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Community assembly is influenced by disturbance intensity, sequential colonization (arrival order) of species, and interactions between species arriving early and species arriving later. We documented both intra- and interspecific patterns of colonization following hydrological disturbance using a 20-year time series of marsh-fish density at 21 study sites located in the Everglades, Florida, USA, as a case study of sequential colonization. The critical swimming speed (UCRIT) of 20 juveniles and 20 adults for six species was estimated using UCRIT tests to evaluate if UCRIT predicted timing of re-colonization. We observed a consistent pattern of species colonization over 500 disturbance events. On average, juveniles of early arriving species were collected prior to adults, while adults consistently appeared prior to juveniles for late-arriving species. Density at first collection was inversely correlated with arrival order; early arriving species tended to have higher density when first collected following marsh re-flooding than later arriving ones. Females consistently arrived before males for all species where sex could be identified. Neither absolute nor size-adjusted UCRIT was correlated with arrival order. Although interspecific colonization was highly repeatable, intraspecific differences among demographic groups were species-specific and possibly tied to reproductive biology and juvenile life history. Juvenile early arrival may indicate rapid colonization of pregnant females (Poeciliidae), diapausing eggs laid before marsh drying, or early development of robust swimming capacity (Cyprinodontidae and Fundulidae); in the Everglades, water currents are absent or too weak to support larval drift as an important mechanism. Stage- and sex-specific UCRIT and reproductive traits such as embryo diapause in oviparous species need more attention to understand successional dynamics following disturbance in aquatic communities. 

Boom-bust population dynamics are long-recognized phenomena during species invasions, but few studies documented impacts of these dynamic changes. The Florida Everglades is the largest wetland in the United States, is undergoing a multi-decade hydro-restoration effort, and has been invaded by several tropical freshwater fishes. We used a 26-year dataset of small native marsh fishes and decapods to assess potential effects of African Jewelfish (Hemichromis letourneuxi) invasion and compared their effects to those of a more recently invading species, Asian Swamp Eels (Monopterus albus/javanensis), and a long-established non-native species, Mayan Cichlids (Mayaheros urophthalmus). Unlike boom-bust dynamics of jewelfish, swamp eel abundance increased and stabilized over the course of this study. After accounting for effects of hydrologic variation, the densities of several native species were more reduced by either jewelfish or swamp eels than by native fish predators, while effects of Mayan Cichlids were similar to those of native fish predators. Impacts of the jewelfish boom in Shark River Slough were smaller (density reductions ≤ 50%) and more temporally limited than those of swamp eels, which produced near-complete loss of four species in Taylor Slough. Following the jewelfish bust, the density of affected species approximated pre-invasion predictions based on hydrology, but their recovery is now threatened by the subsequent invasion of swamp eels in Shark River Slough. Long-term monitoring data provide opportunities to probe for population-level effects at field scales, and indicate that impacts of non-native species can be context-dependent and vary across ecosystems and temporal scales. 

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 affected adversely by hydrological stress and can be applied to a diverse group of taxa. Growth, survivorship, and the transitional age should be evaluated to improve population modelling efforts used to predict the influence of future restoration actions. 

Abstract 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 AlligatorAlligator mississippiensisis 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 and quantitative community analyses, and stoichiometric analyses on plants and animals.Our findings demonstrate that alligators act as ecosystem engineers and enhance food‐web heterogeneity by increasing nutrient availability, manipulating physical structure and altering algal, plant and animal communities. Flocculent detritus, an unconsolidated layer of particulate organic matter and soil, showed strong patterns of P enrichment in ponds. Higher P availability in alligator ponds also resulted in bottom‐up trophic transfer of nutrients as evidenced by higher growth rates (lower N:P) for plants and aquatic consumers. Edge habitats surrounding alligator ponds contained the most diverse communities of invertebrates and plants, but low total abundance of fishes, likely driven by high densities of emergent macrophytes. Pond communities exhibited higher abundance of fish compared to edge habitat and were dominated by compositions of small invertebrates that track high nutrient availability in the water column. Marshes contained high numbers of animals that are closely tied to periphyton mats, which were absent from other habitats.Alligator‐engineered habitats are ecologically important by providing nutrient‐enriched ‘hotspots’ in an oligotrophic system, habitat heterogeneity to marshes, and refuges for other fauna during seasonal disturbances. This work adds to growing evidence that efforts to model community dynamics should routinely consider animal‐mediated bottom‐up processes like ecosystem engineering.