Seasonal Fish Dispersal in Ephemeral Wetlands of the Florida Everglades

HYDROLOGIC RESTORATION

Seasonal Fish Dispersal in Ephemeral Wetlandsof the Florida Everglades

Charles W. Goss & William F. Loftus & Joel C. Trexler

Received: 13 August 2012 /Accepted: 8 January 2013# Society of Wetland Scientists 2013

Abstract We hypothesized that fishes in short-hydroperiodwetlands display pulses in activity tied to seasonal floodingand drying, with relatively low activity during interveningperiods. To evaluate this hypothesis, sampling devices thatfunnel fish into traps (drift fences) were used to investigatefish movement across the Everglades, U.S.A. Samples werecollected at six sites in the Rocky Glades, a seasonally floodedkarstic habitat located on the southeastern edge of theEverglades. Four species that display distinct recovery pat-terns following drought in long-hydroperiod wetlands werestudied: eastern mosquitofish (Gambusia holbrooki) and flag-fish (Jordanella floridae) (rapid recovery); and bluefin killi-fish (Lucania goodei) and least killifish (Heterandriaformosa) (slow recovery). Consistent with our hypothesizedconceptual model, fishes increased movement soon afterflooding (immigration period) and just before drying (emigra-tion period), but decreased activity in the intervening foragingperiod. We also found that eastern mosquitofish and flagfisharrived earlier and showed stronger responses to hydrologicalvariation than either least killifish or bluefin killifish. Weconcluded that these fishes actively colonize and escapeephemeral wetlands in response to flooding and drying, anddisplay species-specific differences related to flooding and

drying that reflect differences in dispersal ability. These resultshave important implications for Everglades fish metacom-munity dynamics.

Keywords Directed dispersal . Metacommunity .

Change-point analysis . Fish . Aquatic refuge

Changes in habitat use, activity level, and movement strategiesof animals may be adaptive responses to environmental fluc-tuation (Armsworth and Roughgarden 2005; Nams 2006). Forexample, as habitat patch quality deteriorates, optimal foragingtheory suggests individuals should increase exploratory behav-ior and the frequency of long-distance displacements to gainbetter information about other habitat patches. These behav-ioral changes can decrease the odds of time wasted in low-quality sites and reduce the risk of being stranded in a danger-ous site (Fretwell and Lucas 1970; Fretwell 1972). In aquaticecosystems, fluctuations in habitat quality favoring dispersalinclude changes in oxygen availability, predation risk andwater depth and temperature (Cucherousset et al. 2007;Correa et al. 2008; Rayner et al. 2008; Mosepele et al. 2009;Schofield et al. 2009), as well as food availability and sites forreproduction (Lowe-McConnell 1987). In wetlands, flood-plains, arid-zone rivers, and littoral zones, seasonal fluctuationsin water depth may be so severe as to strand aquatic animals(Chapman et al. 1991; Perry and Bond 2009). Environmentalfluctuation also may provide temporary access to previouslyunavailable high-quality habitats that provide food resourcesand reproductive sites free from predators for species able tocolonize transient environments. In such variable environ-ments, behaviors sensitive to the changing risk of strandingby habitat loss and that enable exploitation of newly availablehabitat should be favored (Resetarits 2001; Segev et al. 2011).

Though ecologists have always been aware of the limi-tations of assuming closed populations and communities,

C. W. Goss (*) : J. C. TrexlerDepartment of Biological Sciences, Florida InternationalUniversity, North Miami, FL 33181, USAe-mail: [email protected]

W. F. LoftusAquatic Research & Communication, LLC, Vero Beach, FL32967, USA

Present Address:C. W. GossSchool of Environment and Natural Resources, Ohio AgriculturalResearch and Development Center, Ohio State University,Wooster, OH 44691, USA

WetlandsDOI 10.1007/s13157-013-0375-3

increased attention during the past two decades has been paidto spatial ecology, and metapopulation and metacommunitydynamics. Much ofmetapopulation andmetacommunity ecol-ogy has been spatially implicit, but recently efforts havefocused on using behavioral rules of movement to integratespatial dynamics into theory (Jacobson and Peres-Neto 2010).Fisher (1937) and Skellam (1951) proposed ecological analy-sis of movement by establishing a null model of diffusionbased on three behaviors: movement speed, time dispersing ina direction, and turning angle. The speed, time moving in aparticular direction, and turning angle determine individualdisplacement and, collectively, population spread across alandscape. Despite their historical significance, simple diffu-sion models tend to predict spreading that is too slow torespond to environmental fluctuation (DeAngelis et al. 2010and citations therein). Thus, bias in turning angle and speedthat affect directedness of spread may be common. At thepopulation level, changes in the speed and directionality ofmovement in response to cues of habitat change determine theability of a species to persist in a spatially complex andtemporally fluctuating environment (Armsworth andRoughgarden 2005; Abrams et al. 2007; Jacobson andPeres-Neto 2010). In aquatic systems, change in water chem-istry, presence of desiccated conspecifics, and elevated intraand interspecific density may act as cues that indicate chang-ing habitat quality (Magoulick and Kobza 2003; Davey andKelly 2007; Sadeh et al. 2011). Spatial complexity and tem-poral fluctuation are ubiquitous features of wetlands, and fishmovement dynamics in these systems likely play an importantrole in metapopulation and metacommunity persistence.

The Florida Everglades is a large landscape of hydrological-ly dynamic, shallow wetlands, where hydrologic connectivityamong permanent and ephemeral habitats facilitates fish

persistence throughout this system. Aquatic habitat size of theEverglades fluctuates seasonally, with the spatial extent ofdrying varying annually in roughly decadal cycles of droughtseverity (Childers et al. 2006; Gaiser et al. 2012). Annualfluctuation in the spatial area of flooding leads to local variationin the time between drying events. Local drying forces fishes tomove to areas that remain inundated; those individuals that failto respond appropriately die from desiccation or predation.Regional drying can limit fish communities and drive transi-tions in community composition as the time since a regionaldrying event increases (Ruetz et al. 2005; Trexler et al. 2005).Three life-history strategies related to recovery followingdrought have been identified within the Everglades fish assem-blage: rapid recovery and sustained high density (eastern mos-quitofish - Gambusia holbrooki); rapid recovery followed bydecline in density as time since re-flooding increases (flagfish -Jordanella floridae); and slow recovery over a number of yearsto an asymptotic density (bluefin killifish - Lucania goodei andleast killifish - Heterandria formosa) (DeAngelis et al. 2005;Trexler et al. 2005). The relative contributions of immigrationand local reproduction in supporting those recovery patterns arenot well understood, but reproduction alone cannot explain thefirst two patterns, as all age classes appear in samples soon afterre-flooding (unpublished data). Furthermore, the magnitude offish emigration from wetlands prior to drying is uncertain, as isits effect on population and community responses to drought inthe Everglades landscape.

In this study, we sought to characterize patterns of fishactivity in response to hydrologic variation in the FloridaEverglades (Fig. 1). To investigate fish immigration and emi-gration in response to annual flooding and drying, we focusedon short-hydroperiod wetlands that dry completely every year.Eastern mosquitofish, flagfish, least killifish and bluefin

Fig. 1 Location of the RockyGlades region (stippled area) inEverglades National Park,Florida, U.S.A., with study sitesindicated by numbers. TheRocky Glades outside of ENP isnot stippled because it has beenconverted to agriculture

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killifish were monitored because of their documented differ-ences in recovery following hydrologic disturbance (DeAngeliset al. 2005; Trexler et al. 2005). Our primary objectives were todetermine whether fish-activity patterns change in predictableways in response to flooding and drying and whether there areinterspecific differences in response to flooding and drying.Wehypothesized that there are three distinct periods of fish activitythat correspond to hydrologic conditions: 1) immigration peri-od, a response to flooding, 2) emigration period, a response todrying, and 3) an intervening foraging period (Fig. 2). Theduration of these periods is expected to be shortest when fishactivity is elevated (immigration and emigration periods) andlongest when fish activity is depressed (foraging period). Wealso hypothesized that eastern mosquitofish and flagfish arrivesooner, have stronger responses to both flooding and drying,and are generally more dominant numerically than either leastkillifish or bluefin killifish.

Methods

Study Area and Sampling Method

From 2000 to 2004 fishes were sampled in the RocklandRidge, aka Rocky Glades, a karstic short-hydroperiod wetlandin the eastern portion of the Everglades National Park (ENP)(Fig. 1). Here the water table drops below the ground surfacefor extended periods of time and supports a substrate ofmainly limestone and marl instead of peat (a long-hydroperiod Everglades soil). Vegetation in the RockyGlades is characterized by semi-aquatic gramminoids andupland shrubs, with bayheads and tree islands on topographichighs and aquatic plants in solution holes (Craighead 1971).

Fishes were sampled by constructing six drift-fences in theRocky Glades (Loftus et al. 2001). To determine populationdynamics and successional patterns in the wetlands, we sam-pled from 2000 to 2004 at four sites (sites 1-4) located along

the ENPmain road, and from 2001 to 2004 at two sites (sites 5and 6) located north of the road (Fig. 1). Park policies andlogistics limited work to sites that could be reached on foot.The X-shaped structures had 12-m wings of black plasticagricultural ground cloth to direct animals into metal minnowtraps (3-mm mesh) at the center (see Obaza et al. 2011). Tocapture fishes moving across the landscape at sites 1 through 4the traps faced three directions (N, E, W), while sites 5 and 6had traps facing all four cardinal directions (N, S, E, W). Theminnow traps were set overnight and fishes were removedafter approximately 24 h to yield fish catch-per-unit-effort(CPUE). Following wetland flooding, samples were takendaily for the first 2 weeks, twice weekly for the next 2 weeks,and finally weekly for the rest of the wet season until allwetlands dried. We saw no evidence that repeated visits tothe sites affected the local habitat because the hard karstlimestone substrate and the sparse emergent/submerged veg-etation resisted trampling. Therefore, site visits likely resultedin little to no consistent effects on our data.

Our data, as well as other studies (e.g., Obaza et al.2011), indicate that CPUE obtained from drift-fence min-now traps are indicative of fish activity rates. In cases whereboth drift-fence CPUE and throw-trap samples of fish den-sity are available, little or no correlation has been found(Hoch et al., unpublished manuscript). Following Obaza etal. (2011), we use the term “encounter rate” to refer to drift-fence CPUE because the traps are stationary and fish mustencounter and enter the trap to be captured, implying fishare moving; stationary fish will not be caught.

Depth measurements obtained at permanent staff gauges ateach drift fence were adjusted to reflect local variation inelevation. Measurements were taken frequently to capturehydrological variation [on average approx. every 11 days; lessfrequently when the wetland was dry (depth=0) and morefrequently when the wetland was wet (depth>0)]. To estimatehydrologic parameters, we interpolated data among days byretaining the previous measurement until the next recordedmeasurement. The hydrologic parameters we estimated fromthe data were: 1) Hydroperiod - the number of days thewetlandwas flooded (depth>0) within a given water year; 2) FloodingEvent - the intervening time between dry periods when thewetland is inundated with water; 3) Days Since Flooding(DSF) – at the time of sampling, the number of continuousdays that a marsh has been flooded (this value resets each timethe water depth reaches zero). Because the study sites are onlyinundated for a portion of each year and rainfall that floodsthem is variable annually, we defined a “water year” to corre-spond to a period that begins near the onset of the rainy season(April) and ends at the termination of the dry season thefollowing year (March). In instances when there was an earlypulse of rain indicating the onset of the wet season, we pushedback the date to include March; we also pushed up the date ofthe beginning of the water year if a site dried later.

Immigration Emigration

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Fig. 2 A conceptual model of how fish-movement rate is related to thenumber of days since wetland flooding. We hypothesized that there arethree distinct periods of movement in response to hydrologic variation:an immigration period with increased movement in response to flood-ing; an emigration period with increased movement that is a responseto drying; and a foraging period between those two periods whenmovement is reduced

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Data Analysis

The response variable in our analysis was the mean numberof fishes caught in all minnow traps at each drift fence (3–4traps/fence). When one or more of the traps was compro-mised (e.g., fell out of drift fence), or if the wetland was dry,the sample was treated as missing. In some instances, trapswere set in anticipation of flooding to capture fish immedi-ately after they moved into a wetland. This sometimesresulted in heterogeneity among traps (i.e., some traps weresubmerged longer than others) and less than 24 h of total“soak time”. Because those samples were important to cap-ture pulses of movement, we included them in the analysesand treated them as equal to periods when all traps arecompletely submerged for the entire 24-h period.

To capture variation in fish movement throughout theyear, we used a change-point analysis (reviewed inAndersen et al. 2009). In the present study the purpose ofusing a change-point analysis was to determine where thereare statistically detectable shifts in fish encounter rate as aflooding event progresses. Fish encounter-rate data wereanalyzed using the changepoint package (Killick and Eckly2012) in R (R Core Team 2012), which can be used toidentify breaks in a time series based on changes in the meanand variance. We used the Schwartz Information Criterion(SIC) and the binary segmentation search algorithm to detectchanges in the mean and variance of fish encounter ratewithin a given flooding event (assuming a normal distribu-tion). In this analysis, the number of change points is deter-mined by the fit statistics (e.g., SIC) and by specifying amaximum number of change points to be fit. The maximumnumber of change points was set to three (to yield at mostfour temporal segments), which enabled us to capture vari-ation in the data related to our conceptual model of threediscrete periods (Fig. 2), and to accommodate “extra” peri-ods of movement such as if there was low fish movementprior to an immigration pulse (for an example of an extraperiod, see least killifish graph in Fig. 5). We were interestedin flooding events where enough samples were collected tobe able to detect at least one transition between periods (e.g.,immigration to foraging period). Because a minimum of fourobservations are needed to obtain two separate estimates forthe mean and variance, we did not analyze flooding eventswhere less than four samples were collected. Although thechange-point analysis assumes equally spaced data points,we found that it adequately detected trends in our unequallyspaced observations. As an estimate of model fit, we calcu-lated a mean r2 value across sites and years using estimatesfrom change-point models with the equation: r2=1 – (resid-ual sums of squares/total sums of squares).

Within a flooding event, we defined the immigrationperiod as the first pulse (i.e., elevated mean estimate relativeto adjacent temporal segments) in movement after flooding

of a wetland (1 per flooding event); the emigration corre-sponded to the last pulse in movement prior to wetlanddrying (1 per flooding event). If the first pulse in movementcontinued until the end of the time series, we defined it asthe emigration period. All other periods were defined as theforaging period, and as a result there were some floodingevents with more than one foraging-period estimate (seeFigs. 2 and 5 for examples of different periods).

After we determined the different temporal segmentsfrom the change-point analysis, we estimated 95 % confi-dence intervals for the means of three different responsevariables during each period for each species to characterizeresponses to hydrologic variation: 1) timing of each period(the time point at which one segment changed to another, orthe end of a flooding event); 2) the duration of each period;and 3) the fish encounter-rate estimates for each period. Thetiming and duration of each period was estimated by calcu-lating proportion DSF variables that measure when a partic-ular period ended relative to the duration of the entireflooding event (period timing=maximum DSF within aperiod/maximum DSF for entire flooding event) and thetotal duration of a period relative to the duration of the entireflooding event (period duration=total # of days within aperiod/maximum DSF for entire flooding event). Thesevariables provide a comparable measure of response amongflooding events of varying duration. Because of variation inmovement patterns among flooding events (e.g., an eventwith an immigration, but no emigration period), we detectedunequal numbers of movement periods over the course ofthe study: 35, 28, 24, 26 immigration periods were detectedfor eastern mosquitofish, flagfish, least killifish and bluefinkillifish, respectively; 19, 19, 15, 18 emigration periods; and58, 59, 43, and 51 foraging periods. Data from each periodwere aggregated by estimating the mean within water yearsand then among water years to yield one mean estimate foreach of the three response variables (timing, duration andencounter rate) at each site, and these mean estimates wereused to generate period specific 95% confidence intervalestimates for each response variable (six total observationsfor each confidence interval estimate). Only five observa-tions were used for the least killifish emigration pulse esti-mate because this species did not exhibit an emigrationpulse at Site 2. Although aggregating the data across yearswithin sites homogenizes some of the variation in the data,we were interested in extracting general patterns that weredetectable regardless of site-level idiosyncrasies. In someinstances there was more than one estimate for the foragingperiod within a flooding event; in those instances we esti-mated the mean encounter rate within a flooding event andthen aggregated the data as we did the other periods. Forthese analyses we focused on the effects, given that therewas at least one change point observed within a givenflooding event. Therefore, if there were no change points

Wetlands

for a given event (i.e., a constant value was fit for the entiretime series), it was not used to estimate confidence intervals.We interpreted mean estimates as different (i.e., significant)if the 95 % confidence intervals did not overlap.

Results

Site Hydrology

Though our study sites encompassed a range of hydroper-iods, all sites completely dried during each year of the study(Fig. 3). Sites 1 and 2 had the shortest mean hydroperiodestimates (96.8 and 97.5 days, respectively), followed by

sites 3 and 6 (178 and 168.7 days, respectively), with sites 4and 5 having the longest mean hydroperiod estimates (273and 238.3 days, respectively). The mean and maximumnumber of days since flooding were positively related tohydroperiod, with means ranging from approximately 6to 104 days and 76 to 332 days for the maximum(Table 1). The total number of flooding events rangedfrom 6 events at Site 4 to 19 events at Site 2, with allother estimates in between (Table 1). Although therewere exceptions, sites generally flooded (depth>0) be-tween May and August and dried (depth=0) betweenNovember and March, with longer hydroperiod sitesflooding earlier and drying out later than the shorterhydroperiod sites (Fig. 3).

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Fig. 3 Time-series graph ofwater depths during the studyplotted separately for each site.Sites are grouped byhydroperiod

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Fish Summary Statistics

Fish encounter-rate estimates showed marked differencesamong species. Over this four-year study we collected95,236 fish at the six study sites. Eastern mosquitofish(76.1 % of total catch) had a mean encounter rate of 80.2fish/day, flagfish (19.1 %) a mean encounter rate of 20.1fish/day, least killifish (3.4 %) a mean encounter rate of 3.6fish/day, and bluefin killifish (1.4 %) had a mean encounterrate of 1.4 fish/day. This overall ranking of species encoun-ter rates was consistent across sites (Table 2). Eastern mos-quitofish had the highest maximum number of individualscaptured during a single sampling event at all sites, andflagfish had the second highest single-day capture of indi-viduals at four of the six sites (Table 2). There were alsodifferences among species in the order in which they arrivedin the wetland. The confidence interval estimates of the rankorder of fish arrival indicated that flagfish and eastern mos-quitofish were generally the first to arrive, while least killi-fish and bluefin killifish took longer to colonize (Fig. 4).

Change-Point Analyses

Our change-point analyses indicated considerable variabilityin model fits and movement dynamics among species.Overall, we fit 164 models (41 flooding events for eachspecies over all years and sites) with a mean of approxi-mately 21 observations per model and a range of 4 to 64 permodel. The mean r2 values across sites and years werehigher for eastern mosquitofish and flagfish than for leastkillifish and bluefin killifish (Table 3). However, regardlessof species, the models were able to explain a substantialamount of variation in the data, with maximum r2 valuesranging from 0.65 to 0.94. All species exhibited pulses inactivity more frequently when immigrating into a wetland(range of 26 to 36 segments) than when leaving a wetland(range of 13 to 18 segments), with eastern mosquitofish andflagfish having greater numbers of immigration and emigra-tion segments than either least killifish or bluefin killifish.

For all species, the number of flooding events during whichfishes responded to both flooding and drying of wetlandswas similar to the number of emigration segments, indicat-ing that in periods when fish emigrated in response to

Table 1 Summary statistics for hydrologic data at each site across allyears. DSF corresponds to the number of consecutive days of wetlandflooding (depth>0). Events correspond to the number of floodingevents over the course of the study

Site Mean Hydroperiod Mean DSF Max DSF Events

1 96.8 7.2 77 11

2 97.5 6.4 76 19

3 178.0 33.0 192 15

4 273.0 104.2 332 6

5 238.3 65.2 252 11

6 168.7 20.2 126 16

Table 2 Encounter-rate (# of fish collected/24 h) summary statisticsfor all species at each site aggregated across years

Site Species Mean Max

1 Eastern Mosquitofish 79.0 1998

1 Flagfish 7.3 85

1 Least Killifish 5.3 138

1 Bluefin Killifish 1.1 13


2 Flagfish 36.2 595




3 Flagfish 12.4 364




4 Flagfish 19.5 234




5 Flagfish 24.4 494




6 Flagfish 22.4 245



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Fig. 4 Estimates of the rank order of arrival means and 95 % confi-dence intervals for each species. Rankings were determined by assign-ing a rank based on the first instance a species was collected duringeach flooding event (e.g., 1=first species to arrive, 2=second speciesto arrive, etc.). Species were ranked equally if they arrived on the sameday, and if they did not appear in samples during a flooding event theywere given a rank of one higher than the last species to arrive (e.g., ifthe last species to arrive was ranked 3 then a species that did not appearwould be given a rank of 4). Non-overlapping confidence intervalsindicate significant differences

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drying, they also had immigrated in response to wetlandflooding earlier in the event (Table 3). All species exhibitedpulses in greater than 60 % of the models with easternmosquitofish having the highest percentage, followed byflagfish and bluefin killifish, and least killifish had thelowest percentage. The total number of change points esti-mated for both eastern mosquitofish and flagfish was higherthan for the other two species (Table 3).

Of the flooding events that exhibited detectable variation inencounter rate through time (i.e., at least one change point),the change-point analyses indicated that all species exhibiteddistinct periods of movement (Fig. 5). The confidence intervalestimates of the timing for each period (immigration, emigra-tion and foraging as measured in proportion DSF) indicatedthat the study species moved during similar time periods. Forall species the immigration period occurred earlier than theemigration and foraging periods, and two of the four species

had later emigration periods than foraging periods (Fig. 6).Within each period there were no detectable differences in thetiming of movement among species. Our estimates of periodduration showed that for two of the four species, the immi-gration period was shorter than the foraging period (Fig. 7).We found no detectable species-specific differences in dura-tion among any of the other periods. However, when weaggregated the species duration estimates within periods therewas a slight trend of lower mean duration for both the immi-gration and emigration periods relative to the foraging period(see dotted lines on Fig. 7). As with the timing of the periods,duration estimates were indistinguishable among species.

In contrast to similarities in the timing and duration offish activity, the change-point analyses revealed markeddifferences in the encounter-rate estimates among species.Our estimates of mean encounter rate in each period showedthat eastern mosquitofish had higher encounter rates in the

Table 3 Results from change-point analysis across all sites and years.Change points correspond to the total number transitions betweenimmigration, emigration and foraging periods; % models with pulsesis the percentage of models where the change-point analysis detected atleast one period with a pulse in activity (i.e., at least one change pointwithin a flooding event); immigration is the total number of segments

occurring in the first (immigration) period; emigration refers to thetotal number of segments in the last (emigration) period; both corre-sponds to the total number of flooding events during which bothimmigration and emigration periods occurred; mean and max r2 corre-spond to the model fits aggregated across years and sites, and themaximum r2, respectively

Species Change points % Models with pulses Immigration Emigration Both Mean r2 Max r2

Eastern Mosquitofish 76 88 35 19 18 0.33 0.94

Flagfish 75 76 28 19 16 0.36 0.88

Least Killifish 56 63 24 15 13 0.20 0.65

Bluefin Killifish 65 73 26 18 14 0.24 0.81

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Observed Immigration Foraging EmigrationFig. 5 Plots of mean estimatesfrom change-point analyses(colored lines) overlain onobserved data. The plotsillustrate trends in encounterrates throughout a floodingevent, with the highestencounter rates duringimmigration and emigrationperiods, and lowest duringforaging periods. The graphsshow data from Site 4, wateryears 2001, 2002, and 2003(eastern mosquitofish, bluefinkillifish, and flagfish), and Site3, water year 2001 (leastkillifish)

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immigration and emigration periods than in the foragingperiod (Fig. 8). Flagfish mean encounter rates in both theforaging and emigration periods were lower than the immi-gration period. The encounter rate in the immigration periodfor least killifish was higher than the foraging period(difference in means was<4 fish/day), but there were nodifferences among the foraging and emigration periodestimates. There were no detectable differences in meanencounter rates among any of the periods for bluefinkillifish. Eastern mosquitofish and flagfish had higherencounter rate estimates than least killifish and bluefinkillifish in both the immigration period and the foragingperiod. Eastern mosquitofish had the highest emigration-period estimate of any species, while flagfish had ahigher emigration estimate than least killifish, but notbluefin killifish (Fig. 8).

Discussion

Consistent with our conceptual model of fish movement, ourresults indicate that fish alter their activity rates in responseto hydrological variation. Pulses in movement soon afterflooding and just prior to drying suggest that fish are active-ly moving into and out of short-hydroperiod wetlands inresponse to seasonal hydrological fluctuations. Further,there was evidence of species-specific differences in activitylevels that correspond to patterns of recovery followingdisturbance in long-hydroperiod wetlands (DeAngelis et al.2005; Trexler et al. 2005). Our results are consistent withtheoretical work on the importance of behavioral differencesin movement for structuring communities (Armsworth andRoughgarden 2005; Abrams et al. 2007), and suggest thatthe interaction between dispersal and the environment is akey process driving metacommunity dynamics in theEverglades landscape.

Results from this study suggest that eastern mosquitofishand flagfish move in large groups into short-hydroperiodwetlands, and are generally more abundant in ephemeralaquatic habitats than either least killifish or bluefin killfish.These data add to a growing body of evidence that recoveryfrom hydrological disturbance is a primary driver of fish-community structure in the Everglades. Several studies haveillustrated the importance of hydrological disturbance driv-ing successional dynamics of fish communities in long-hydroperiod environments (Ruetz et al. 2005; Trexler et al.2005; McElroy et al. 2011). The current study expands ourinference to include environments that are disturbed annu-ally and border the long-hydroperiod sites where past workhas focused.

Our analysis of change-point results corroborated thehypothesis that fish can exhibit three distinct movementperiods in ephemeral wetlands. Fish exhibited pulses inactivity soon after flooding or prior to drying in the majorityof flooding events we analyzed: eastern mosquitofishexhibited pulsed activity in almost 90 % of the models,

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Fig. 6 Estimates of the period timing means and 95 % confidenceintervals for each species. Period timing corresponds to the ending of aparticular period and is measured as a ratio of the number days sinceflooding (DSF) observed at the change point for each period divided bythe maximum DSF observed in a flooding event. Non-overlappingconfidence intervals indicate significant differences

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Fig. 7 Estimates of the period duration means and 95 % confidenceintervals for each species. Period duration is the length of a periodmeasured as a ratio of the total duration of a particular period (mea-sured in days) divided by the maximum number of days since flooding(DSF) observed in a flooding event. Non-overlapping confidenceintervals indicate significant differences. Dotted lines correspond tothe approximate mean estimate of all species for each period

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Fig. 8 Estimates of encounter rate means and 95 % confidence inter-vals during each period for each species. Non-overlapping confidenceintervals indicate significant differences

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flagfish and bluefin killifish in about three quarters of themodels, and least killifish in greater than 60 % of themodels. When at least one pulse in activity was detected,we found that immigration period occurred earlier than theforaging and emigration periods for all species, and theemigration period occurred later than the foraging periodfor two of four species. Similarly, we found general trends inthe mean duration of each period with foraging being thelongest and emigration and immigration the shortest; how-ever, these results were more equivocal with only two spe-cies exhibiting shorter immigration period than foragingperiod, and no detectable differences observed for any spe-cies between the emigration and the other two periods. Highvariance in the estimates of emigration duration possiblyreflects the inter-site variability in wetland drying.

In contrast to the relatively consistent timing and duration ofperiods among species, encounter-rate estimates revealedmarked differences among species in response to hydrologicalvariation. Change-point analyses described eastern mosquito-fish and flagfish data better and indicated more responsivenessto hydrological variation than bluefin killfish and least killifish.During the immigration period, encounter-rate estimates foreastern mosquitofish and flagfish were higher than the encoun-ter rates of least killifish and bluefin killifish in all otherperiods. This suggests that eastern mosquitofish and flagfishare able to quickly disperse into newly available habitats inrelatively large numbers, while relatively few individuals ofleast killifish and bluefin killifish are able to respond to flood-ing. These results may indicate heterogeneity in behavioraladaptations enabling detection and response to environmentalcues (Lytle and Poff 2004), and may explain differences inrecovery observed in long hydroperiod environments(DeAngelis et al. 2005; Trexler et al. 2005). Immigration andemigration encounter-rate estimates for eastern mosquitofishwere not different, and were higher than all other estimateswith the exception of the flagfish immigration estimate. Strongresponses by eastern mosquitofish to both flooding and dryingis not surprising because this species is well documented as agood disperser (Brown 1985, 1987; Capone and Kushlan1991; Congdon 1994; Rehage and Sih 2004; Ruetz et al.2005), and has become invasive in many areas (Courtenayand Meffe 1989; Pyke 2008). Our results suggest that itsresponsiveness to both flooding and drying may contribute toits widespread success. Obaza et al. (2011) indicated that driftfences may be slightly less efficient at capturing eastern mos-quitofish than the other study species. Thus, the resultsreported here are inconsistent with the species differencesexpected by this bias, and the high encounter rate estimatesfor eastern mosquitofish are probably conservative.

Our results provide empirical support for the importance ofdispersal for connecting local fish communities in theEverglades. Species-specific differences in dispersal is a keycomponent of metacommunity models where patterns in

community structure are shaped by both local (e.g., competi-tion) and regional scale processes (e.g., dispersal). In particu-lar, patch dynamics models predict species that wouldnormally be inferior competitors in a given patch can persistregionally via superior colonization ability (e.g., acompetition-colonization trade-off) (Leibold et al. 2004).Empirical studies of Everglades fish communities where somespecies exhibit quick recovery to disturbance followed by adecline in density (e.g., flagfish) while others recover slowlybut become dominant as time increases following a distur-bance (e.g., bluefin and least killifish) indicate that trade-offsbetween dispersal and competitive ability may be important inexplaining species coexistence in this system (DeAngelis et al.2005; Trexler et al. 2005). Eastern mosquitofish recoversquickly and persists at high densities through time, suggestingthat other mechanisms may explain its dynamics. In the pres-ent study, movement patterns were consistent with previousestimates of interspecific differences in recovery, and rein-forced the inference that fish recovery to disturbance is drivenby dispersal. Although there are likely other mechanismsdetermining fish coexistence in this system, strong interspe-cific differences in dispersal ability suggest that trade-offsoperating at regional spatial scales may play a role in mediat-ing species coexistence in this system.

Overall, the results of our study are consistent with aconceptual model in which small fishes in the Evergladesdisplay three periods of movement throughout the year:immigration, foraging, and emigration. Although three peri-ods of movement did not occur in every flooding event, inthe majority of flooding events that we analyzed, the timingof the periods is relatively consistent across species andthere is evidence that the immigration period occurs over arelatively short period of time. There are also interspecificdifferences in the magnitude of response to flooding anddrying that likely reflect differences in dispersal ability thatmay drive larger scale patterns in response to disturbance.Although the drift-fence sampling methodology also allowsestimation of the direction fish are moving, in this study ourfocus was on differences in overall activity levels in re-sponse to hydrological variation. Future research shouldexplore the potential directedness of movement in the im-migration and emigration phases of this seasonal cyclewhich would enhance our understanding of how fishespersist in this fluctuating environment. The results of thisstudy have important implications for predicting the conse-quences of hydrological management of peripheral wetlandsin the Everglades, and for developing models for manage-ment assessment and evaluation (Trexler and Goss 2009;Jopp et al. 2010). This study also reinforces the importanceof regional scale processes influencing Everglades fishcommunities and suggests that metacommunity theorymay provide insight into the mechanisms shaping fishcommunity structure in this system.

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Acknowledgments This publication was produced for a special issuedevoted to investigating the ecological response of over 20 years ofhydrologic restoration and active management in the Taylor Sloughdrainage of ENP. Support was provided by ENP, the Southeast Environ-mental Research Center, the Florida Coastal Everglades Long-TermEcological Research program (National Science Foundation cooperativeagreement #DBI-0620409), the Everglades Foundation, and the SouthFlorida Water Management District. We greatly appreciate the help oftechnicians who built the arrays, tested sampling gear, and processedsamples: V. Foster, R. Kobza, D. Padilla, X. Pagan, D. Riggs, H. Waddle,A. Martin, B. Shamblin, and R. Urguelles. B. Zepp saw us through theENP permit process and Dr. S. Howington supported our work as NPSCESI coordinator and project administrator. D. Elswick and C. Fadeley ofUSGS helped with budget and personnel needs. WFL was supported inpart by funds from the Critical Ecosystem Studies Initiative (CESI)Interagency Cooperative Agreement between USGS and NPS # 5280-7-9023. CWG and JCT were supported in part by Critical EcosystemStudies Initiative (CESI) Cooperative Agreement H50000 06 0104, tasksJ5284 06 0023 and J5284 06 0020 between FIU and the National ParkService while working on this project.

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Seasonal Fish Dispersal in Ephemeral Wetlands of the Florida Everglades