (73%)-land birds. Indigenous insects and plants, along with distance (closest continent), explained most variance (70%) in introduced land bird species richness. A combination of area and temperature explained most variance in species richness of introduced vascular plants (73%), insects (69%), and mammals (69%). However, there was a strong relationship between area and number of human occupants. This suggested that larger islands attract more human occupants, increasing the risk of propagule transfer, while temperature increases the chance of propagule establishment. Consequently, human activities on these islands should be regulated more tightly.
In a California riparian system, the most diverse natural assemblages are the most invaded by exotic plants. A direct in situ
manipulation of local diversity and a seed addition experiment showed that these patterns emerge despite the intrinsic negative
effects of diversity on invasions. The results suggest that species loss at small scales may reduce invasion resistance. At
community-wide scales, the overwhelming effects of ecological factors spatially covarying with diversity, such as propagule
supply, make the most diverse communities most likely to be invaded.
Predicting which species are probable invaders has been a long-standing goal of ecologists, but only recently have quantitative methods been used to achieve such a goal. Although restricted to few taxa, these studies reveal clear relationships between the characteristics of releases and the species involved, and the successful establishment and spread of invaders. For example, the probability of bird establishment increases with the number of individuals released and the number of release events. Also, the probability of plant invasiveness increases if the species has a history of invasion and reproduces vegetatively. These promising quantitative approaches should be more widely applied to allow us to predict patterns of invading species more successfully.
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880 during the initial stages of this work. T. Light was supported by an EPA STAR fellowship during the initial stages of this work
- Invasions In
- California Watersheds
- Center Project
INVASIONS IN CALIFORNIA WATERSHEDS
sources Center Project UCAL-WRC-W-880 during the initial
stages of this work. T. Light was supported by an EPA STAR
fellowship during the initial stages of this work.
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