Does a long‐term shift in Wood Stork diet foreshadow adaptability to human‐induced rapid environmental change?

To preserve biodiversity, identifying at‐risk populations and developing conservation plans to mitigate the effects of human‐induced rapid environmental change (HIREC) are essential. Changes in diet, especially for food‐limited species, can aid in detecting populations being impacted by HIREC, and characterizing the quality, abundance, and temporal and spatial consistency of newly consumed food items may provide insight concerning the likelihood of a species persisting in a changing environment. We used Wood Storks (Mycteria americana) nesting in the Florida Everglades as a model system to study the possible effects of HIREC on a food‐limited population. We compared the diets of Wood Storks in 2013 and 2014 with those reported during the 1970s before major anthropogenic activities affected the Everglades system and prey availability. Wood Storks in our study consumed more large‐bodied sunfish species (Lepomis spp.), fewer native marsh fishes, and more non‐native fish species than during the 1970s. Large sunfish and non‐native fish are relatively rare in the drying pools of Everglades marshes where storks traditionally forage, suggesting that Wood Storks may be using novel foraging habitats such as created wetlands (i.e., canals and stormwater ponds). Although created wetlands have long hydroperiods conducive to maintaining large‐bodied fishes and could provide alternative foraging habitat when prey availability is reduced in natural marshes, additional studies are needed to determine the extent to which these wetlands are used by Wood Storks and, importantly, the quality of prey items potentially available to foraging Wood Storks in created wetlands.     

Predator Generalization Decreases the Effect of Introduced Predators in the San Marcos Salamander,Eurycea nana

The introduction of novel predators into an environment can have detrimental consequences on prey species, especially if these species lack the ability to recognize these predators. One such species that may be negatively affected by introduced predators is the federally threatened San Marcos salamander (Eurycea nana). Previous research found that predator‐naïve (captive‐hatched) salamanders showed decreased activity in response to the chemical cues of both a native fish predator (Micropterus salmoides) and an introduced fish predator (Lepomis auritus), but not to a non‐predatory fish (Gambusia geiseri). We tested the hypothesis that E. nana recognized the introduced Lepomis (and other non‐native Lepomis) because they share chemical cues with other native congeneric Lepomis predators in the San Marcos River. We examined the antipredator response of predator‐naïve E. nana to chemical cues from (1) a sympatric native sunfish (Lepomis cyanellus; Perciformes: Centrarchidae); (2) a sympatric introduced sunfish (L. auritus); (3) an allopatric sunfish (Lepomis gibbosus); (4) a sympatric non‐native, non‐centrarchid cichlid (Herichthys cyanoguttatum; Perciformes: Cichlidae); and (5) a blank water control to determine whether individuals make generalizations about novel predators within a genus and across a family. Exposure to chemical cues from all fish predator treatments caused a reduction in salamander activity (antipredator response). Additionally, there were no differences in the antipredator responses to each predatory fish treatment. The similar responses to all sunfish treatments indicate that E. nana shows predator generalization in response to novel predators that are similar to recognized predators. Additionally, the antipredator response to H. cyanoguttatum indicates that predator generalization can occur among perciform families.     

Interactions among stream fishes: predator-induced habitat shifts and larval survival

Summary Adult largemouth bass alter habitat use by, and abundances of, other fishes in small streams. Experimental manipulations of bass in natural stream pools (Brier Creek, Oklahoma) showed that responses of other fishes to adult bass were highly dependent on prey size, and that both direct and indirect effects of adult bass influence the distribution and abundance of other stream fishes. Experiments measuring the distributional responses of members of natural pool assemblages to adult bass revealed differences among adult sunfishes, small fishes (16–80 mm SL), and larval sunfish and minnows. Adult sunfishes (Lepomis spp.) did not detectably alter their depth distribution in response to adult bass, but changes in abundance of adult Lepomis on the whole-pool scale appeared positively related to changes in the number of bass. Small fishes tended to occupy shallower water when adult bass were present; changes in abundance of small fishes were negatively related to the number of adult bass. Larval minnows and larval Lepomis occupied primarily deep, mid-regions of pools, and were found only in pools which contained, or had contained, adult bass. A second set of experiments was motivated by censuses of small prairie-margin streams which revealed co-occurrence of larval fishes (of both minnow and sunfish species) and adult largemouth bass. Experimental manipulation of bass and Lepomis larvae on the whole-pool scale showed that adult bass enhanced short-term survival of Lepomis larvae. This effect appears to be an indirect result of habitat shifts by small fishes in response to bass; additional experiments indicated that these small fishes are potentially important predators of larvae. The interactions suggested in this study are analogous to those hypothesized for bass and sunfish in lakes by Werner and Hall (1988).     

Diet and morphology through ontogeny of the nonindigenous Mayan cichlid ‘<Emphasis Type="Italic">Cichlasoma</Emphasis> (<Emphasis Type="Italic">Nandopsis</Emphasis>)’ <Emphasis Type="Italic">urophthalmus</Emphasis> (Günther 1862) in southern Florida

We evaluated diet and morphology through ontogeny for a freshwater population of the Mayan cichlid Cichlasoma (Nandopsis) urophthalmus (Günther 1862) in Floridas Big Cypress National Preserve. This species is a generalist predator throughout ontogeny. Fish remained the primary prey item throughout ontogeny, but there was a shift from detritus and ostracods among juveniles to algae, gastropods (snails), decapods, Hymenoptera, and adult Diptera among adults. All morphological variables grew isometrically except total molariform tooth area and pharyngeal jaw mass, which exhibited positive allometry. Despite a moderately robust adult pharyngeal jaw apparatus, this species does not specialize on hard prey at this south Florida site. Compared to its native range in Mexico, fish in Florida have undergone a pronounced niche shift with the diet being dominated by fish and snails, probably due to greater availability. The invasive success of C. urophthalmus does not appear to be related to ontogenetic morphological shifts or dietary specialization. Rather, its successful and rapid colonization of southern Florida might in part be related to its generalized and opportunistic feeding habits and morphology.     

Prey use of wetland benthivorous sunfishes: ontogenetic, interspecific and seasonal variation

The intensity of competitive interactions between fishes is partly determined by prey use and ontogenetic niche shifts. In a wetland where distinct habitat shifts are missing we compared prey use of three generalist benthivorous sunfishes to look for evidence of ontogenetic, interspecific, and “seasonal” variation in prey composition. Diet analysis revealed evidence of diet ontogeny in warmouth (Lepomis gulosus, 30–152 mm standard length, SL), but not in bluespotted sunfish (Enneacanthus gloriosus, 30–47 mm SL) or dollar sunfish (Lepomis marginatus, 30–60 mm SL). Bluespotted and dollar sunfishes consumed small dipteran and amphipod prey and had similar diets in both seasons suggesting a potential for strong interspecific competition. In the dry season, warmouth shifted from using smaller insect prey to larger decapod and fish prey with increasing size. This shift to prey types that were little used by the other species reduced dietary niche overlap with the other sunfishes. After drought and re-flooding (in the wet season), decapods and small fish were less abundant in the wetland and the warmouth ontogenetic shift was less distinct. When matched for gape width, prey composition differed between warmouth and both dollar and bluespotted sunfishes in the wet season, suggesting differences in sunfish foraging modes, but prey use differences were less clear in the dry season when prey were abundant. Both warmouth ontogenetic diet shifts and seasonal variation in prey use (probably mediated by prey abundance) had strong influences on diet overlap and therefore the potential for intra- and interspecific competition between sunfishes in this wetland ecosystem.     

Seasonal variation in pH and alkalinity and recruitment of sunfish populations

• 1 In a study of five ponds sensitive to acid precipitation, we document seasonal acidification profiles and assess the impact of short-term acid pulses on the reproductive success of resident sunfish (Lepomis spp.).
• 2 Three years of water sampling at 2–3 week intervals showed substantial seasonal variation in pH and alkalinity consistent with a carbonate buffering system. Though all ponds shared a common seasonal pattern in pH, ponds with relatively low pH and alkalinity showed the greatest variation in these parameters. Spring minima may dispose some of the ponds towards episodes of extreme acidity during heavy spring rains.
• 3 Otolith analysis of young-of-the-year sunfish revealed recruitment failures for eggs laid early in spring in ponds with relatively low alkalinity and pH, and, in the most extreme case, missing day classes at subsequent irregular intervals even though average pH and alkalinity were well above those demonstrated to affect centrarchid fishes.
• 4 Age-class distributions of sunfishes revealed gaps in adult age distributions which could be traced through 3 years of the study, but there was no clear-cut relationship between pond acidification and the age structure of adult fish.
• 5 Seasonal profiles of acidity may enable researchers to predict the time during which a pond or lake may be highly sensitive to acid inputs. Comparative otolith analysis of young-of-the-year fishes and short-term continuous monitoring of water chemistry may provide an early warning of biological effects of acidification in sensitive bodies of water.

     

Potential for successful population establishment of the nonindigenous sacred ibis in the Florida Everglades

The nonindigenous sacred ibis (Threskiornis aethiopicus) was first discovered breeding in the Florida Everglades in 2005 in the Arthur R. Marshall Loxahatchee National Wildlife Refuge. Prior to this, sacred ibises were seen periodically throughout South Florida since the mid 1990s, with occasional confirmed breeding occurrences in Miami-Dade and Palm Beach counties. We used a logistic regression model developed by Allen (Biol Invasions 8:491–500, 2006) to predict the probability of successful establishment of sacred ibis in the Florida Everglades ecosystem. Empirical data collected from several sacred ibis nests and chicks were used to validate those findings. The probability of successful establishment was estimated to be 73%. The physiological condition of nestlings suggested that this species was able to fledge chicks in good condition, thus adding to the potential to increase their breeding population. Exponential population growth rates and expanding distribution of the nonindigenous sacred ibis in France demonstrate this species’ potential for becoming invasive in Florida. We suggest that the most prudent and effective management strategy is eradication of the few pioneering individuals that are nesting in the Everglades as well as the urban source population.     

Effects of a non-native cichlid fish (African jewelfish, Hemichromis letourneuxi Sauvage 1880) on a simulated Everglades aquatic community

In an 8-month mesocosm experiment, we examined how a simulated Everglades aquatic community of small native fishes, snails, and shrimp changed with the addition of either a native predator (dollar sunfish Lepomis marginatus) or a non-native predator (African jewelfish Hemichromis letourneuxi) compared to a no-predator control. Two snail species (Planorbella duryi, Physella cubensis) and the shrimp (Palaemonetes paludosus) displayed the strongest predator-treatment effects, with significantly lower biomasses in tanks with Hemichromis. One small native fish (Heterandria formosa) was significantly less abundant in Hemichromis tanks, but there were no significant treatment effects for Gambusia holbrooki, Jordanella floridae, or Pomacea paludosa (applesnail). Overall, there were few treatment differences between native predator and no-predator control tanks. The results suggest that the potential of Hemichromis to affect basal food-web species that link primary producers with higher-level consumers in the aquatic food web, with unknown consequences for Florida waters.     

Estimating the spawning activity of fish species using nuclear and mitochondrial environmental DNA concentrations and their ratios

1. During spawning activity, fish release large amounts of sperm and eggs into the water, which has been assumed to cause an increase in environmental DNA (eDNA) levels and nuclear DNA/mitochondrial DNA ratios. To test whether these assumptions are valid and whether nuclear and mitochondrial eDNA analysis can be used to monitor the spawning activity of freshwater fish, we conducted field eDNA surveys and traditional surveys using common carp (Cyprinus carpio), largemouth bass (Micropterus salmoides) and bluegill sunfish (Lepomis macrochirus) as model species.
2. Fish spawning periods were estimated based on age, as estimated using the body lengths of juveniles collected in the Miharu reservoir in Fukushima, Japan. The results showed that the main spawning periods of largemouth bass and bluegill sunfish were from April to July and from July to August, respectively.
3. Field eDNA surveys were conducted in the Hebisawagawa front reservoir, which is connected to the Miharu reservoir. From March to August 2019 and 2020, weekly eDNA sampling was conducted at three sites, and daily sampling was conducted at six sites from 23 June to 3 July 2020. The eDNA concentrations of the nuclear internal transcribed spacer 1 (ITS1) and mitochondrial cytochrome B (CytB), as well as the ITS1/CytB ratio, were measured for each of the three fish in each water sample. Water temperature had a statistically significant effect on eDNA concentration, probably reflecting the relationship between water temperature and spawning.
4. We created generalised additive mixed models to estimate spawning activity periods based on weekly eDNA data. The estimated periods of spawning activity for common carp, largemouth bass and bluegill sunfish were March to May, May to July, and May to August, respectively. The estimated spawning periods coincided with known fish ecology or the results of traditional methods. This method also has been applied to daily eDNA samples, showing the feasibility of high-resolution estimation of spawning activity.
5. For common carp and bluegill sunfish, we were able to estimate the spawning period using this method. Although the method is affected by biomass and the diffusion and degradation of eDNA, it has the potential to accurately estimating spawning activities. These then can be estimated without conducting laborious traditional surveys, facilitating the monitoring of reproduction by rare, invasive or important fishery species. Further research on the diffusion distance and degradation time of the eDNA concentration peak caused by fish spawning activity may improve the accuracy of monitoring.

     

Post‐Hurricane Regeneration of Pioneer Plant Species in South Florida Subtropical Hardwood Hammocks1

After Hurricane Andrew crossed southern Florida (U.S.A.) on 24 August 1992, native and exotic pioneer species in subtropical hardwood forests (hammocks) regenerated from seed banks. Regeneration occurred in hammocks of metropolitan Dade County and the Long Pine Key region of Everglades National Park. The density of the native pioneer Trema micrantha was significantly higher in hammocks of Long Pine Key than in those of metropolitan Dade County. In contrast, the basal area of the exotic pioneer Carica papaya was greater in Dade County hammocks than Long Pine Key hammocks. Although T. micrantha tended to be restricted to areas of soil disturbance (tip‐up pits) formed by trees uprooted during Hurricane Andrew, especially in Long Pine Key, C. papaya was located throughout hammocks. These results suggest differences in the regeneration niches in which the native T. micrantha required more specific disruptions (i.e., both canopy and soil) than C. papaya (only removal of canopy) for establishment. A broad regeneration niche could in part account for the capability of an exotic species with a dormant seed bank to invade native subtropical forests following natural large‐scale disturbances.     

Can a highly invasive species re-invade its native community? The paradox of the red shiner

Red shiners (Cyprinella lutrensis) are among the most widespread, ecologically general, and environmentally tolerant fish species in North America, and are highly invasive where they have been introduced outside their native range. However, long-term data on fish assemblages showed that red shiners gradually (1980s to 2006) disappeared from creeks that are direct tributaries of Lake Texoma (Oklahoma, USA) where they are native and historically had been numerically dominant. Following a major flood in 2007, red shiners were detected anew in some of these creeks, but repeatedly disappeared and re-appeared through November 2009. Given their invasive abilities where they are not native, their failure to become re-established prompted us to examine factors that affect their apparent inability to re-invade their native habitat. We established assemblages of five common fish taxa native to Brier Creek in 12 large, outdoor mesocosm stream units. Subsequently, we introduced red shiners at two densities of 10 or 30 per unit, six replicates each, to examine potential effects of propagule pressure on establishment success. Approximately six months later, we ended the experiment and recovered all fish. Red shiners failed to become established in the experimental units, regardless of initial stocking density. They also exhibited much lower survival than other species in the native community, which not only survived well but exhibited some recruitment. Red shiner survival was significantly negatively related to the number of sunfish (Lepomis spp.) that grew to adult size in experimental units, suggesting that predation can inhibit early stages of invasion by red shiners.     

Changes in Diet and Food Consumption of Largemouth Bass Following Large-scale Hydrilla Reduction in Lake Seminole, Georgia

Largemouth bass Micropterus salmoides Lacepède growth (in length) increased an average of 14% and bioenergetics modeling predicted a 38% increase in total annual food consumption following a large-scale reduction of hydrilla Hydrilla verticillata L.f. Royle in Spring Creek, a 2,343-ha embayment of Lake Seminole, Georgia. Coverage of submersed aquatic vegetation (SAV) declined from 76% to 22% in 1 year due to a drip-delivery fluridone treatment. In contrast, largemouth bass growth only increased an average of 4% and bioenegetics modeling predicted a 13% increase in total food consumption over the same time period in the Chattahoochee River embyament, where SAV coverage naturally declined from 26% to 15%. Diets were collected from a total of 4,409 largemouth bass over a 2.5-year period in the two embayments; the primary diet item (by weight) for largemouth bass in both embayments was sunfish (mostly Lepomis spp.). Diets before and after SAV reduction were generally similar for fish greater than stock-size (≥203 mm) in the Spring Creek arm; however, fewer invertebrates were consumed after SAV reduction. Low diet similarity was observed in smaller fish, caused by a decline in consumption of grass shrimp and sunfishes and an increase in use of damselflies, shiners Notropis spp., and topminnows Fundulus spp. after SAV reduction. Diets were similar between the same time periods for all sizes of fish in the Chattahoochee River arm. These results agreed with many laboratory results describing the effects of aquatic plant density on largemouth bass food consumption and growth, and demonstrated that increased predation efficiency resulting from decreased plant abundance was likely a stronger factor determining growth rates than any potential diet shift that may occur as a result in vegetation decline.     

Variable growth and longevity of yellow bullhead (Ameiurus natalis) in the Everglades of south Florida,USA

Yellow bullhead (Ictaluridae: Ameiurus natalis) is the most abundant ictalurid catfish in the Everglades of southern Florida, USA, and, as both prey and predator, is one of many essential components in the ecological‐simulation models used in assessing restoration success in the Everglades. Little is known of its biology and life history in this southernmost portion of its native range; the present study provides the first estimates of age and growth from the Everglades. In total, 144 yellow bullheads of 97–312 mm total length (TL) were collected from canals and marshes of the Everglades between April 2000 and January 2001, and from October 2003 to February 2005. Fish were aged using cross‐sections of pectoral spines and ranged from 1–12 years, with the maximum age almost twice that of any yellow bullhead previously reported. Yellow bullheads from south Florida grew relatively rapidly during their first 3 years, but after age 5 growth slowed and fish approached an asymptote of ～214 mm TL. Compared to other populations in the United States, yellow bullhead in the Everglades grew relatively slowly, were smaller at age overall, but survived to older ages.     

Cold weather and the potential range of invasive Burmese pythons

The Burmese python (Python molurus bivittatus) is established in Everglades National Park and neighboring areas in south Florida. Beyond its substantial ecological impacts to native fauna in south Florida, concerns have been raised as to its potential to occupy other parts of the USA, even as far north as Washington, DC. During a recent period of cold weather, seven of nine captive Burmese pythons held in outdoor pens at our facility in north-central Florida died, or would have died absent our intervention. This cold-induced mortality occurred despite the presence of refugia with heat sources. Our findings cast doubt on the ability of free-ranging Burmese pythons to establish and persist beyond the subtropical environment of south Florida.     

Freshwater ascomycetes: <Emphasis Type="Italic">Aliquandostipite minuta</Emphasis> (Jahnulales,Dothideomycetes), a new species from Florida

An undescribed ascomycete similar to species in the Aliquandostipitaceae (Jahnulales, Dothideomycetes) was collected from submerged wood in a freshwater swamp in Big Cypress National Preserve, Florida. The characteristic features of the new species are as follows: (i) ascomata are small, sessile, light brown, globose to subglobose, papillate, and anchored to the substrate by wide, brown, septate and subtending hyphae; peridial wall is composed of 1 to 2 layers of large, angular cells with large lumens; (ii) asci are ovoid to broadly clavate, and fissitunicate; (iii) ascospores are one-septate, fusiform, multiguttulate, pale brown, surrounded by a fusiform gelatinous sheath, and equipped with numerous filamentous appendages around the midseptum. The new fungus is most similar to Aliquandostipite crystallinus, from which it differs in overall smaller size and morphology. This new fungus is described and illustrated herein as A. minuta.     

Indirect effects of fish on foraging behaviour and leaf processing by the isopod Lirceus fontinalis

1. We examined whether the isopod, Lirceus fontinalis, an important facultative shredder in low-order streams in the eastern United States, responded to chemical cues of the skin mucus of five fish species varying in relatedness and feeding habits, and if fish-induced alterations in the foraging activity of isopods indirectly affected leaf processing. 2. In the laboratory, isopods generally responded to the presence of fish mucus by reducing their activity. Isopods were most responsive in water containing the skin mucus of predatory sunfish (Lepomis) and least responsive in water treated with mucus from algivorous stonerollers (Campostoma anomalum). 3. Rates of leaf disc breakdown by isopods in the laboratory were significantly reduced when isopods were exposed to chemical cues of confined green sunfish (L. cyanellus). 4. The rate of leaf processing in a fishless reach of a headwater stream was four to five times greater by isopods 7—10mmTL (total length) than those ≤ 5mm TL. Rates of leaf processing by isopods in low-order streams may be affected directly by the size structure of the isopod population and indirectly by the presence of fish.     

Differential sensitivity of CYP1A to 3,3′,4′,4-tetrachlorobiphenyl and benzo(a)pyrene in two Lepomis species

Although Lepomis species are abundant in a wide variety of habitats throughout North America and could serve as potentially valuable biomonitoring tools, few studies have examined the induction of pollutant biomarkers in this genus. We hypothesized that the induction of cytochrome P-450 1A (CYP1A), a sensitive and widely used indicator of response to aquatic contaminants, would serve as an effective biomarker of organic pollutant exposure in Lepomis species. We examined the response of CYP1A and two of the major pollutant-responsive phase II enzymes, glutathione S-transferase (GST), and uridine diphosphate glucuronyltransferase (UDPGT), in Lepomis exposed to organic pollutants under laboratory and field conditions. Two Lepomis species (longear sunfish, Lepomis megalottis and bluegill, Lepomis macrochirus) were exposed in the laboratory via intraperitoneal injection to corn oil (vehicle), benzo(a)pyrene (BaP) (10 and 50 mg/kg), a polynuclear aromatic hydrocarbon (PAH) or 3,4,3′,4′-tetrachlorobiphenyl (PCB 77) (0.1 and 1.0 mg/kg), a dioxin-like planar halogenated aromatic hydrocarbon (HAH), and sacrificed 2 (BaP) or 7 (corn oil, PCB77) days later. Lepomis hepatic CYP1A exhibited differential sensitivity to these two classes of environmental contaminants. CYP1A activity was weakly induced in bluegill exposed to 1.0 mg/kg PCB 77 (3 fold induction over controls) but strongly induced in both bluegill and longear sunfish exposed to 50 mg/kg BaP (37 and 15 fold induction over controls, respectively). In contrast, hepatic GST activity in both species remained unchanged following the treatment with either compound and hepatic UDPGT activity, which was assessed only in BaP-treated longear sunfish, was unaffected by that chemical, indicating these phase II enzymes may not be sensitive pollutant biomarkers in this genus. Further, longear sunfish collected from a PCB contaminated site displayed relatively low levels of CYP1A activity despite PCB body burdens associated with strong induction of CYP1A activity in other fish species. The strong induction of CYP1A by BaP with much weaker CYP1A response to PCB indicates that CYP1A in Lepomis sp. could be an excellent biomarker for PAH pollution, but may not be a reliable indicator of site contamination by halogenated hydrocarbons. We conclude that Lepomis species provide a useful model for examining the regulation and potential consequences of differential pollutant sensitivity, but that CYP1A in these species should be used with caution as an indicator of halogenated contaminants.     

Seeking the sun in deep,dark places: mesopelagic sightings of ocean sunfishes (Molidae)

Evidence is presented from publicly available remotely operated vehicle (ROV) footage that suggests deep‐water ranging in ocean sunfishes (family Molidae) is more common than typically thought, including a new maximum depth recorded for the southern sunfish Mola ramsayi.     

The spatial pattern and dispersion of Lygodium microphyllum in the Everglades wetland ecosystem

Since 1958, L. microphyllum (Old World Climbing Fern), which originated from the Old World Tropics, has become a nuisance exotic and has rapidly spread and is being established system-wide in extremely remote and undisturbed areas such as the Florida Everglades. Of particular concern is that L. microphyllum is disrupting, at an alarming rate, the flora and fauna of the native ecosystem at the same time that a major 8.4 billion dollar Everglades restoration program is trying to enhance these same attributes. This research utilized IKONOS satellite data to map L. microphyllum within the 58,000-ha Loxahatchee National Wildlife Refuge wetland in south Florida. Results show that approximately 11.6% of the tree/shrub vegetation within the impoundment has been infected by L. microphyllum. These data were then utilized to explore the spatial spread patterns of L. microphyllum within the Refuge. Results suggest that L. microphyllum is more likely to establish on the southeast side of a tree/shrub island and then spread to the northwest, which corresponds to the prevailing wind direction in south Florida. Spatial pattern analysis of L. microphyllum spread indicated that it is correlated with the density and spatial distribution of tree/shrub island vegetation. It appears that the dispersion of L. microphyllum is density dependent, which can be expressed as a logistic function and has a catastrophic threshold of 160 m of mean distance between tree/shrub islands in the Everglades. It is predicted that 38% (or 1910 ha) of tree/shrub islands in the Refuge will be invaded by L. microphyllum by 2012. Tree islands in the Everglades wetland could be considered similar to oceanic islands throughout the world that are notoriously vulnerable to biological invasions.     

Consumptive effects of fish reduce wetland crayfish recruitment and drive species turnover

Predators and dry-disturbances have pronounced effects on invertebrate communities and can deterministically affect compositional turnover between discrete aquatic habitats. We examined the effect of sunfish (Lepomis spp.) predators on two native crayfish, Procambarus alleni and P. fallax, that regionally coexist in an expansive connected wetland in order to test the hypotheses that sunfish predation limits crayfish recruitment (both species) and that it disproportionately affects P. alleni, the species inhabiting temporary wetlands. In replicate vegetated wetlands (18.6 m²), we quantified summertime crayfish recruitment and species composition across an experimental gradient of sunfish density. Separately, we quantified effects of sunfish on crayfish growth, conducted a complimentary predation assay in mesocosms, and compared behavior of the two crayfish. Sunfish reduced P. alleni summertime recruitment by >99% over the full sunfish gradient, and most of the effect was caused by low densities of sunfish (0.22–0.43 m⁻²). P. alleni dominated wetlands with few or no sunfish, but the composition shifted towards P. fallax dominance in wetlands with abundant sunfish. P. fallax survived better than P. alleni over 40 h in smaller mesocosms stocked with warmouth. Sunfish reduced P. fallax recruitment 62% in a second wetland experiment, but growth rates of caged crayfish (both species) were unaffected by sunfish presence, suggesting predatory effects were primarily consumptive. Consistent with life histories of relatively fish-sensitive invertebrates, P. alleni engaged in more risky behaviors in the laboratory. Our results indicate that sunfish predators limit recruitment of both species, but disproportionately remove the more active and competitively dominant P. alleni. Spatially and temporally variable dry-disturbances negatively co-varying with sunfish populations allow for regional coexistence of these two crayfish and may release populations of either species from control by predatory fishes.