From individuals to populations: the direct and indirect effects of predation on waterfowl nest success
No abstract available at this time
Thesis↗
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Predator of nesting waterbirds in an urban environment. Final Report
No abstract available at this time
Report↗
A review of sodium monofluoroacetate (compound 1080); its properties, toxicology, and use in predator and rodent control
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Special Scientific Report - Wildlife↗
Relative reproductive phenology and synchrony affect neonate survival in a nonprecocial ungulate
Degree of reproductive synchronization in prey is hypothesized as a predator defense strategy reducing prey risk via predator satiation or predator avoidance. Species with precocial young, especially those exposed to specialist predators, should be highly synchronous to satiate predators (predator satiation hypothesis), while prey with nonprecocial (i.e. altricial) young, especially those exposed to generalist predators, should become relatively asynchronous to avoid predator detection (predator avoidance hypothesis). The white-tailed deer Odocoileus virginianus in North America is an example of a nonprecocial ungulate that uses the hider strategy early in life; its primary predator (coyote; Canis latrans ) is a generalist, making white-tailed deer a good model species to test the predator avoidance hypothesis. We used birth dates and known fates of white-tailed deer neonates ( n = 1,032) across nine study sites varying in relative synchrony and predator assemblages to test the predator avoidance hypothesis. We predicted that relative birthing asynchrony of the population would increase relative survival at the population level; therefore, at the individual scale, neonate birth date nearer to mean birthing date in a respective population would not influence individual survival. Coyotes were responsible for the majority of predation events, and survival of those neonates increased the closer the individual was born to peak birthing season in each respective population. Also, at the population level, reproductive asynchronization negatively affected survival. Contrary to the predator avoidance hypothesis, our data indicate patterns in neonate survival for white-tailed deer better support the predator satiation hypothesis at the individual and population level. Additionally, coyotes may present a selective force great enough to shift reproductive synchrony such that predator satiation may become a feasible defense strategy for neonates at local spatial scales. Our results indicate that synchronizing reproduction may still be the most effective strategy to reduce individual predation risk from generalist predators, particularly when the window of heightened resource availability to the prey is narrow.
Alabama, Louisiana, Michigan, North Carolina, Penn↗
Antipredator responses by native mosquitofish to non-native cichlids: An examination of the role of prey naiveté
The strong impact of non-native predators in aquatic systems is thought to relate to the evolutionary naiveté of prey. Due to isolation and limited dispersal, this naiveté may be relatively high in freshwater systems. In this study, we tested this notion by examining the antipredator response of native mosquitofish, Gambusia holbrooki, to two non-native predators found in the Everglades, the African jewelfish, Hemichromis letourneuxi, and the Mayan cichlid, Cichlasoma urophthalmus . We manipulated prey naiveté by using two mosquitofish populations that varied in their experience with the recent invader, the African jewelfish, but had similar levels of experience with the longer-established Mayan cichlid. Specifically, we tested these predictions: (1) predator hunting modes differed between the two predators, (2) predation rates would be higher by the novel jewelfish predator, (3) particularly on the naive population living where jewelfish have not invaded yet, (4) antipredator responses would be stronger to Mayan cichlids due to greater experience and weaker and/or ineffective to jewelfish, and (5) especially weakest by the naive population. We assayed prey and predator behavior, and prey mortality in lab aquaria where both predators and prey were free-ranging. Predator hunting modes and habitat domains differed, with jewelfish being more active search predators that used slightly higher parts of the water column and less of the habitat structure relative to Mayan cichlids. In disagreement with our predictions, predation rates were similar between the two predators, antipredator responses were stronger to African jewelfish (except for predator inspections), and there was no difference in response between jewelfish-savvy and jewelfish-naive populations. These results suggest that despite the novelty of introduced predators, prey may be able to respond appropriately if non-native predator archetypes are similar enough to those of native predators, if prey rely on general antipredator responses or predation cues, and/or show neophobic responses.
Everglades↗
Match or mismatch: The influence of phenology on size-dependent life history and divergence in population structure
1. In gape-limited predators, body size asymmetries determine the outcome of predator-prey interactions. Due to ontogenetic changes in body size, the intensity of intra- and interspecific interactions may change rapidly between the match situation of a predator-prey system and the mismatch situation in which competition, including competition with the prey, dominates. 2. Based on a physiologically structured population model using the European perch (Perca fluviatilis), analysis was performed on how prey density (bream, Abramis brama), initial size differences in the young-of-the-year (YOY) age cohort of the predator, and phenology (time-gap in hatching of predator and prey) influence the size structure of the predator cohort. 3. In relation to the seasonality of reproduction, the match situation of the predator-prey system occurred when perch hatched earlier than bream and when no gape-size limitations existed, leading to decreased size divergence in the predator age cohort. Decreased size divergence was also found when bream hatched much earlier than perch, preventing perch predation on bream occurring, which, in turn, increased the competitive interaction of the perch with bream for the common prey, zooplankton; i.e. the mismatch situation in which also the mean size of the age cohort of the predator decreased. 4. In between the total match and the mismatch , however, only the largest individuals of the perch age cohort were able to prey on the bream, while smaller conspecifics got trapped in competition with each other and with bream for zooplankton, leading to enlarged differences in growth that increased size divergence. 5. The modelling results were combined with 7 years of field data in a lake, where large differences in the length-frequency distribution of YOY perch were observed after their first summer. These field data corroborate that phenology and prey density per predator are important mechanisms in determining size differences within theYOYage cohort of the predator. 6. The results demonstrate that the switch between competitive interactions and a predator-prey relationship depended on phenology . This resulted in pronounced size differences in the YOY age cohort, which had far-reaching consequences for the entire predator population.
Journal of Animal Ecology↗
Fish behavior and abundance monitoring near a floating surface collector in North Fork Reservoir, Clackamas River, Oregon, using multi-beam acoustic imaging sonar
An imaging sonar was used to assess the behavior and abundance of fish sized the same as salmonid smolt and bull trout ( Salvelinus confluentus ) at the entrance to the juvenile fish floating surface collector (FSC) at North Fork Reservoir, Oregon. The purpose of the FSC is to collect downriver migrating juvenile salmonids (Chinook salmon [ Oncorhynchus tshawytscha ], Coho salmon [ Oncorhynchus kisutch ], and steelhead [ Oncorhynchus mykiss ]) at the North Fork Dam and to safely route them around the hydroelectric projects. The objective of the imaging sonar component of this study was to assess the behaviors of both smolt and predator-size fish (smolt [60–250 millimeter] and predator 350–650 [millimeter]) observed near the FSC and to determine if the presence of predator-size fish influenced the abundance of smolt-size fish. An imaging sonar was deployed near the entrance to the FSC during the spring smolt out-migration period. The imaging sonar technology was an informative tool for assessing abundance and spatial and temporal behaviors of both smolt and predator-size fish near the entrance of the FSC. Both smolt and predator-size fish were regularly observed near the entrance, with greater abundances observed during day than during night. Behavioral differences were also observed between the two fish-size classes, with smolt-size fish traveling straighter with more directed movement, and predator-size fish generally showing more milling behavior. Additionally, the presence of predator-size fish may be effecting the abundance and direction of travel of smolt-size fish, as counts of smolt-size fish were reduced in conjunction with the presence of predator-size fish and a greater proportion of smolt-size fish were observed traveling away from the FSC when predator-size fish were present than when predator-size fish were absent. Results of modeling potential predator-prey interactions and influences indicated that both the number of juvenile fish tracks and photoperiod had the strongest effects on the number of predator fish tracks, with more predator-size fish tracks observed as the number of smolt-size fish tracks increased. Overall, the results indicate that predator-size fish are present near the entrance of the FSC, concomitant with smolt-size fish, and their abundances and behaviors indicate that they may be drawn to the entrance of the FSC because of the abundance of prey-sized fish found there.
Oregon↗
Do parents synchronise nest visits as an antipredator adaptation in birds of New Zealand and Tasmania?
Birds with altricial offspring need to feed them regularly, but each feeding visit risks drawing attention to the nest and revealing its location to potential predators. Synchronisation of visits by both parents has been suggested as a behavioural adaptation to reduce the risk of nest predation. Under this hypothesis, higher risk of nest predation favours greater synchrony of parental feeding visits. We investigated this prediction over three timescales using nestling provisioning data from 25 passerine species in Tasmania and New Zealand. We estimated the extent to which parents actively synchronised their visits to the nest by comparing observed patterns of synchrony with those expected to occur at random. We found that in general, species did not synchronise visits more often than expected by chance. Species varied in the tendency to synchronise visits, but this variation was not explained by likely predation pressure in the distant evolutionary past: New Zealand endemic species, which evolved in the absence of mammalian nest predators, synchronised their visits as often as species which evolved with more diverse predatory guilds. Nest predation risk has increased over time in New Zealand due to introduced predators, but synchrony in visits also was not explained by manipulated predation risk: visit synchrony was equivalent between a predator-removal site and a site where predators remained. However, within one New Zealand species, visit synchrony was higher for mainland populations, which have been exposed to predatory mammals for c .800 years, than for a population on an offshore island to which predatory mammals were never introduced. We conclude that breeding birds may have some capacity to adapt the synchrony with which they provision over short evolutionary timescales. However, the lack of synchrony in most species suggests that either asynchrony provides benefits that outweigh the greater risk of predation, or synchrony incurs costs not compensated by reduced predation.
Tasmania↗
Assessing effects of nonnative crayfish on mosquito survival
Introductions of nonnative predators often reduce biodiversity and affect natural predator–prey relationships and may increase the abundance of potential disease vectors (e.g., mosquitoes) indirectly through competition or predation cascades. The Santa Monica Mountains (California, U.S.A.), situated in a global biodiversity hotspot, is an area of conservation concern due to climate change, urbanization, and the introduction of nonnative species. We examined the effect of nonnative crayfish (Procambarus clarkii) on an existing native predator, dragonfly nymphs (Aeshna sp.), and their mosquito larvae (Anopheles sp.) prey. We used laboratory experiments to compare the predation efficiency of both predators, separately and together, and field data on counts of dragonfly nymphs and mosquito larvae sampled from 13 local streams. We predicted a lower predation efficiency of crayfish compared with native dragonfly nymphs and a reduced predation efficiency of dragonfly nymphs in the presence of crayfish. Dragonfly nymphs were an order of magnitude more efficient predators than crayfish, and dragonfly nymph predation efficiency was reduced in the presence of crayfish. Field count data showed that populations of dragonfly nymphs and mosquito larvae were strongly correlated with crayfish presence in streams, such that sites with crayfish tended to have fewer dragonfly nymphs and more mosquito larvae. Under natural conditions, it is likely that crayfish reduce the abundance of dragonfly nymphs and their predation efficiency and thereby, directly and indirectly, lead to higher mosquito populations and a loss of ecosystem services related to disease vector control.
California↗
Development and corroboration of a bioenergetics model for northern pikeminnow ( Ptychocheilus oregonensis ) feeding on juvenile salmonids in the Columbia River
A bioenergetics model was developed and corroborated for northern pikeminnow Ptychocheilus oregonensis , an important predator on juvenile salmonids in the Pacific Northwest. Predictions of modeled predation rate on salmonids were compared with field data from three areas of John Day Reservoir (Columbia River). To make bioenergetics model estimates of predation rate, three methods were used to approximate the change in mass of average predators during 30-d growth periods: observed change in mass between the first and the second month, predicted change in mass calculated with seasonal growth rates, and predicted change in mass based on an annual growth model. For all reservoir areas combined, bioenergetics model predictions of predation on salmon were 19% lower than field estimates based on observed masses, 45% lower than estimates based on seasonal growth rates, and 15% lower than estimates based on the annual growth model. For each growth approach, the largest differences in field-versus-model predation occurred at the midreservoir area (-84% to -67% difference). Model predictions of the rate of predation on salmonids were examined for sensitivity to parameter variation, swimming speed, sampling bias caused by gear selectivity, and asymmetric size distributions of predators. The specific daily growth rate of northern pikeminnow predicted by the model was highest in July and October and decreased during August. The bioenergetics model for northern pikeminnow performed well compared with models for other fish species that have been tested with field data. This model should be a useful tool for evaluating management actions such as predator removal, examining the influence of temperature on predation rates, and exploring interactions between predators in the Columbia River basin.
Oregon↗
A bioenergetics modeling evaluation of top-down control of ruffe in the St. Louis River, western Lake Superior
Ruffe ( Gymnocephalus cernuus ), were accidentally introduced into the St. Louis River estuary, western Lake Superior, in the mid 1980s and it was feared that they might affect native fish through predation on eggs and competition for forage and habitat. In an effort to control the abundance of ruffe and limit dispersal, a top-down control strategy using predators was implemented in 1989. We used bioenergetics modeling to examine the efficacy of top-down control in the St. Louis River from 1991 to 1994. Five predators--northern pike ( Esox lucius ), walleye ( Stizostedion vitreum vitreum ), smallmouth bass ( Micropterus dolomieui ), brown bullhead ( Ictalurus nebulosus ), and yellow perch ( Perca flavescens )--were modeled to determine their consumption of ruffe and four other native prey species-spottail shiner ( Notropis hudsonius ), emerald shiner ( Notropis atherinoides ), yellow perch ( Perca flavescens ), and black crappie ( Pomoxis nigromaculatus ). Although predators ate as much as 47% of the ruffe biomass in 1 year, they were not able to halt the increase in ruffe abundance. The St. Louis River is an open system that allows predators to move freely out of the system, and the biomass of managed predators did not increase. A selectivity index showed all five predators selected the native prey and avoided ruffe. The St. Louis River has several predator and prey species creating many complex predator-prey interactions; and top-down control of ruffe by the predators examined in this study did not occur.
Journal of Great Lakes Research↗
Feedbacks between community assembly and habitat selection shape variation in local colonization
1. Non-consumptive effects of predators are increasingly recognized as important drivers of community assembly and structure. Specifically, habitat selection responses to top predators during colonization and oviposition can lead to large differences in aquatic community structure, composition and diversity. 2. These differences among communities due to predators may develop as communities assemble, potentially altering the relative quality of predator vs. predator-free habitats through time. If so, community assembly would be expected to modify the subsequent behavioural responses of colonists to habitats containing top predators. Here, we test this hypothesis by manipulating community assembly and the presence of fish in experimental ponds and measuring their independent and combined effects on patterns of colonization by insects and amphibians. 3. Assembly modified habitat selection of dytscid beetles and hylid frogs by decreasing or even reversing avoidance of pools containing blue-spotted sunfish (Enneacanthus gloriosus). However, not all habitat selection responses to fish depended on assembly history. Hydrophilid beetles and mosquitoes avoided fish while chironomids were attracted to fish pools, regardless of assembly history. 4. Our results show that community assembly causes taxa-dependent feedbacks that can modify avoidance of habitats containing a top predator. Thus, non-consumptive effects of a top predator on community structure change as communities assemble and effects of competitors and other predators combine with the direct effects of top predators to shape colonization. 5. This work reinforces the importance of habitat selection for community assembly in aquatic systems, while illustrating the range of factors that may influence colonization rates and resulting community structure. Directly manipulating communities both during colonization and post-colonization is critical for elucidating how sequential processes interact to shape communities.
Journal of Animal Ecology↗
Snake River fall Chinook salmon life history investigations, 1/1/2012 - 12/31/2012: Annual report 2002-032-00
Executive Summary a. Fish Population RM&E This annual report describes the data collected and analyses conducted during calendar years 2012-2013 by staff of project 20023200. The USGS contributed only to the predation research and reservoir invertebrate work described in this report and the presentation of their results is consistent with USGS policy guidelines. The USGS is not responsible for the content provided by other contributing authors. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. The main goal of this project is to better understand juvenile Snake River fall Chinook salmon life history diversity and the factors that influence it. This is called for in RPA 55.4 “Investigate key characteristics of Snake River fall Chinook salmon early life history.” We 3 investigated the importance of estuary entry and rearing to various Snake River fall Chinook salmon life histories. Otoliths were used to examine differences in estuary use between subyearlings and yearlings, and to determine natal habitats, rearing habitats, and overwintering habitat for returning adults. Estuary growth was best explained by estuary residence time and natal location. b. Predation and Invasive Species Management RM&E We investigated the extent of smallmouth bass predation on juvenile fall Chinook salmon in Lower Granite Reservoir as called for in the Fish and Wildlife Program, “The federal action agencies should work cooperatively with NOAA Fisheries, states, tribes, and the Council to review, evaluate, develop, and implement strategies to reduce non-native piscivorous predation on salmon and steelhead, especially by smallmouth bass, channel catfish, and walleye” (Page 52). Smallmouth bass stomach contents were collected and analyzed for the presence of juvenile salmon. Smallmouth bass abundance was estimated with mark-recapture techniques, and salmon consumption by bass was expanded based on bass abundance to determine the annual loss of juvenile fall Chinook salmon for the study period and area. The estimated loss of juvenile fall Chinook salmon to predation in Lower Granite Reservoir exceeded 109,000 fish in 2012. This information could be used to adaptively formulate better hatchery release strategies to reduce the effects of predation. Obtaining better estimates of smallmouth bass abundance and distribution in future years would reduce the uncertainty of estimates. This study will be completed by 2017. We also examined the effects of various field temperature scenarios resulting from summer flow augmentation on juvenile fall Chinook salmon susceptibility to smallmouth bass predation in laboratory trials. Predation susceptibility of juvenile salmon acclimated at cool temperatures (10°C) was highest when exposed to predators at 24°C. These results indicate that predation susceptibility may be higher when a relatively large temperature difference exists between the Clearwater and Snake rivers; that is, when cool water flow augmentation occurs in summer. Finally, we examined the role of different invasive invertebrates in lower Snake River reservoir food webs that are food, or competitors for food, for juvenile fall Chinook salmon. The Siberian prawn, a relatively new invader, is relatively abundant but its role on the food web is largely unexplored. Prawns are successfully reproducing and their diet is 81% Neomysis (an invasive opossum shrimp) which is heavily used at times by juvenile salmon for food. Neomysis has become very abundant in lower Snake River reservoirs in recent years and may be a profitable food item for many fish species.
Oregon, Washington↗
Interactions between striped bass and other gamefish in reservoirs
Competitive interactions among reservoir fishes may be pronounced because fish assemblages in these artificial environments have had little time to develop niche-partitioning strategies that alleviate negative interspecific interactions. Such interactions may at times have been intensified by introductions of predators such as striped bass Morone saxatilis , introduced to create additional fisheries and control pelagic clupeids. Possible interactions between existing fish assemblages and striped bass include predation and competition. While there is a perception among angler groups that predation by striped bass on co-existing game fish is significant, most studies have reported little or no predation on game fish my striped bass and have considered predation rare and inconsequential. Moreover, predation that occurs will likely be compensatory and fail to reduce overall game fish survival. Any indirect effect of striped bass predation by restricting prey-sized game fish to limited refuge sites remains unknown. Exploitative competition may be more common. Although infrequently, introduced striped bass have depleted prey resources shared with other piscivores, particularly when stocking rates have been high, when there is a high rate of natural reproduction, or when prey supply has plunged in response to environmental fluxes. Fluctuation in prey supply, associated with ordinary environmental variability, and associated time lages in prey supply and predator demand, preclude adjusting predator densities to exactly balance demand with supply. The frequency of low supply-demand rations varies across systems and exhibits seasonal trends. Nevertheless, chronic supply-demand imbalances are manageable where the predator assemblage is at least partially controlled through stocking, harvest regulations, or both. Because of the poor state of knowledge concerning the parameters defining balance and because uncontrollable annual fluctuations preclude exact management of alternating prey levels, we suggest adjusting stocking to manage demand to that it equals the median historical prey supply. Simulating the removal of striped bass and predicting the aftermath may be the most cost-efficient way to provide decision support for stakeholders involved in determining if a striped bass stocking program is beneficial to most users.
American Fisheries Society Symposium↗
Snake River Fall Chinook Salmon life history investigations
Predation by nonnative fishes is one factor that has been implicated in the decline of juvenile salmonids in the Pacific Northwest. Impoundment of much of the Snake and Columbia rivers has altered food webs and created habitat favorable for species such as Smallmouth Bass Micropterus dolomieu . Smallmouth Bass are common throughout the Columbia River basin and have become the most abundant predator in lower Snake River reservoirs (Zimmerman and Parker 1995). This is a concern for Snake River Fall Chinook Salmon Oncorhynchus tshawytscha (hereafter, subyearlings) that may be particularly vulnerable due to their relatively small size and because their main-stem rearing habitats often overlap or are in close proximity to habitats used by Smallmouth Bass (Curet 1993; Tabor et al. 1993). Concern over juvenile salmon predation spawned a number of large-scale studies to quantify its effect in the late 1980s, 1990s, and early 2000s (Poe et al. 1991; Rieman et al. 1991; Vigg et al. 1991; Fritts and Pearsons 2004; Naughton et al. 2004). Smallmouth Bass predation represented 9% of total salmon consumption by predatory fishes in John Day Reservoir, Columbia River, from 1983 through 1986 (Rieman et al. 1991). In transitional habitat between the Hanford Reach of the Columbia River and McNary Reservoir, juvenile salmon (presumably subyearlings) were found in 65% of Smallmouth Bass (>200 mm) stomachs and comprised 59% of the diet by weight (Tabor et al. 1993). Within Lower Granite Reservoir on the Snake River, Naughton et al. (2004) showed that monthly consumption (based on weight) ranged from 5% in the upper reaches of the reservoir to 11% in the forebay. However, studies in the Snake River were conducted soon after Endangered Species Act (ESA) listing of Snake River Fall Chinook Salmon (NMFS 1992). During this time, Fall Chinook Salmon abundance was at an historic low, which may explain why consumption rates were relatively low compared to those from studies conducted in the Columbia and Yakima rivers where abundance was higher (e.g., Tabor et al. 1993; Fritts and Pearsons 2004). We speculate that predation on subyearlings by Smallmouth Bass in the Snake River may have increased in recent years for several reasons. Since their ESA listing, recovery measures implemented for Snake River Fall Chinook salmon have resulted in a large increase in the juvenile population (Connor et al. 2013). Considering that subyearlings probably now make up a larger portion of the forage fish population, it is plausible they should make up a large portion of Smallmouth Bass diets. Second, migrating subyearlings delay downstream movement in the transition zones of the Clearwater River and Snake River for varying lengths of time (Tiffan et al. 2010), which increases their exposure and vulnerability to predators. Spatial overlap in locations of Smallmouth Bass and subyearlings that died during migration provides support for this (Tiffan et al. 2010). Finally, the later outmigration of subyearlings from the Clearwater River results in their presence in Lower Granite Reservoir during the warmest summer months when predation rates of Smallmouth Bass should be highest. In 2016, we focused our efforts on Smallmouth Bass predation in Lower Granite Reservoir downstream of the transition zones and the confluence area where we worked during 2012–2015. Similar to past years, our first objective was to quantify Smallmouth Bass consumption rates of subyearlings, determine relative bass abundance, and describe bass diets. In addition, Tiffan et al. (2016a) posited that predation risk to subyearlings may be higher in shoreline habitats that are more suitable for Smallmouth Bass and lower in shoreline habitats that are more suitable for subyearlings. To test this hypothesis, our second objective examines the relationship between Smallmouth Bass predation of subyearlings and habitat suitability.
Idaho, Washington↗
Identifying recruitment sources across trophic levels in a large river food web
Assemblages are connected through the movement of physical and biological resources including recruits. Identifying recruitment sources for predators and their prey could help us understand how assemblages use connectivity across multiple trophic levels and whether predator and prey recruitment is coupled. Recruitment sources of organisms across multiple trophic levels can be quantified by trace element analysis of stomach contents. We used trace element analysis of otoliths to determine recruitment contributions from tributaries of predatory largemouth bass ( Micropterus salmoides ) and bowfin ( Amia calva ) and their consumed prey collected from Pools 4, 8, and 13 of the Upper Mississippi River. We used laser ablation inductively coupled mass spectrometry to quantify strontium:calcium of the core of each otolith and classified each fish to a natal origin (i.e., tributary or potential resident). We compared patterns of natal origin across study reaches, collection years, and species and with previously published origins of independently sampled prey fish. Predator and prey assemblages across all study reaches recruited from tributaries. More prey (44%) than predators (17%) recruited from tributaries. Of fishes originating from tributaries, individuals recruited from various rivers including the large Minnesota and Wisconsin Rivers and several small tributaries. Patterns in natal origin were similar among predators and prey families and among reaches, across sampling years, and between consumed prey and independently sampled prey. Tributaries consistently contributed recruits to both prey and predator fishes, leading to a coupling of predator and prey recruitment sources across space and time. Predators directly and indirectly used tributaries for recruitment and persistence through their own and their prey's recruitment. We further highlighted the utility of using consumed prey to simultaneously study the ecology of prey and predator assemblages, thereby reducing research sampling needs.
Illinois, Iowa, Minnesota, Wisconsin↗
Effects of multiple nonnative fish on an imperiled cyprinid, Hornyhead Chub
Nonnative fish can have substantial negative effects on the abundance and distribution of native fishes through predation and competition. Nonnative predators are of particular interest because they represent novel threats to native prey species that are not adapted to their presence. Prey species with limited distributions or population sizes may be particularly vulnerable to the effects of nonnative predators. In the Laramie River, four nonnative predators—Brown Trout Salmo trutta , Rainbow Trout Oncorhynchus mykiss , Brook Trout Salvelinus fontinalis, and Smallmouth Bass Micropterus dolomieu are present along with a state‐imperiled population of Hornyhead Chub Nocomis biguttatus . The abundance of Hornyhead Chub has declined with increasing abundance of nonnative predators, with the probability of occurrence of Hornyhead Chub dropping drastically when Smallmouth Bass were present. All four nonnative species preyed on native cyprinids, but Smallmouth Bass relied most heavily on fish as a prey item. Isotopic niche overlap occurred between Hornyhead Chub and all of the nonnative predator species. Our results demonstrate that nonnative predators have the potential to negatively affect the abundance and distribution of Hornyhead Chub through the mechanisms of predation and competition, and predator identity is important in determining the extent of effects. Smallmouth Bass are a greater concern than nonnative salmonids because of their more piscivorous behavior, and their recent upstream expansion may be limiting the downstream distribution of Hornyhead Chub in the Laramie River.
Wyoming↗
Kelp forest ecosystems: Biodiversity, stability, resilience and future
Kelp forests are phyletically diverse, structurally complex and highly productive components of coldwater rocky marine coastlines. This paper reviews the conditions in which kelp forests develop globally and where, why and at what rate they become deforested. The ecology and long archaeological history of kelp forests are examined through case studies from southern California, the Aleutian Islands and the western North Atlantic, well-studied locations that represent the widest possible range in kelp forest biodiversity. Global distribution of kelp forests is physiologically constrained by light at high latitudes and by nutrients, warm temperatures and other macrophytes at low latitudes. Within mid-latitude belts (roughly 40–60° latitude in both hemispheres) well-developed kelp forests are most threatened by herbivory, usually from sea urchins. Overfishing and extirpation of highly valued vertebrate apex predators often triggered herbivore population increases, leading to widespread kelp deforestation. Such deforestations have the most profound and lasting impacts on species-depauperate systems, such as those in Alaska and the western North Atlantic. Globally urchin-induced deforestation has been increasing over the past 2–3 decades. Continued fishing down of coastal food webs has resulted in shifting harvesting targets from apex predators to their invertebrate prey, including kelp-grazing herbivores. The recent global expansion of sea urchin harvesting has led to the widespread extirpation of this herbivore, and kelp forests have returned in some locations but, for the first time, these forests are devoid of vertebrate apex predators. In the western North Atlantic, large predatory crabs have recently filled this void and they have become the new apex predator in this system. Similar shifts from fish- to crab-dominance may have occurred in coastal zones of the United Kingdom and Japan, where large predatory finfish were extirpated long ago. Three North American case studies of kelp forests were examined to determine their long history with humans and project the status of future kelp forests to the year 2025. Fishing impacts on kelp forest systems have been both profound and much longer in duration than previously thought. Archaeological data suggest that coastal peoples exploited kelp forest organisms for thousands of years, occasionally resulting in localized losses of apex predators, outbreaks of sea urchin populations and probably small-scale deforestation. Over the past two centuries, commercial exploitation for export led to the extirpation of sea urchin predators, such as the sea otter in the North Pacific and predatory fishes like the cod in the North Atlantic. The large-scale removal of predators for export markets increased sea urchin abundances and promoted the decline of kelp forests over vast areas. Despite southern California having one of the longest known associations with coastal kelp forests, widespread deforestation is rare. It is possible that functional redundancies among predators and herbivores make this most diverse system most stable. Such biodiverse kelp forests may also resist invasion from non-native species. In the species-depauperate western North Atlantic, introduced algal competitors carpet the benthos and threaten future kelp dominance. There, other non-native herbivores and predators have become established and dominant components of this system. Climate changes have had measurable impacts on kelp forest ecosystems and efforts to control the emission of greenhouse gasses should be a global priority. However, overfishing appears to be the greatest manageable threat to kelp forest ecosystems over the 2025 time horizon. Management should focus on minimizing fishing impacts and restoring populations of functionally important species in these systems.
Environmental Conservation↗