and Species-dependent effects on Crayfish (Procambarus spp.)

Transcription

1 Wetland Drying has Substrate- and Species-dependent effects on Crayfish (Procambarus spp.) Populations. Nathan J. Dorn Florida Atlantic University Davie, FL SFWMD #

2 1. Relationship between drying and disturbance. Dorn, NJ & JC Volin JNABS 28: Net effect of hydrologic variation (drying) on P. fallax populations. Drying event: marsh water levels < 0 cm

3 Disturbance: a discrete event that removes biomass. The correlation between a hydrologic event and a disturbance is situational (Poff 1992)

4 What combinations of crayfish and substrate are most and least resistant to dry-disturbances?

5 Two species of crayfish Procambarus alleni (Everglades Crayfish) P. fallax (Slough Crayfish) Short Hydroperiod gradient Long

6 Three primary substrates in south Florida wetlands. Reddy, Grunwald and Newman

7 Avera ge water depth (c m) Crayfish Density (# #/m 2 ) Taylor Slough, ENP 12 P. fallax 10 P. alleni Apr-04 Apr-05 Apr-06 Apr-07 Apr Apr-04 Apr-05 Apr-06 Apr-07 Apr-08 Loxahatchee NWR 12 P. fallax 10 P. alleni Apr-04 Apr-05 Apr-06 Apr-07 Apr Apr-04 Apr-05 Apr-06 Apr-07 Apr-08

8 Experimental design 2 x 3 Factorial 2 species (P. alleni, P. fallax) 3 substrates (Peat, Marl, Sand) 18 gal. perforated tubs filled with 27 cm of substrate. Crayfish were added in groups of 4 adults to each tub mm mean carapace lengths. Tubs were placed inside large cement tanks at UF-IFAS Davie Campus. N = 15 of each combination

9 Response variables: 1. Burrowing success (ability to get belowground) 2. Survival over the two month dry-down

10 Last 40 days Start of experiment

11 Dep pth (cm) Time course of Experimental Drought Burrowing observations End of Experiment Day of Experiment

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13 P. alleni P. fallax 4 Mean number burrowed after 4 weeks Sand Marl Peat Substrate

14 Species P = Substrate P < Species x Substrate P < P. alleni Mean number surviving 2 months 3 2 P. fallax b c b b 1 a a 0 Sand Marl Peat Substrate

15 Review Experimental Results 1) P. alleni in marl and both species in peat had relatively high resistance to drying. 2) P. fallax is sensitive to drying in marl and losses probably depend on the length of the dry period. 45% loss in 3 weeks (Dorn and Trexler 2007) 45% loss in 3 weeks (Dorn and Trexler 2007) 69% loss in 9 weeks (this study)

16 What is the net effect of drying on crayfish (P. fallax) ) density and population growth?

17 Three mechanistic ways drying/low water could affect crayfish densities. Water levels/ Drying Burrowing Shortened Predator Stress hydroperiod reduction Crayfish density

18 Densities of P. fallax from Water Conservation Areas. ( ) Conservation Areas: Loxahatchee NWR & WCA 3A (12 sites) Sites: 25 ha each Seasons: July-Aug and Jan. Throw Traps: 5/site Hydrology: EDEN

19 density fallax d t #/m 2 ) age P. (sqrt Avera LOX sites WCA 3A sites Average Depth over the past 360 days (cm)

20 nsity lax den /m 2 ) e P. fall sqrt #/ verage ( Av 5 4 WCA 3A sites LOX sites Average Depth over the past 360 days (cm)

21 Water levels/ Drying + ibis Burrowing Stress Predator Reduction - + Crayfish density Early Wet Season Early Dry Season?

22 Is wet season population p growth enhanced following drying events? Population Growth ~ LN (Jan dens/july dens) WCA 3A for water years

23 MODEL HYPOTHESES/TERMS 1. Is POPN GR density-dependent? dependent? (July DENSITY) 2. Does wetland drying enhance POPN GR? (DRY conditions in last dry season) 3. Is POPN GR reflecting local distribution/conc.? (DEPTH during January sampling)

24 Model Selection Results for POPN GR in WCA 3A Model AICc w i evidence ratio Density, Dry Density, Dry, Depth Density, Depth Density Dry Dry, Depth Depth Best model: R 2 = 0.57

25 pulatio on Grow wth Ra ate Po Population Growth in WCA 3A Replacement rate Average July Density (#/m 2 )

26 Population Growth in WCA 3A Pop pulation Grow wth Rat te Dry Wet Average July Density (#/m 2 )

27 Recap of the talk: 1) P. alleni are stronger burrowers and generally suffer less under dry conditions, but it depends on the substrate. P. fallax burrows and survives well in peat substrate! 2) P. fallax (Slough crayfish) densities in WCA 3A are generally higher when the sloughs have been shallower over the past year. 3) Wet season P. fallax POPN GR appears to be both density-dependent and enhanced by dry events in WCA3A 3A.

28 Acknowledgements J. Newman, SFWMD RECOVER (# ) M. Cook, SFWMD Everglades Division (# ) J. Volin and his research staff. Field and lab help: R. Boyle, R. Crespo, C. Kellogg, J. Konyha, J. Nelson, E. Peters, C. van der Heiden, S. van der Heiden. UF-IFAS (J. Korvak) - for use of the tank facility. E. Cline and E. Gaiser - for help locating soils.

29 Bulk density of soils: Peat (0.098 g/cm 3 ) Marl (0.204 g/cm 3 ) Reddy, Grunwald and Newman Sand (1.24 g/cm 3 )

30 Average belowground depths (cm) of survivors recovered from each substrate. Species Sand Marl Peat P. fallax None P. alleni Model Averaged Parameter Estimates ± 95% CI Density: ± Flooded Conditions: ± 1.07

31 Fate of crayfish in this experiment (%). Substrate Species Mortality on Mortality Surviving Relative Mortality Total surface (failure upon re- after 2 Resistance to underground Mortality to burrow) emergence months Drought Sand P. alleni Low-Moderate P. fallax Low Marl P. alleni High P. fallax Low-Moderate Peat Palleni P High P. fallax High Resistance may depend on vegetation *S See Discussion i re: drought htlength and dbody condition.

32 Length-Weight Relationships (body condition) Log 10 Dry weight (m mg) P. fallax Intercept: p = Slope: p = Initial 2.8 Marl survivors 2.6 Peat survivors % loss Log 10 Carapace length

33 Log 10 Dry weight (m mg) P. alleni Intercept: p = Slope: p = Initial Marl survivors Peat survivors 9% loss? Log 10 Carapace length

34 Burrows Surface deaths

35 Idea #2. Ecosystem Function. Crayfish may respond numerically to drought years and enhance bird production in years following droughts. Suggestion from this study: Based on the throw trap data from WCA 3A and the high h resistance to drought in peat soils (in the experiment), occasional drought/low water events may enhance P. fallax population growth in regions that still have peat soils.