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J.C. Trexler

Publications and source records attributed to J.C. Trexler.

15 recordsLinked to original sources
USGS2011

Using data from an encounter sampler to model fish dispersal

A method to estimate speed of free-ranging fishes using a passive sampling device is described and illustrated with data from the Everglades, U.S.A. Catch per unit effort (CPUE) from minnow traps embedded in drift fences was treated as an encounter rate and used to estimate speed, when combined with an independent estimate of density obtained by use of throw traps that enclose 1 m 2 of marsh habitat. Underwater video was used to evaluate capture efficiency and species-specific bias of minnow traps and two sampling studies were used to estimate trap saturation and diel-movement patterns; these results were used to optimize sampling and derive correction factors to adjust species-specific encounter rates for bias and capture efficiency. Sailfin mollies Poecilia latipinna displayed a high frequency of escape from traps, whereas eastern mosquitofish Gambusia holbrooki were most likely to avoid a trap once they encountered it; dollar sunfish Lepomis marginatus were least likely to avoid the trap once they encountered it or to escape once they were captured. Length of sampling and time of day affected CPUE; fishes generally had a very low retention rate over a 24 h sample time and only the Everglades pygmy sunfish Elassoma evergladei were commonly captured at night. Dispersal speed of fishes in the Florida Everglades, U.S.A., was shown to vary seasonally and among species, ranging from 0.05 to 0.15 m s -1 for small poeciliids and fundulids to 0.1 to 1.8 m s -1 for L. marginatus . Speed was generally highest late in the wet season and lowest in the dry season, possibly tied to dispersal behaviours linked to finding and remaining in dry-season refuges. These speed estimates can be used to estimate the diffusive movement rate, which is commonly employed in spatial ecological models.

Florida↗
USGS2008

Food web dynamics in a seasonally varying wetland

A spatially explicit model is developed to simulate the small fish community and its underlying food web, in the freshwater marshes of the Everglades. The community is simplified to a few small fish species feeding on periphyton and invertebrates. Other compartments are detritus, crayfish, and a piscivorous fish species. This unit food web model is applied to each of the 10,000 spatial cells on a 100 x 100 pixel landscape. Seasonal variation in water level is assumed and rules are assigned for fish movement in response to rising and falling water levels, which can cause many spatial cells to alternate between flooded and dry conditions. It is shown that temporal variations of water level on a spatially heterogeneous landscape can maintain at least three competing fish species. In addition, these environmental factors can strongly affect the temporal variation of the food web caused by top-down control from the piscivorous fish.

Mathematical Biosciences and Engineering↗
USGS2006

Spatial patterns of fish communities along two estuarine gradients in southern Florida

In tropical and subtropical estuaries, gradients of primary productivity and salinity are generally invoked to explain patterns in community structure and standing crops of fishes. We documented spatial and temporal patterns in fish community structure and standing crops along salinity and nutrient gradients in two subtropical drainages of Everglades National Park, USA. The Shark River drains into the Gulf of Mexico and experiences diurnal tides carrying relatively nutrient enriched waters, while Taylor River is more hydrologically isolated by the oligohaline Florida Bay and experiences no discernable lunar tides. We hypothesized that the more nutrient enriched system would support higher standing crops of fishes in its mangrove zone. We collected 50 species of fish from January 2000 to April 2004 at six sampling sites spanning fresh to brackish salinities in both the Shark and Taylor River drainages. Contrary to expectations, we observed lower standing crops and density of fishes in the more nutrient rich tidal mangrove forest of the Shark River than in the less nutrient rich mangrove habitats bordering the Taylor River. Tidal mangrove habitats in the Shark River were dominated by salt-tolerant fish and displayed lower species richness than mangrove communities in the Taylor River, which included more freshwater taxa and yielded relatively higher richness. These differences were maintained even after controlling for salinity at the time of sampling. Small-scale topographic relief differs between these two systems, possibly created by tidal action in the Shark River. We propose that this difference in topography limits movement of fishes from upstream marshes into the fringing mangrove forest in the Shark River system, but not the Taylor River system. Understanding the influence of habitat structure, including connectivity, on aquatic communities is important to anticipate effects of construction and operational alternatives associated with restoration of the Everglades ecosystem.

Florida↗
USGS2006

Fish community structure in freshwater karstic water bodies of the Sian Ka'an Reserve in the Yucatan peninsula, Mexico

We evaluated the relationship between limnetic characteristics and fish community structure (based on species richness, abundance and individual size) in contrasting but interconnected inland aquatic habitats of freshwater karstic wetlands in the Yucatan peninsula, Mexico. In the western hemisphere, freshwater karstic wetlands are found in south-eastern Mexico, northern Belize, western Cuba, Andros Island, Bahamas and the Everglades of southern Florida. Only in the Everglades have fish communities been well described. Karstic wetlands are typically oligotrophic because calcium carbonate binds phosphorus, making it relatively unavailable for plants. Fourteen permanent and seasonally flooded water bodies were sampled in both wet and dry seasons in Sian Ka'an Biosphere Reserve, in the Mexican state of Quintana Roo. Water systems were divided by morphology in four groups: cenotes with vegetation (CWV), cenotes without vegetation (CNV), wetlands (WTL), and temporal cenotes (TPC). Discriminant analysis based on physical characteristics such as turbidity, temperature, depth and oxygen confirmed that these habitats differed in characteristics known to influence fish communities. A sample-based rarefaction test showed that species richness was significantly different between water systems groups, showing that WTL and CWV had higher richness values than CNV and TPC. The most abundant fish families, Poeciliidae, Cichlidae and Characidae, differed significantly in average size among habitats and seasons. Seasonal and inter-annual variation, reflecting temporal variation in rainfall, strongly influenced the environmental differences between shallow and deep habitats, which could be linked to fish size and life cycles. Five new records of species were found for the reserve, and one new record for Quintana Roo state. ?? 2006 by Verlag Dr. Friedrich Pfeil.

Ichthyological Exploration of Freshwaters↗
USGS2005

Disturbance frequency and community structure in a twenty-five year intervention study

Models of community regulation commonly incorporate gradients of disturbance inversely related to the role of biotic interactions in regulating intermediate trophic levels. Higher trophic-level organisms are predicted to be more strongly limited by intermediate levels of disturbance than are the organisms they consume. We used a manipulation of the frequency of hydrological disturbance in an intervention analysis to examine its effects on small-fish communities in the Everglades, USA. From 1978 to 2002, we monitored fishes at one long-hydroperiod (average 350 days) and at one short-hydroperiod (average 259 days; monitoring started here in 1985) site. At a third site, managers intervened in 1985 to diminish the frequency and duration of marsh drying. By the late 1990s, the successional dynamics of density and relative abundance at the intervention site converged on those of the long-hydroperiod site. Community change was manifested over 3 to 5 years following a dry-down if a site remained inundated; the number of days since the most recent drying event and length of the preceding dry period were useful for predicting population dynamics. Community dissimilarity was positively correlated with the time since last dry. Community dynamics resulted from change in the relative abundance of three groups of species linked by life-history responses to drought. Drought frequency and intensity covaried in response to hydrological manipulation at the landscape scale; community-level successional dynamics converged on a relatively small range of species compositions when drought return-time extended beyond 4 years. The density of small fishes increased with diminution of drought frequency, consistent with disturbance-limited community structure; less-frequent drying than experienced in this study (i.e., longer return times) yields predator-dominated regulation of small-fish communities in some parts of the Everglades. ?? Springer-Verlag 2005.

Oecologia↗
USGS2005

Population dynamics of wetland fishes: Spatio-temporal patterns synchronized by hydrological disturbance?

1. Drought is a natural disturbance that can cause widespread mortality of aquatic organisms in wetlands. We hypothesized that seasonal drying of marsh surfaces (i.e. hydrological disturbance) shapes spatio-temporal patterns of fish populations. 2. We tested whether population dynamics of fishes were synchronized by hydrological disturbance (Moran effect) or distance separating study sites (dispersal). Spatio-temporal patterns were examined in local populations of five abundant species at 17 sites (sampled five times per year from 1996 to 2001) in a large oligotrophic wetland. 3. Fish densities differed significantly across spatio-temporal scales for all species. For all species except eastern mosquitofish (Gambusia holbrooki), a significant portion of spatio-temporal variation in density was attributed to drying events (used as a covariate). 4. We observed three patterns of response to hydrological disturbance. Densities of bluefin killifish (Lucania goodei), least killifish (Heterandria formosa), and golden top-minnow (Fundulus chrysotus) were usually lowest after a dry down and recovered slowly. Eastern mosquitofish showed no distinct response to marsh drying (i.e. they recovered quickly). Flagfish (Jordanella floridae) density was often highest after a dry down and then declined. Population growth after a dry down was often asymptotic for bluefin killifish and golden topminnow, with greatest asymptotic density and longest time to recovery at sites that dried infrequently. 5. Fish population dynamics were synchronized by hydrological disturbance (independent of distance) and distance separating study sites (independent of hydrological disturbance). Our ability to separate the relative importance of the Moran effect from dispersal was strengthened by a weak association between hydrological synchrony and distance among study sites. Dispersal was the primary mechanism for synchronous population dynamics of flagfish, whereas hydrological disturbance was the primary mechanism for synchronous population dynamics of the other species examined. 6. Species varied in the relative role of the Moran effect and dispersal in homogenizing their population dynamics, probably as a function of life history and ability to exploit dry-season refugia. ?? 2005 British Ecological Society.

Journal of Animal Ecology↗
USGS2005

Life history trade-offs and community dynamics of small fishes in a seasonally pulsed wetland

We used a one-dimensional, spatially explicit model to simulate the community of small fishes in the freshwater wetlands of southern Florida, USA. The seasonality of rainfall in these wetlands causes annual fluctuations in the amount of flooded area. We modeled fish populations that differed from each other only in efficiency of resource utilization and dispersal ability. The simulations showed that these trade-offs, along with the spatial and temporal variability of the environment, allow coexistence of several species competing exploitatively for a common resource type. This mechanism, while sharing some characteristics with other mechanisms proposed for coexistence of competing species, is novel in detail. Simulated fish densities resembled patterns observed in Everglades empirical data. Cells with hydroperiods less than 6 months accumulated negligible fish biomass. One unique model result was that, when multiple species coexisted, it was possible for one of the coexisting species to have both lower local resource utilization efficiency and lower dispersal ability than one of the other species. This counterintuitive result is a consequence of stronger effects of other competitors on the superior species. ?? 2005 NRC.

Conference Paper↗
USGS2005

Spatiotemporal patterns in community structure of macroinvertebrates inhabiting calcareous periphyton mats

Calcareous floating periphyton mats in the southern Everglades provide habitat for a diverse macroinvertebrate community that has not been well characterized. Our study described this community in an oligotrophic marsh, compared it with the macroinvertebrate community associated with adjacent epiphytic algae attached to macrophytes in the water column, and detected spatial patterns in density and community structure. The floating periphyton mat (floating mat) and epiphytic algae in the water column (submerged epiphyton) were sampled at 4 sites (???1 km apart) in northern Shark River Slough, Everglades National Park (ENP), in the early (July) and late (November) wet season. Two perpendicular 90-m transects were established at each site and ???100 samples were taken in a nested design. Sites were located in wet-prairie spikerush-dominated sloughs with similar water depths and emergent macrophyte communities. Floating mats were sampled by taking cores (6-cm diameter) that were sorted under magnification to enumerate infauna retained on a 250-??m-mesh sieve and with a maximum dimension >1 mm. Our results showed that floating mats provide habitat for a macroinvertebrate community with higher densities (no. animals/g ash-free dry mass) of Hyalella azteca, Dasyhelea spp., and Cladocera, and lower densities of Chironomidae and Planorbella spp. than communities associated with submerged epiphyton. Densities of the most common taxa increased 3x to 15x from early to late wet season, and community differences between the 2 habitat types became more pronounced. Floating-mat coverage and estimated floating-mat biomass increased 20 to 30%, and 30 to 110%, respectively, at most sites in the late wet season. Some intersite variation was observed in individual taxa, but no consistent spatial pattern in any taxon was detected at any scale (from 0.2 m to 3 km). Floating mats and their resident macroinvertebrate communities are important components in the Everglades food web. This community should be included in environmental monitoring programs because degradation and eventual loss of the calcareous periphyton mat is associated with P enrichment in this ecosystem. ?? 2005 by The North American Benthological Society.

Journal of the North American Benthological Societ↗
USGS2004

Community structure of fishes inhabiting aquatic refuges in a threatened Karst wetland and its implications for ecosystem management

We illustrate the importance of subsurface refuges for conservation of aquatic fauna with our studies of karstic wetlands in Everglades National Park, Florida, USA. Managers have proposed that water levels there should not fall more than 46 cm below ground level for more than 90 days annually. In four areas, 84% of solution holes were less than 46 cm deep and holes deeper than lm were rare (<3 km-2). Null-model analysis indicated no "structure" in the solution-hole fish communities early in the dry season, but that structure emerged as drying progressed. Native cyprinodontiforms were abundant in shallow solution holes that dry annually under current management, while predatory species (often non-native) tended to dominate deeper holes. Water quality was correlated with hole volume and with composition of late dry-season fish communities. Tremendous losses of fish biomass occurred when water levels fell below 46 cm from ground surface. Most native taxa were unlikely to survive in the deep refuges that held predatory non-native taxa. ?? 2003 Elsevier Ltd. All rights reserved.

Biological Conservation↗
USGS2002

Genetic diversity in a morphologically conservative invasive taxon: Multiple introductions of swamp eels to the southeastern United States

Genetic analysis of introduced populations, especially in morphologically conservative taxa, can clarify introduction histories, identify management units and source populations, provide a more realistic estimate of the frequency of successful invasion, and suggest strategies for preventing further introductions. In the last 7 years, populations of swamp eels, referred to the Asian genus Monopterus (Family Synbranchidae) on the basis of external morphology, have been discovered in aquatic habitats near Atlanta, Georgia; Tampa, Florida; North Miami, Florida; and most recently in close proximity to Everglades National Park in Homestead, Florida. Swamp eels are large predators capable of dispersal over land and have the potential to disrupt already threatened ecosystems. We analyzed mitochondrial DNA sequences from four known populations in the continental United States and samples from Malaysia, Indonesia, Vietnam, and two locations in China to determine introduction histories, source populations, genetic diversity, and relationships among populations. Our results indicate that there have been at least three independent introductions of genetically distinct forms. Introduced populations in close proximity (separated by <40 km) are genetically distinct. The level of sequence difference among introduced populations reaches levels seen among sister families of teleost fishes for the same region of the mitochondrial genome. These genetically distinct introduced populations in all likelihood represent at least two and possibly three species. Regardless of species status, these genetically distinct lineages may be expected to vary in ecological or life-history traits, representing different potential threats to the ecosystems where they have been introduced. Given the success of swamp eels in invading many habitats around the world, further study of these eels is warranted to elucidate the characteristics of successful invaders and invasions.

Conservation Biology↗
USGS2001

Targeting ecosystem features for conservation: Standing crops in the Florida Everglades

The Everglades in southern Florida, U.S.A., is a major focus of conservation activities. The freshwater wetlands of the Everglades do not have high species richness, and no species of threatened aquatic animals or plants live there. We have, however, identified a distinctive ecological feature of the Everglades that is threatened by canal construction, draining, and nutrient enrichment from agricultural runoff compared to values reported from other freshwater systems, standing stocks of periphyton in relatively undisturbed areas of the Everglades were unusually high, and standing stocks of invertebrates and fish were unusually low. Averaging data gathered from nine sites and five sampling periods spanning I year, we found that periphyton standing crop was 88.2 g/m2 (ash-free dry mass), invertebrate standing stock was 0.64 g/m2 (dry mass), and fish standing stock was 1.2 g/m2 (dry mass of large and small species combined). We found that fish standing stocks were much higher in phosphorus-enriched sites than in nearby reference sites but that invertebrate standing stocks were similar in enriched and reference sites. Our results support the notion that oligotrophy is at least partially responsible for the low standing stocks of fish, but they also suggest that species interactions and a paucity of deep-water refugia are important. Anthropogenic eutrophication in Everglades marshes will lead to the loss of distinctive ecosystem features. A focus on species richness and 'hot spots' of threatened species provides no basis for conservation of ecosystems like the Everglades. If oligotrophic ecosystems often have low species richness, they will be underrepresented in preservation networks based on some common criteria for establishing conservation priorities.

Conservation Biology↗
USGS2001

Separating the effects of intra- and interspecific age-structured interactions in an experimental fish assemblage

We documented patterns of age-structured biotic interactions in four mesocosm experiments with an assemblage of three species of co-occurring fishes from the Florida Everglades, the eastern mosquitofish (Gambusia holbrooki), sailfin molly (Poecilia latipinna), and bluefin killifish (Lucania goodei). These species were chosen based on their high abundance and overlapping diets. Juvenile mosquitofish and sailfin mollies, at a range of densities matching field estimates, were maintained in the presence of adult mosquitofish, sailfin mollies, and bluefin killifish to test for effects of competition and predation on juvenile survival and growth. The mesocosms held 1,200 1 of water and all conditions were set to simulate those in Shark River Slough, Everglades National Park (ENP), USA. We placed floating mats of periphyton and bladderwort in each tank in standard volumes that matched field values to provide cover and to introduce invertebrate prey. Of 15 possible intra- and interspecific age-structured interactions, we found 7 to be present at the densities of these fish found in Shark River Slough marshes. Predation by adult mosquitofish on juvenile fish, including conspecifics, was the strongest effect observed. We also observed growth limitation in mosquitofish and sailfin molly juveniles from intra- and interspecific competition. When maintained at high densities, juvenile mosquitofish changed their diets to include more cladocerans and fewer chironomid larvae relative to low densities. We estimated size-specific gape limitation by adult mosquitofish when consuming juvenile mosquitofish and sailfin mollies. At high field densities, intraspecific competition might prolong the time period when juveniles are vulnerable to predation by adult mosquitofish. These results suggest that path analysis, or other techniques used to document food-web interactions, must include age-specific roles of these fishes.

Oecologia↗
USGS2000

Empirical assessment of fish introductions in a subtropical wetland: An evaluation of contrasting views

We summarized data from eight quantitative fish surveys conducted in southern Florida to evaluate the distribution and relative abundance of introduced fishes across a variety of habitats. These surveys encompassed marsh and canal habitats throughout most of the Everglades region, including the mangrove fringe of Florida Bay. Two studies provided systematically collected density information over a 20-year period, and documented the first local appearance of four introduced fishes based on their repeated absence in prior surveys. Those species displayed a pattern of rapid population growth followed by decline, then persistence at lower densities. Estuarine areas in the southern Everglades, characterized by natural tidal creeks surrounded by mangrove-dominated marshes, and canals held the largest introduced-fish populations. Introduced fishes were also common, at times exceeding 50% of the fish community, in solution holes that serve as dry-season refuges in short-hydroperiod rockland habitats of the eastern Everglades. Wet prairies and alligator ponds distant from canals generally held few individuals of introduced fishes. These patterns suggest that the introduced fishes in southern Florida at present may not be well-adapted to persist in freshwater marshes of the Everglades, possibly because of an interaction of periodic cold-temperature stress and hydrologic fluctuation. Our analyses indicated low densities of these fishes in central or northern Everglades wet-prairie communities, and, in the absence of experimental data, little evidence of biotic effects in this spatially extensive habitat. There is no guarantee that this condition will be maintained, especially under the cumulative effects of future invasions or environmental change.

Biological Invasions↗
USGS1997

Modeling fish dynamics and effects of stress in a hydrologically pulsed ecosystem

Many wetlands undergo seasonal cycles in precipitation and water depth.This environmental seasonality is echoed in patterns of production of fishbiomass, which, in turn, influence the phenology of other components of thefood web, including wading birds. Human activities, such as drainage orother alterations of the hydrology, can exacerbate these natural cycles andresult in detrimental stresses on fish production and the higher trophic levels dependent on this production. In this paper we model theseasonal pattern of fish production in a freshwater marsh, with specialreference to the Everglades/Big Cypress region of southern Florida.The model illustrates the temporal pattern of production through theyear, which can result in very high densities of fish at the end of ahydroperiod (period of flooding), aswell as the importance of ponds and other deep depressions, both as refugia and sinks during dry periods. The model predicts that: (1) there is an effective threshold in the length of the hydroperiod that must beexceeded for high fish-population densities to be produced, (2) large,piscivorous fishes do not appear tohave a major impact on smaller fishes in the marsh habitat, and (3) therecovery of small-fish populations in the marsh following a major droughtmay require up to a year. The last of these results is relevant toassessing anthropogenic impacts on marsh production, as these effectsmay increase the severity and frequency of droughts.

Journal of Aquatic Ecosystem Stress and Recovery↗