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At least 1,315 records · Page 73Linked to original sources
USGS2025

Effects of nest exclosure on nest and adult survival of piping plover (Charadrius melodus) in the lower Platte River System, Nebraska

Conservation of imperiled species often includes management strategies intended to improve specific vital rates. However, some management practices can have unforeseen consequences that negate the intended benefit. For example, nest exclosures are often used for ground-nesting avian species to reduce nest predation but may increase depredation of adults. Tradeoffs between nest survival and adult mortality of nest exclosures likely depend on local predator community dynamics. Therefore, investigations are most informative when assessed in specific settings. Piping Plovers ( Charadrius melodus , hereafter plovers) in the lower Platte River system, Nebraska, nest at off-river sandpit sites, which provide an additional study system and habitat to assess the context-dependent effects of nest exclosures. The Tern and Plover Conservation Partnership monitors plovers at off-river sites by monitoring nests, installing nest exclosures, and banding and resighting. Effects of nest exclosures were tested on both nest survival, from 340 plover nests from 2008–2024, and weekly within-season apparent survival, from 71 breeding adults from 2011–2024. There was weak evidence that nest exclosures marginally improved nest survival but no evidence of an effect for within-season survival of breeding adults. Daily nest survival was slightly higher for exclosed nests (0.99, [85% CI = 0.98–0.99]) than unexclosed nests (0.98, [0.98–0.99]). Within-season apparent weekly survival for breeding plovers was 0.90 (95% CI = 0.83–0.93); cumulative survival over the breeding period was 0.51 (0.33–0.69). Nest exclosures may be used to increase nest survival at off-river sites with minimal threat to adult survival unless considerable concerns arise.

Nebraska↗
USGS2007

Restoration of waterbird habitats in Chesapeake Bay: Great expectations or Sisyphus revisited?

In the past half century, many waterbird populations in Chesapeake Bay have declined or shifted ranges, indicating major ecological changes have occurred. While many studies have focused on the problems associated with environmental degradation such as the losses of coastal wetlands and submerged vegetation, a number of restoration efforts have been launched in the past few decades to reverse the "sea of despair." Most pertinent to waterbirds, restoration of submerged aquatic vegetation (SAV) beds, tidal wetland restoration, oyster reef restoration, and island creation/restoration have benefited a number of species. State and federal agencies and non-government agencies have formed partnerships to spawn many projects ranging in size from less than 0.5 ha to ca. 1,000 ha. While most SAV, wetland, and oyster reef projects have struggled to different degrees over the past ten to twenty years with inconsistent methods, irregular monitoring, and unknown reasons for failures, recent improvements in techniques and application of adaptive management have been made. The large dredge-material island projects at Hart-Miller Island near Baltimore, Poplar Island west of Tilghman Island, Maryland, and Craney Island in Portsmouth, Virginia have provided large outdoor "laboratories" for wildlife, fishery, and wetland habitat creation. All three have proven to be important for nesting waterbirds and migrant shorebirds and waterfowl; however nesting populations at all three islands have been compromised to different degrees by predators. Restoration success for waterbirds and other natural resources depends on: (1) establishing realistic, quantifiable objectives and performance criteria, (2) continued monitoring and management (e.g., predator control), (3) targeted research to determine causality, and (4) careful evaluation under an adaptive management regime.

Waterbirds↗
USGS2010

Flexibility in nest-site choice and nesting success of Turdus rufiventris (Turdidae) in a montane forest in northwestern argentina

We studied the consequences of nest-site choice on nesting success under differing disturbance levels for the Rufous-bellied Thrush (Turdus rufiventris). We compared nest-site choice and nest success between a disturbed site and an undisturbed site in a montane subtropical forest in northwestern Argentina. We found no overall difference in daily predation rate (DPR) between the disturbed and undisturbed sites. However, DPR of nests on bromeliads was significantly lower at the microhabitat level than on other types of subtrates at the disturbed site. T. rufiventris used bromeliads for nesting more often than expected by chance at the disturbed site. DPR did not differ between substrates at the undisturbed site and T. rufiventris used all substrates according to their availability. Nests had higher predation at the disturbed site when DPR on non-bromeliad substrates was compared between disturbed and undisturbed sites. Nest fate was independent of nest height. Our results suggest T. rufiventris' flexibility in nest-site choice, as reflected by increased use of the safest sites, i.e., bromeliads, in the disturbed site compared to the undisturbed site, may allow this species to survive in an otherwise much riskier habitat. Our results illustrate how microhabitat-scale effects can mediate landscape scale effects. ?? 2010 by the Wilson Ornithological Society.

Wilson Journal of Ornithology↗
USGS2010

Breeding biology of the golden-faced Tyrannulet (Zimmerius chrysops) in venezuela

We present the first detailed information on the breeding biology of the Golden-faced Tyrannulet (Zimmerius chrysops). Information was gathered from 96 nests in Yacamb National Park, Venezuela during the 2002 to 2008 breeding seasons. The enclosed nest was similar to descriptions of nests of other species in the genus. Eggs were laid on alternate days with mean (?? SE) clutch size of 1.98 ?? 0.02 (n 45) and fresh weight of 1.616 ?? 0.020 g (n 48). Only the female incubated and the incubation period averaged 16.9 ?? 0.3 days (n 10). Nest attentiveness ( time on the nest) averaged 66.0 ?? 1.6 (n 40) and increased from early to mid- and late-incubation. Incubation behavior yielded an average 24-hr egg temperature of 34.88 ?? 0.45?? C (n 7 nests, 43 days). The nestling growth rate constant for body mass (k 0.285 ?? 0.011) was slow even for tropical tyrannids. The nestling period for nests where exact hatch and fledging days were observed ranged from 17 to 19 days with an average of 18.0 ?? 0. 2 days (n 9). Both females and males fed nestlings at a rate that increased over the nestling period with a mean of 4.41 ?? 0.65 trips/hr (n 10) during days 1 and 2 after hatching, and 14.93 ?? 2.36 trips/hr (n 6) at pin-break (days 1011). Daily predation rates were similar in egg-laying (0.052 ?? 0.025; n 76.5 exposure days) and incubation periods (0.068 ?? 0.010; n 575.5 exposure days), but were lower during the nestling period (0.039 ?? 0.010; n 377.0 exposure days). The total daily predation rate (0.057 ?? 0.007; n 989.0 exposure days) indicated only 12 of nests were successful. These breeding biology parameters for Z. chrysops differ substantially from other tyrant-flycatchers and temperate species, further highlighting the diversity within the Tyrannidae. ?? 2010 by the Wilson Ornithological Society.

Wilson Journal of Ornithology↗
USGS2019

Reproductive biology of Grey-breasted Wood-Wren (Henicorhina leucophrys): A comparative study of tropical and temperate wrens

We provide a detailed breeding biology account for the Grey-breasted Wood-Wren ( Henicorhina leucophrys ) and a comparison of the reproductive life history of tropical and temperate wrens using literature data. We conducted this study at Yacambú National Park in Venezuela from 2002 to 2008. Clutch size was 1.99 (SE 0.01) and fresh egg mass was 2.35 g (0.02). Females incubated the eggs for 19.74 d (0.37), and nestlings left nests at 17.37 d (0.18). Nest attentiveness (percent time spent on the nest) increased across the incubation period while brooding attentiveness decreased as nestlings aged. Brooding effort began with similar attentiveness as at the end of incubation. Food provisioning rate and feeding rate per nestling increased as nestlings aged. Growth rates ( K ) based on mass, tarsus, and wing chord were relatively slow at 0.375, 0.246, and 0.257, respectively. The nesting season extended from mid-March to late June for 7 years and the average nesting season length was 64.5 d (3.68) with a median of May 4. Nest success was 22%. Nest predation was the cause of 77% of nest failures with a total daily predation rate of 0.030 (0.002). Results obtained from the literature demonstrated that tropical wrens averaged smaller clutch sizes and longer incubation periods than relatives in the temperate region.

Yacambú National Park↗
USGS2019

Roost- and perch-site selection by Golden Eagles (Aquila chrysaetos) in eastern North America

Birds select critical resources to meet needs that vary in response to spatial, temporal, and individual variation. As an example, perch or roost sites may be at locations that provide protection from predators, mobbing, or inclement weather. Applied to large, soaring predators, this theory suggests that they may select perch and roost sites near food resources or at sites where environmental updrafts develop. To test these theories, we characterized selection of nonflight locations throughout the annual cycle for Golden Eagles ( Aquila chrysaetos ) in eastern North America. We determined factors associated with selection of perching (daytime) and roosting (nighttime) sites by eagles by comparing land cover and topographic characteristics of GPS telemetry locations for eagles (used) with random (available) locations. We separately assessed selection for perch and roost sites during each of 4 seasons (winter, summer, and spring and fall migration). Golden Eagles showed different selection patterns for perching by season and age. Throughout the year, eagles selected perch sites on steep slopes. The direction these slopes faced differed among seasons, with eagles selecting south-facing slopes in summer and east-facing slopes during migration. Adults showed greater preferences for broadleaf forests in summer and for ridges in fall. Patterns of perch-site use were consistent with selection for sites that provide thermal protection and access to thermal updrafts. We found few patterns of selection for roosting sites. Our analysis provides insight into decision-making by a longdistance migrant across its annual cycle and throughout its geographic range, and thus into how resource selection changes seasonally.

Wilson Journal of Ornithology↗
USGS2008

The human footprint in the west: a large-scale analysis of anthropogenic impacts.

Anthropogenic features such as urbanization, roads, and power lines, are increasing in western United States landscapes in response to rapidly growing human populations. However, their spatial effects have not been evaluated. Our goal was to model the human footprint across the western United States. We first delineated the actual area occupied by anthropogenic features, the physical effect area. Next, we developed the human footprint model based on the ecological effect area, the zone influenced by features beyond their physical presence, by combining seven input models: three models quantified top-down anthropogenic influences of synanthropic predators (avian predators, domestic dog and cat presence risk), and four models quantified bottom-up anthropogenic influences on habitat (invasion of exotic plants, human-caused fires, energy extraction, and anthropogenic wildland fragmentation). Using independent bird population data, we found bird abundance of four synanthropic species to correlate positively with human footprint intensity and negatively for three of the six species influenced by habitat fragmentation. We then evaluated the extent of the human footprint in relation to terrestrial (ecoregions) and aquatic systems (major rivers and lakes), regional management and conservation status, physical environment, and temporal changes in human actions. The physical effect area of anthropogenic features covered 13% of the western United States with agricultural land (9.8%) being most dominant. High-intensity human footprint areas (class 8 – 10) overlapped highly productive low-elevation private landholdings and covered 7% of the western United States compared to 48% for low-intensity areas (class 1 – 3), which were confined to low-productivity high-elevation federal landholdings. Areas within 1 km of rivers were more affected by the human footprint compared to lakes. Percentage human population growth was higher in low-intensity human footprint areas. The disproportional regional effects of the human footprint on landscapes in the western United States create a challenge to management of ecosystems and wildlife populations. Using footprint models, managers can plan land use actions, develop restoration scenarios, and identify areas of high conservation value at local landscapes within a regional context. Moreover, human footprint models serve as a tool to stratify landscapes for studies investigating floral and faunal response to human disturbance intensity gradients.

Ecological Applications↗
USGS2008

Mapping "old" versus "young" piñon-juniper stands with a predictive topo-climatic model in north-central New Mexico, USA

Piñon pine and juniper woodlands in the southwestern United States are often represented as an expanding and even invasive vegetation type, a legacy of historic grazing, and culpable in the degradation of western rangelands. A long-standing emphasis on forage production, in combination with recent hazard fuel concerns, has prompted a new era of woodland management with stated restoration objectives. Yet the extent and dynamics of piñon–juniper communities that predate intensive Euro-American settlement activities are poorly known or understood, while the intrinsic ecological, aesthetic, and economic values of old-growth woodlands are often overlooked. Historical changes in piñon–juniper stands include two related, but poorly differentiated processes: recent tree expansion into grass- or shrub-dominated (i.e., non-woodland) vegetation and thickening or infilling of savanna or mosaic woodlands predating settlement. Our work addresses the expansion pattern, modeling the occurrence of “older” savanna and woodland stands extant prior to 1850 in contrast to “younger” piñon–juniper growth of more recent, postsettlement origin. We present criteria in the form of a diagnostic key for distinguishing “older,” pre-Euro-American settlement piñon–juniper from “younger” (post-1850) stands and report results of predictive modeling and mapping efforts within a north-central New Mexico study area. Selected models suggest a primary role for soil moisture in the current distribution of “old” vs. “young” piñon–juniper stands. Presettlement era woodlands are shown to occupy a discrete ecological space, defined by the interaction of effective (seasonal) moisture with landform setting and fine-scale (soil/water) depositional patterns. “Older” stands are generally found at higher elevations or on skeletal soils in upland settings, while “younger” stands (often dominated by one-seed juniper, Juniperus monosperma ) are most common at lower elevations or in productive, depositional settings. Modeling at broad regional scales can enhance our general understanding of piñon–juniper ecology, while predictive mapping of local areas has potential to provide products useful for land management. Areas of the southwestern United States with strong monsoonal (summer moisture) patterns appear to have been the most susceptible to historical woodland expansion, but even here the great majority of extant piñon–juniper has presettlement origins (although widely thickened and infilled historically), and old-growth structure is not uncommon in appropriate upland settings.

Ecological Applications↗
USGS2010

A new parameterization for estimating co‐occurrence of interacting species

Models currently used to estimate patterns of species co‐occurrence while accounting for errors in detection of species can be difficult to fit when the effects of covariates on species occurrence probabilities are included. The source of the estimation problems is the particular parameterization used to specify species co‐occurrence probability. We develop a new parameterization for estimating patterns of co‐occurrence of interacting species that allows the effects of covariates to be specified quite naturally without estimation problems. In our model, the occurrence of one species is assumed to depend on the occurrence of another, but the occurrence of the second species is not assumed to depend on the presence of the first species. This pattern of co‐occurrence, wherein one species is dominant and the other is subordinate, can be produced by several types of ecological interactions (predator–prey, parasitism, and so on). A simulation study demonstrated that estimates of species occurrence probabilities were unbiased in samples of 50–100 locations and three surveys per location, provided species are easily detected (probability of detection ≥ 0.5). Higher sample sizes (>200 locations) are needed to achieve unbiasedness when species are more difficult to detect. An analysis of data from treefrog surveys in southern Florida indicated that the occurrence of Cuban treefrogs, an invasive predator species, was highest near the point of its introduction and declined with distance from that location. Sites occupied by Cuban treefrogs were 9.0 times less likely to contain green treefrogs and 15.7 times less likely to contain squirrel treefrogs compared to sites without Cuban treefrogs. The detection probabilities of native treefrog species did not depend on the presence of Cuban treefrogs, suggesting that the native treefrog species are naive to the introduced species.

Ecological Applications↗
USGS2001

Food webs including parasites, biomass, body sizes, and life stages for three California/Baja California estuaries

This data set presents food webs for three North American Pacific coast estuaries and a “Metaweb” composed of the species/stages compiled from all three estuaries. The webs have four noteworthy attributes: (1) parasites (infectious agents), (2) body-size information, (3) biomass information, and (4) ontogenetic stages of many animals with complex life cycles. The estuaries are Carpinteria Salt Marsh, California (CSM); Estero de Punta Banda, Baja California (EPB); and Bahía Falsa in Bahía San Quintín, Baja California (BSQ). Most data on species assemblages and parasitism were gathered via consistent sampling that acquired body size and biomass information for plants and animals larger than ∼1 mm, and for many infectious agents (mostly metazoan parasites, but also some microbes). We augmented this with information from additional published sources and by sampling unrepresented groups (e.g., plankton). We estimated free-living consumer–resource links primarily by extending a previously published version of the CSM web (which the current CSM web supplants) and determined most parasite consumer–resource links from direct observation. We recognize 21 possible link types including four general interactions: predators consuming prey, parasites consuming hosts, predators consuming parasites, and parasites consuming parasites. While generally resolved to the species level, we report stage-specific nodes for many animals with complex life cycles. We include additional biological information for each node, such as taxonomy, lifestyle (free-living, infectious, commensal, mutualist), mobility, and residency. The Metaweb includes 500 nodes, 314 species, and 11 270 links projected to be present given appropriate species' co-occurrences. Of these, 9247 links were present in one or more of the estuarine webs. The remaining 2023 links were not present in the estuaries but are included here because they may occur in other places or times. Initial analyses have examined and are examining the interrelationships among consumer strategy, body size, abundance, biomass, trophic level, life stages, and food-web structure and dynamics. Further use of these data may enable a more general exploration how infectious processes and parasites impact communities and ecosystems. Additionally, we present the data and metadata in a standardized format, attempting to provide a system-neutral template for future food-web assembly and publication.

Ecology↗
USGS1997

Conditions for the return and simulation of the recovery of burrowing mayflies in western Lake Erie

In the 1950s, burrowing mayflies, Hexagenia spp. ( H. limbata and H. rigida ), were virtually eliminated from the western basin of Lake Erie (a 3300 km 2 area) because of eutrophication and pollution. We develop and present a deterministic model for the recolonization of the western basin by Hexagenia to pre-1953 densities. The model was based on the logistic equation describing the population growth of Hexagenia and a presumed competitor, Chironomus (dipteran larvae). Other parameters (immigration, low oxygen, toxic sediments, competition with Chironomus, and fish predation) were then individually added to the logistic model to determine their effect at different growth rates. The logistic model alone predicts 10–41 yr for Hexagenia to recolonize western Lake Erie. Immigration reduced the recolonization time by 2–17 yr. One low-oxygen event during the first 20 yr increased recovery time by 5–17 yr. Contaminated sediments added 5–11 yr to the recolonization time. Competition with Chironomus added 8–19 yr to recovery. Fish predators added 4–47 yr to the time required for recolonization. The full model predicted 48–81 yr for Hexagenia to reach a carrying capacity of ≈350 nymphs/m 2 , or not until around the year 2038 if the model is started in 1990. The model was verified by changing model parameters to those present in 1970, beginning the model in 1970 and running it through 1990. Predicted densities overlapped almost completely with actual estimated densities of Hexagenia nymphs present in the western basin in Lake Erie in 1990. The model suggests that recovery of large aquatic ecosystems may lag substantially behind remediation efforts.

Michigan, Ohio, Ontario↗
USGS2014

Multi-trophic resilience of boreal lake ecosystems to forest fires

Fires are the major natural disturbance in the boreal forest, and their frequency and intensity will likely increase as the climate warms. Terrestrial nutrients released by fires may be transported to boreal lakes, stimulating increased primary productivity, which may radiate through multiple trophic levels. Using a before‐after‐control‐impact (BACI) design, with pre‐ and postfire data from burned and unburned areas, we examined effects of a natural fire across several trophic levels of boreal lakes, from nutrient and chlorophyll levels, to macroinvertebrates, to waterbirds. Concentrations of total nitrogen and phosphorus were not affected by the fire. Chlorophyll a levels were also unaffected, likely reflecting the stable nutrient concentrations. For aquatic invertebrates, we found that densities of three functional feeding groups did not respond to the fire (filterers, gatherers, scrapers), while two groups increased (shredders, predators). Amphipods accounted for 98% of shredder numbers, and we hypothesize that fire‐mediated habitat changes may have favored their generalist feeding and habitat ecology. This increase in amphipods may, in turn, have driven increased predator densities, as amphipods were the most numerous invertebrate in our lakes and are commonly taken as prey. Finally, abundance of waterbird young, which feed primarily on aquatic invertebrates, was not affected by the fire. Overall, ecosystems of our study lakes were largely resilient to forest fires, likely due to their high initial nutrient concentrations and small catchment sizes. Moreover, this resilience spanned multiple trophic levels, a significant result for ecologically similar boreal regions, especially given the high potential for increased fires with future climate change.

Alaska↗
USGS2014

Amphibians in the climate vise: loss and restoration of resilience of montane wetland ecosystems in the western US

Wetlands in the remote mountains of the western US have undergone two massive ecological “experiments” spanning the 20th century. Beginning in the late 1800s and expanding after World War II, fish and wildlife managers intentionally introduced millions of predatory trout (primarily Oncorhynchus spp) into fishless mountain ponds and lakes across the western states. These new top predators, which now occupy 95% of large mountain lakes, have limited the habitat distributions of native frogs, salamanders, and wetland invertebrates to smaller, more ephemeral ponds where trout do not survive. Now a second “experiment” – anthropogenic climate change – threatens to eliminate many of these ephemeral habitats and shorten wetland hydroperiods. Caught between climate-induced habitat loss and predation from introduced fish, native mountain lake fauna of the western US – especially amphibians – are at risk of extirpation. Targeted fish removals, guided by models of how wetlands will change under future climate scenarios, provide innovative strategies for restoring resilience of wetland ecosystems to climate change.

Western United States↗
USGS2015

Spatial complexity reduces interaction strengths in the meta-food web of a river floodplain mosaic

Theory states that both the spatial complexity of landscapes and the strength of interactions between consumers and their resources are important for maintaining biodiversity and the 'balance of nature.' Spatial complexity is hypothesized to promote biodiversity by reducing potential for competitive exclusion; whereas, models show weak trophic interactions can enhance stability and maintain biodiversity by dampening destabilizing oscillations associated with strong interactions. Here we show that spatial complexity can reduce the strength of consumer-resource interactions in natural food webs. By sequentially aggregating food webs of individual aquatic habitat patches across a floodplain mosaic, we found that increasing spatial complexity resulted in decreases in the strength of interactions between predators and prey, owing to a greater proportion of weak interactions and a reduced proportion of strong interactions in the meta-food web. The main mechanism behind this pattern was that some patches provided predation refugia for species which were often strongly preyed upon in other patches. If weak trophic interactions do indeed promote stability, then our findings may signal an additional mechanism by which complexity and stability are linked in nature. In turn, this may have implications for how the values of landscape complexity, and the costs of biophysical homogenization, are assessed.

Ecology↗
USGS2007

Comparative growth and consumption potential of rainbow trout and humpback chub in the Colorado River, Grand Canyon, Arizona, under different temperature scenarios

We used bioenergetics models for humpback chub, Gila cypha, and rainbow trout, Oncorhynchus mykiss, to examine how warmer water temperatures in the Colorado River, Grand Canyon, Arizona, through a proposed selective withdrawal system (SWS) at Glen Canyon Dam, would affect growth, consumption, and predation rates. Consumption by the rainbow trout population was at least 10 times higher than by the smaller humpback chub population. Water temperature increases of 6??C during autumn increased growth of humpback chub and likely increased their survival by reducing the time vulnerable to predation. Water temperature increases caused by drought in 2005 did not alter humpback chub growth as much as the SWS. Increased temperatures might cause changes to the invertebrate community and the distribution and abundance of other warmwater nonnative fishes. The implications on the entire aquatic community need to be considered before any management action that includes increasing water temperatures is implemented.

Southwestern Naturalist↗
USGS2023

Microhabitat use of native Santa Ana sucker and arroyo chub in an effluent-dominated southern California stream

A significant amount of the base flow of the Santa Ana River, located within California's arid Los Angeles metropolitan region, originates from two wastewater treatment facilities: the Rialto wastewater treatment facility and Rapid Infiltration and Extraction facility. The Santa Ana sucker ( Pantosteus santaanae , syn. Catostomus santaanae ) and arroyo chub ( Gila orcuttii ) are two native species listed in the Upper Santa Ana Habitat Conservation Plan, which aims to balance water supply needs with the ecological needs of native fauna. Consequently, an understanding of the habitat needs of these fishes will play a crucial role in achieving the goals outlined by the conservation plan. We used fish presence during snorkel surveys with habitat availability surveys to quantify habitat selection by both native fish species within a resource selection function analytical framework. We found that both species selected habitat near structures that could serve as refugia from potential predators. In addition, Santa Ana sucker selected habitats with high gravel and cobble substrate composition, presumably to fulfill complementary habitat needs such as foraging and spawning. Our results suggest that habitat alterations due to water management infrastructure and an increasing population size of nonnative predators may also affect native fish habitat selection in the Santa Ana River.

California↗
USGS2009

Trophic relationships of small nonnative fishes in a natural creek and several agricultural drains flowing into the Salton Sea, and their potential, effects on the endangered desert pupfish

This study was conducted to characterize trophic relationships of small nonnative fishes and to determine if predation by these fishes contributes to the decline of desert pupfish (Cyprinodon macularius), an endangered cyprinodont on the verge of extinction. We sampled 403 hybrid Mozambique tilapias (Oreochromis mossambica by O. urolepis), 107 redbelly tilapias (Tilapia zillii), 32 longjaw mudsuckers (Gillkhthys mirabilis), 182 western mosquitofish (Gambusia affinis), 222 sailfin mollies (Poecilia latipinna), 63 shortfin mollies (Poecilia mexicana), and 235 porthole livebearers (Poecilurpsis gracilis) from a natural creek and four agricultural drains during September 1999- December 2001. Evidence of piscivory was in gastrointestinal contents of 14 hybrid Mozambique tilapias, 3 redbelly tilapias, 10 longjaw mudsuckers, 8 western mosquitofish, 2 sailfin mollies, and 8 porthole livebearers. Although digestion often was too advanced for identification of fishes consumed by nonnative fishes, remains of desert pupfish were in gastrointestinal contents of a longjaw mudsucker. Our findings, along with Field evidence from other studies that inverse relationships exist between abundances of desert pupfish and nonnative species, are consistent with the hypothesis that predation by nonnative species is contributing to decline of desert pupfish. We suspect that competitive interactions with nonnative fishes might also adversely affect abundance of desert pupfish.

Southwestern Naturalist↗
USGS1997

Tadpole swimming performance and activity affected by acute exposure to sublethal levels of carbaryl

General activity and swimming performance (i.e., sprint speed and distance) of plains leopard frog tadpoles (Rana blairi) were examined after acute exposure to three sublethal concentrations of carbaryl (3.5, 5.0, and 7.2 mg/L). Both swimming performance and spontaneous swimming activity are important for carrying out life history functions (e.g., growth and development) and for escaping from predators. Measured tadpole activity diminished by nearly 90% at 3.5 mg/L carbaryl and completely ceased at 7.2 mg/L. Sprint speed and sprint distance also decreased significantly following exposure. Carbaryl affected both swimming performance and activity after just 24 h, suggesting that 24 h may be an adequate length of exposure to determine behavioral effects on tadpoles. Slight recovery of activity levels was noted at 24 and 48 h post-exposure; no recovery of swimming performance was observed. Reduction in activity and swimming performance may result in increased predation rates and, because activity is closely associated with feeding, may result in slowed growth leading to a failure to emerge before pond drying or an indirect reduction in adult fitness. Acute exposure to sublethal toxicants such as carbaryl may not only affect immediate survival of tadpoles but also impact critical life history functions and generate changes at the local population level.

Environmental Toxicology and Chemistry↗