Joel Trexler

The potential for animals to modify spatial patterns of nutrient limitation for autotrophs and habitat availability for other members of their communities is increasingly recognized. However, net trophic effects of consumers acting as ecosystem engineers remain poorly known. The American Alligator Alligator mississippiensis is an abundant predator capable of dramatic modifications of physical habitat through the creation and maintenance of pond‐like basins, but its role in influencing community structure and nutrient dynamics is less appreciated. We investigated if alligators engineer differences in nutrient availability and changes to community structure by their creation of ‘alligator ponds’ compared to the surrounding phosphorus (P)‐limited oligotrophic marsh. We used a halo sampling design of three distinct habitats extending outward from 10 active alligator ponds across a hydrological gradient in the Everglades, USA. We performed nutrient analysis on basal food‐web resources an...

Two species of herons (Aves: Ardeidae), the great egret and the snowy egret, fed preferentially on relatively large individual sailfin mollies (Pisces: Poeciliidae). The level of selectivity by great egrets decreased when plant cover was added to the experimental conditions. We documented the preference of snowy egrets for large mollies in all combinations of two prey sex ratios and two prey size distributions with 50% plant cover. Snowy egrets chose females preferentially to males when females were rare, but not when they were commmon. This preference may be caused by the larger overall size of females when gravid in comparison to males of the same length and/or by the behavior of females when they are in a minority relative to males. Selective predation by wading birds is likely to contribute to patterns of size variation among some populations of sailfin mollies but not to the patterns of female-skewed sex ratios in adults.

In large‐scale conservation decisions, scenario planning identifies key uncertainties of ecosystem function linked to ecological drivers affected by management, incorporates ecological feedbacks, and scales up to answer questions robust to alternative futures. Wetland restoration planning requires an understanding of how proposed changes in surface hydrology, water storage, and landscape connectivity affect aquatic animal composition, productivity, and food‐web function. In the Florida Everglades, reintroduction of historical hydrologic patterns is expected to increase productivity of all trophic levels. Highly mobile indicator species such as wading birds integrate secondary productivity from aquatic prey (small fishes and crayfish) over the landscape. To evaluate how fish, crayfish, and wading birds may respond to alternative hydrologic restoration plans, we compared predicted small fish density, crayfish density and biomass, and wading bird occurrence for existing conditions to f...

The Everglades is an internationally recognized iconic, wetland threatened by water extraction, channelization, and anthropogenic nutrient enrichment. It is a large oligotrophic, karstic wetland with seasonal climate influenced by its location at the southern tip of the Florida peninsula between the subtropical Western Atlantic and the Gulf of Mexico, notable for the large breeding aggregations of pelicaniform and ciconiiform wading birds it supported historically. Though greatly reduced, large populations of these birds still nest there, and a major restoration program is under way in an effort to reclaim some of its lost ecological functions. Aquatic invertebrates play a critical role in linking the physical features of this ecosystem to apex predators through their place in the food web. This chapter reviews the ecological linkages of aquatic invertebrates of the Everglades to the remarkable accumulation of periphyton in complex mats and their role as prey for higher trophic levels. It also explores the role of aquatic invertebrates in some of the challenges confronting managers and scientists involved in the restoration process. Despite those fundamental roles, aquatic invertebrate systematics, distribution, and ecology remain poorly understood and documented. More work on biodiversity and ecological processes is needed to fully understand their importance in the Everglades.

Recruitment has been linked to decreases in the ratio of age-specific mortality (M′) to mass-specific growth (G′), and year-class strength may be predicted by the age when M′/G′ = 1. Hydrological stress adversely affects these parameters for species inhabiting floodplains; however, the relationship between M′ and G′ in hydrologically variable environments is poorly understood. We evaluated age-specific mortality for six species from a 20-year time series and growth curves from otolith length-at-age data. We assessed the effect of hydrology on the transitional age (age M′/G′ = 1) at 21 sites representing a hydrological gradient. Disturbance intensity influenced age-specific mortality but had no effect on mass-specific growth. The transitional age was inversely correlated with annual density, but weakly associated with population biomass. Hydrological disturbance shifted the transitional age to older ages, reducing recruitment overall. We demonstrated that the M′/G′ transition was aff...

Page 1. OIKOS 69: 250-258. Copenhagen 1994 Size-selective predation of sa n moes by two species of ero Joel C. Trexler, Robert C. Tempe and Joseph Travis Trexler, JC, Tempe, RC and Travis, J. 1994. Size-selective predation of sailfin mollies by two species of heron. ...

With the recent funding of the Comprehensive Everglades Restoration Plan (CERP), the largest ecosystem restoration program ever attempted, there is a pressing need to be able to detect changes in natural habitats as a result of restoration actions. Human activities, ...

This multi-year program embodying facility construction, maintenance, and experiments is nearing the end of its funding cycle. The experimental mesocosm array was constructed in Everglades National Park as a cooperative effort of FIU, USGS, and NPS to address questions about predator-prey, competitive, and indirect interactions difficult to study in the field. Two experiments that examined mosquitofish predation and competition with other cohabiting small fishes in the Everglades marshes have been completed. Results showed that growth of juvenile mosquitofish could be limited by the presence of other juveniles at densities within the range found in the Everglades. This suggests that food limitation is a potential factor for juvenile fishes in Everglades marshes, as had been suggested by earlier field studies. The relative role of food versus predator limitation is central to any model of fish population dynamics, such as the ATLSS model. We have completed the study of spotted sunfish nest predation by small fishes, especially mosquitofish, which demonstrated a feedback loop in the Everglades food web. Mosquitofish prey upon eggs and larvae of spotted sunfish, which in turn eat mosquitofish as they grow. Water level was inversely related to the degree of nest predation and probably helps explain why sunfish populations grow during high water years. The mesocosm is now being used to address the role of nutrient inputs into the Everglades in causing shifts in marsh food webs.

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

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 specie...

Page 1. Hurricane Andrew's Impact on Freshwater Resources Water quality, so important to defining the Everglades' ecological composition, appears little affected unique Charles T. Roman, Nicholas G. Aumen, Joel C. Trexler ...

This paper synthesizes research conducted during the first 5–6 years of the Florida Coastal Everglades Long-Term Ecological Research Program (FCE LTER). My objectives are to review our research to date, and to present a new central theme and conceptual approach for future research. Our research has focused on understanding how dissolved organic matter (DOM) from upstream oligotrophic marshes interacted with a marine source of the limiting nutrient, phosphorus (P), to control productivity in the oligohaline estuarine ecotone. We have been working along freshwater to marine transects in two drainage basins located in Everglades National Park (ENP). The Shark River Slough transect (SRS) has a direct connection to the Gulf of Mexico, providing this estuarine ecotone with a source of marine P. The oligohaline ecotone along our southern Everglades transect (TS/Ph), however, is separated from this marine P source by the Florida Bay estuary. We originally hypothesized an ecosystem productiv...

... The method of Slatkin (1981, 1985a) em-ploys the relationship between migration Page 6. GENETIC VARIATION IN THE SAILFIN MOLLY 1011 rate and the frequency of rare neutral alleles. ... A quantitative estimate can be obtained from the equation (Barton and Slatkin, 1986) ...

Herbivory is thought to be an inefficient diet, but it independently evolved from carnivorous ancestors in many metazoan groups, suggesting that plant-eating is adaptive in some circumstances. In this study, we tested two hypotheses to explain the adaptive evolution of herbivory: (i) the Heterotroph Facilitation hypothesis (herbivory is adaptive because herbivores supplement their diets with heterotrophic microbes); and (ii) the Lipid Allocation hypothesis (herbivory is adaptive because algae, which have high lipid concentrations, are nutritionally similar to carnivory). We tested these hypotheses using enclosure cages placed in the Everglades and stocked with Sailfin Mollies (), a native herbivore. Using shading and phosphorus addition (P), we manipulated the heterotrophic microbe and lipid composition of colonizing epiphyton and examined the effects of varying food quality on Sailfin Molly life history. Epiphyton grown in "shade only" conditions had a 55% increase in bac...

ABSTRACT Background/Question/Methods Movement by animals can have major influence on metapopulations and metacommunities. Florida’s Everglades ecosystem is an important wetland with annual variation in hydrology. Small fish rapidly move in and out of flooding or drying portions of the wetland more rapidly than predicted by reaction-diffusion. Modeling suggests that the rates at which wetlands are colonized can be explained by fish following a dynamic ideal free distribution, wherein fish climb fitness gradients (driven by food availability drought escape). We developed a sampling method capable of measuring fish activity, orientation of movement and displacement over the landscape. We investigated whether local-level directional movement can be scaled up to show regional-level migrations, whether behavioral states are distributed in a way that enhance migration to favorable environments and whether behaviors vary between hydrologic seasons or among regions with different hydrological regimes. Results/Conclusions We tested those hypotheses for the most abundant small fish (the eastern mosquitofish, Gambusia holbrooki) in two largely separated regions of the Everglades that have different hydrological properties. We confirmed our ability to demonstrate site-level directional movement by observing similar direction and magnitude of movement with multiple, simultaneous traps within sites. In short-hydroperiod sites, during periods of water recession mosquitofish appear to move in large pulses; these pulses were not observed in the long hydroperiod sites. Both movement speed and directional dispersion was strongly related to water-recession rate in short hydroperiod sites (directional movement was oriented in tighter clusters when water levels were falling), but not obviously in the direction of known refuges. In long-hydroperiod sites, directional dispersion was also non-random, but the speed of movement was much lower. These data show that geographic displacement (total movement of populations over the landscape) is greatest in short-hydroperiod wetlands as water-level falls. Intense pulses of movement were not observed during the period of rising water; this may be a result of differing fitness gradients driving migration or our inability to sample the earliest migrations because of limited ability to sample in the shallowest water levels. Overall, the fish appear to switch behavioral states between non-migratory activity during periods of stable water and a state of rapid directional movement during periods of change. We demonstrate that these small fish in a large, semi-continuous landscape move non-randomly and that their dispersal is consistent with models predicting movement in a manner that climbs fitness gradients as fish move away from drying regions to avoid stranding.

... Copeia 1983. 375–382. Greven, H., and M. Grossherr. 1992.. Adelphophagy and oophagy in Ameca splendens Miller & Fitzsimons, 1971 (Goodeidae, Teleostei). Zietschrift f;auur Fischkunde 1:193–197. Hester, FJ 1964.. ... Zoologica 32:1–15. Thibault, RE, and RJ Schultz. 1978.. ...

A major challenge of movement ecology is to understand how an organism's motivation and environment affect its movement behavior. The Everglades encompass a water-permanence gradient with flooding periods from nearly permanent in central sloughs to very short-...