LIFE HISTORY VARIATION IN INVADING APPLESNAILS (“POMACEA CANALICULATA”) MAY POSE ECOLOGICAL...
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LIFE HISTORY VARIATION IN INVADING APPLESNAILS (“ LIFE HISTORY VARIATION IN INVADING APPLESNAILS (“ POMACEA POMACEA CANALICULATA” CANALICULATA” ) MAY POSE ECOLOGICAL THREAT TO WETLANDS ) MAY POSE ECOLOGICAL THREAT TO WETLANDS INTRODUCTION INTRODUCTION ABSTRACT ABSTRACT METHODS METHODS RESULTS RESULTS DISCUSSION DISCUSSION FUTURE PLANS FUTURE PLANS In our experiments, exotic, invasive, In our experiments, exotic, invasive, channeled applesnails demonstrated their: channeled applesnails demonstrated their: 1) ability to respond to predators; 2) 1) ability to respond to predators; 2) capability of surviving moderate capability of surviving moderate environmental stress; 3) sensitivity to environmental stress; 3) sensitivity to intraspecific competition; 4) and their intraspecific competition; 4) and their susceptibility to predation by native susceptibility to predation by native predators. predators. With their reproductive capacities, With their reproductive capacities, generalist feeding, and genetic diversity, generalist feeding, and genetic diversity, CAS represent a serious ecological threat CAS represent a serious ecological threat to estuarine and freshwater systems. to estuarine and freshwater systems. P. “canaliculata” P. “canaliculata” did not survive salinity did not survive salinity levels >14ppt. Thus, storm surges typical levels >14ppt. Thus, storm surges typical of tropical storms or hurricanes could of tropical storms or hurricanes could damage applesnail populations in estuarine damage applesnail populations in estuarine systems. However, none of our results systems. However, none of our results indicated that the snails would not thrive indicated that the snails would not thrive in freshwater systems as well. in freshwater systems as well. Environmental and biotic stresses might Environmental and biotic stresses might prompt applesnails to increase their prompt applesnails to increase their consumption of resources, thus exacerbating consumption of resources, thus exacerbating their impact on community and ecosystem their impact on community and ecosystem dynamics. dynamics. Hatchling exhibited predator-specific Hatchling exhibited predator-specific alarm response to cues. This agrees with alarm response to cues. This agrees with literature showing differential responses literature showing differential responses by other freshwater snails ( by other freshwater snails ( Physella Physella ; Turner ; Turner et al. 2000). et al. 2000). Despite high consumption, redear sunfish Despite high consumption, redear sunfish failed to show a feeding preference between failed to show a feeding preference between Planorbella Planorbella or or Pomacea Pomacea , suggesting that , suggesting that sunfish would be unlikely to suppress sunfish would be unlikely to suppress applesnail populations in the field. applesnail populations in the field. Applesnails indicated sensitivity to high Applesnails indicated sensitivity to high density and the presence of crushed density and the presence of crushed conspecifics, suggesting perhaps some conspecifics, suggesting perhaps some ecological weaknesses as an invader. ecological weaknesses as an invader. Eichhornia Eichhornia failed to provide a refuge for failed to provide a refuge for applesnails but other macrophytes in the applesnails but other macrophytes in the field might enhance their ability to avoid field might enhance their ability to avoid predation. predation. Overall, more research on basic ecology Overall, more research on basic ecology of the CAS complex is necessary to predict of the CAS complex is necessary to predict their impact or curb their spread their impact or curb their spread ( ( Estebenet & Martín Estebenet & Martín 2000). 2000). Rebecca K. Marfurt, Brandon B.Boland and Dr. Romi L. Burks Rebecca K. Marfurt, Brandon B.Boland and Dr. Romi L. Burks Department of Biology, Southwestern University, Georgetown, TX 78626 Department of Biology, Southwestern University, Georgetown, TX 78626 For more information about applesnail research, please contact For more information about applesnail research, please contact [email protected] In native habitats, channeled applesnails (Pomacea canaliculata) graze periphyton. However, casual observations from introduced populations suggest these invaders show variation in feeding ecology, predator response and life history strategies. Attempts to predict this consumer influence on ecosystem function suffer from a lack of basic data. We tested how salinity affected snail mortality. Both adults and hatchlings tolerated salinity levels up to 8 ppt. Adult feeding on lettuce increased significantly at 8 ppt compared to 0 ppt (p = 0.002), while hatchling consumption of algae did not vary (p = 0.284). To see how these consumers responded to predators from the invaded ecosystem, we tested behavioural responses to predatory cues from fish, turtles, crayfish and adult applesnails. Results indicated that fish and crayfish prompted similar predator-avoidance behaviors in hatchlings (p’s < 0.05) and that hatchling response changed over time. Consumption rates of juvenile and redear sunfish did not vary (Χ 2 , p > 0.05) between native (ramshorn) and exotic applesnails. We recently found that the presence of sunfish enhanced consumption by adult snails when presented alone, but depressed consumption in combination with conspecific cues. Juveniles did show signs of intraspecific competition. Research providing insight into the basic ecology of applesnails can foster management efforts at the ecosystem scale. 1 1 2 2 3 3 4 4 Contrasting mechanisms and feeding preferences of exotic (Texas) vs. native (Uruguay) populations of applesnails. Investigating plant preference and deterrence in different life history stages of applesnails. Examining the successful transition of applesnails from egg to hatchlings to juveniles under different environmental conditions (temperature, salinity, predator cues). Developing a predictive regression model for estimating abundance of applesnails in the field based on egg masses. EXPERIMENT 1 – SALINITY IMPACTS: EXPERIMENT 1 – SALINITY IMPACTS: We exposed either 1 adult or 6 hatchling applesnails instantaneously (i.e. no acclimation) to 4 levels of salinity ranging from 0 ppt – 35 ppt (N=4). Adults fed on lettuce and hatchlings consumed algae off tiles. We recorded percent consumption of the resources. EXPERIMENT 2 – PREDATOR RESPONSE: EXPERIMENT 2 – PREDATOR RESPONSE: We exposed groups of 6 hatchling applesnails (N=6) to 1 of 5 predatory chemical cue treatments (incubated 17-L for 12 hrs): 1) no cues; 2) turtle; 3) sunfish; 4) adult applesnail; or 5) crayfish; and observed alarm responses (burying or crawling out) after 60 minutes. EXPERIMENT 3 – PREDATOR AGE-SPECIFIC EXPERIMENT 3 – PREDATOR AGE-SPECIFIC PREFERENCE: PREFERENCE: We fed adult or juvenile redear sunfish (Lepomis microlophus ) juvenile applesnails, native ramshorn snails (Planorbella) or both types for nine days (N=3) to test each prey choice with fish size (N=3). We then recovered the remaining snails after 2 hrs of predation. EXPERIMENT 4 – REFUGE EFFECT: EXPERIMENT 4 – REFUGE EFFECT: Groups of 6 snails occurred in a 2x2 experimental design (N=4) in the presence or absence of redear sunfish as the predator and water hyacinth (Eichhornia crassipes ) as the refuge. We recorded mortality after 24 hrs. EXPERIMENT 5a & 5b – RESOURCE EXPERIMENT 5a & 5b – RESOURCE CONSUMPTION IN PRESENCE OF PREDATORY CUES: CONSUMPTION IN PRESENCE OF PREDATORY CUES: We tested per gram consumption rates of adult applesnails in A) the presence of fish cue (1 L from redear sunfish tank into 9 L distilled) and in B) the presence of fish cue plus cues from crushed-up conspecifics (i.e. other applesnails). In a 2x2 design (N=4), snails fed for 4 hrs on either green leaf lettuce or Myriophyllum spicatum (Eurasian water milfoil, chemically defended) in the presence or absence of predatory cues. We calculated a consumption ratio of grams of plant consumed per grams of applesnails. EXPERIMENT 6 – INTRASPECIFIC COMPETITION EXPERIMENT 6 – INTRASPECIFIC COMPETITION AND RESOURCE CHOICE: AND RESOURCE CHOICE: We studied the impacts of snail density (1 vs. 3 snails in containers measuring 36 x 25 x 13 cm) and lighting (constant light vs. dark) on the juvenile applesnail consumption of two resources: lettuce versus purple cabbage. Four trials took place over a span of 7 days and we averaged the per capita consumption rates. We predicted that Crawlin g out Buried Sunfish Crayfis h Turtle Adult Applesna il Cue Water Control: No cue Each Results figure refers to Experiment # in Methods A B C The channeled applesnail (CAS – Photo A; Photo A; Pomacea “canaliculata” ) made the list of the Top 100 invasive species (ISSG 2004) and has restricted status in Texas. Species-specific identity within the complex“canaliculata” leaves room for much debate in this group of applesnails (B. Howells, personal communication), making differences in life history all the more interesting. CAS exhibit high fecundity rates, laying up to 3000 eggs/clutch (Marfurt, unpublished data). Such high reproduction generally increases success of exotic species (Lodge 1993). To reduce predation, adults lay eggs above the water’s surface usually on plants ( ( Photo B Photo B ); ); Hatchlings ( ( Photo C Photo C ) ) drop into the water where they confront predators. CAS voraciously consumer aquatic macrophytes (Estoy et al. 2002), and possess the potential to invade systems with varying salinity, including freshwater ponds and lakes. Seen as a generalist feeder, CAS may be very destructive to wetland habitats and possibly cause a decline in native plants and animals (Lach et al. 2000). Recent research, however, calls into question the generalist nature of this highly destructive herbivore (Lach et al. 2000) and more studies that investigate factors that influence feeding may add to our power to predict impacts. Exotic, invasive species pose a real threat to biodiversity, especially in small lakes & ponds (Sala et al. 2000). Thus, research focused in this area may help prevent ecosystem degradation or promote restoration. September 2004: September 2004: Background picture Background picture shows students shows students conducting field conducting field surveys of applesnails surveys of applesnails at Horsepen Bayou near at Horsepen Bayou near Houston. Houston. 1. Estebenet A. L. & Martín P. R. 2002. Pomacea canaliculata (Gastropoda: Ampullariidae): Life history traits and their plasticity. Biocell 26(1): 83-89. 2. Estoy et al. 2002. Effects of food availability and age on the reproductive effort of the apple snail, Pomacea canaliculata. Appl. Ent. Zoology 4: 543-550. 3. Invasive Species Specialist Group (ISSG). 2004. 100 of the world’s worst alien species. http:// wwww.issg.org/booklet.pdf . 4. Lach et al. 2000. Food preference and reproductive plasticity in an invasive freshwater snail. Biological Invasions 2: 279-288. 5. Lodge D. M. 1993. Biological invasions: lessons for ecology. TREE 8: 133-137. 6. Sala et al. 2000. Biodiversity scenarios for the year 2100. Science 287: 1770-1774. 7. Turner et al. 2000. Chemical cues modify species interactions: the ecological consequences of predator avoidance by freshwater snails. Oikos 88(1): 148-158. REFERENCES REFERENCES We would like to thank Bob Howells (TPWD), Mark Kramer and Ann Brinley (Armand Bayou), and Southwestern University for supporting this research. Ecology students Kim Boyd, Matthew Garcia and Cody Freas provided the intraspecific competition data. 5a 5a 5b 5b 1-mm 6 6 #587 #587
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Transcript of LIFE HISTORY VARIATION IN INVADING APPLESNAILS (“POMACEA CANALICULATA”) MAY POSE ECOLOGICAL...
LIFE HISTORY VARIATION IN INVADING APPLESNAILS LIFE HISTORY VARIATION IN INVADING APPLESNAILS (“(“POMACEA CANALICULATA”POMACEA CANALICULATA”) MAY POSE ECOLOGICAL THREAT ) MAY POSE ECOLOGICAL THREAT
TO WETLANDS TO WETLANDS
INTRODUCTIONINTRODUCTION
ABSTRACTABSTRACT METHODSMETHODS RESULTRESULTSS
DISCUSSIONDISCUSSION
FUTURE FUTURE PLANSPLANS
In our experiments, exotic, invasive, In our experiments, exotic, invasive, channeled applesnails demonstrated their: 1) channeled applesnails demonstrated their: 1) ability to respond to predators; 2) capability ability to respond to predators; 2) capability of surviving moderate environmental stress; of surviving moderate environmental stress; 3) sensitivity to intraspecific competition; 4) 3) sensitivity to intraspecific competition; 4) and their susceptibility to predation by native and their susceptibility to predation by native predators.predators.
With their reproductive capacities, With their reproductive capacities, generalist feeding, and genetic diversity, CAS generalist feeding, and genetic diversity, CAS represent a serious ecological threat to represent a serious ecological threat to estuarine and freshwater systems.estuarine and freshwater systems.
P. “canaliculata” P. “canaliculata” did not survive salinity did not survive salinity levels >14ppt. Thus, storm surges typical of levels >14ppt. Thus, storm surges typical of tropical storms or hurricanes could damage tropical storms or hurricanes could damage applesnail populations in estuarine systems. applesnail populations in estuarine systems. However, none of our results indicated that However, none of our results indicated that the snails would not thrive in freshwater the snails would not thrive in freshwater systems as well.systems as well.
Environmental and biotic stresses might Environmental and biotic stresses might prompt applesnails to increase their prompt applesnails to increase their consumption of resources, thus exacerbating consumption of resources, thus exacerbating their impact on community and ecosystem their impact on community and ecosystem dynamics.dynamics.
Hatchling exhibited predator-specific alarm Hatchling exhibited predator-specific alarm response to cues. This agrees with literature response to cues. This agrees with literature showing differential responses by other showing differential responses by other freshwater snails (freshwater snails (PhysellaPhysella; Turner et al. ; Turner et al. 2000).2000).
Despite high consumption, redear sunfish Despite high consumption, redear sunfish failed to show a feeding preference between failed to show a feeding preference between PlanorbellaPlanorbella or or PomaceaPomacea, suggesting that , suggesting that sunfish would be unlikely to suppress sunfish would be unlikely to suppress applesnail populations in the field. applesnail populations in the field.
Applesnails indicated sensitivity to high Applesnails indicated sensitivity to high density and the presence of crushed density and the presence of crushed conspecifics, suggesting perhaps some conspecifics, suggesting perhaps some ecological weaknesses as an invader.ecological weaknesses as an invader.
Eichhornia Eichhornia failed to provide a refuge for failed to provide a refuge for applesnails but other macrophytes in the applesnails but other macrophytes in the field might enhance their ability to avoid field might enhance their ability to avoid predation. predation.
Overall, more research on basic ecology of Overall, more research on basic ecology of the CAS complex is necessary to predict their the CAS complex is necessary to predict their impact or curb their spread (impact or curb their spread (Estebenet & Estebenet & MartínMartín 2000). 2000).
Rebecca K. Marfurt, Brandon B.Boland and Dr. Romi L. BurksRebecca K. Marfurt, Brandon B.Boland and Dr. Romi L. BurksDepartment of Biology, Southwestern University, Georgetown, TX 78626Department of Biology, Southwestern University, Georgetown, TX 78626
For more information about applesnail research, please contact For more information about applesnail research, please contact [email protected]
In native habitats, channeled applesnails (Pomacea canaliculata) graze periphyton. However, casual observations from introduced populations suggest these invaders show variation in feeding ecology, predator response and life history strategies. Attempts to predict this consumer influence on ecosystem function suffer from a lack of basic data. We tested how salinity affected snail mortality. Both adults and hatchlings tolerated salinity levels up to 8 ppt. Adult feeding on lettuce increased significantly at 8 ppt compared to 0 ppt (p = 0.002), while hatchling consumption of algae did not vary (p = 0.284). To see how these consumers responded to predators from the invaded ecosystem, we tested behavioural responses to predatory cues from fish, turtles, crayfish and adult applesnails. Results indicated that fish and crayfish prompted similar predator-avoidance behaviors in hatchlings (p’s < 0.05) and that hatchling response changed over time. Consumption rates of juvenile and redear sunfish did not vary (Χ2, p > 0.05) between native (ramshorn) and exotic applesnails. We recently found that the presence of sunfish enhanced consumption by adult snails when presented alone, but depressed consumption in combination with conspecific cues. Juveniles did show signs of intraspecific competition. Research providing insight into the basic ecology of applesnails can foster management efforts at the ecosystem scale.
11 22
33 44
Contrasting mechanisms and feeding preferences of exotic (Texas) vs. native (Uruguay) populations of applesnails.
Investigating plant preference and deterrence in different life history stages of applesnails.
Examining the successful transition of applesnails from egg to hatchlings to juveniles under different environmental conditions (temperature, salinity, predator cues).
Developing a predictive regression model for estimating abundance of applesnails in the field based on egg masses.
EXPERIMENT 1 – SALINITY IMPACTS:EXPERIMENT 1 – SALINITY IMPACTS: We exposed either 1 adult or 6 hatchling applesnails instantaneously (i.e. no acclimation) to 4 levels of salinity ranging from 0 ppt – 35 ppt (N=4). Adults fed on lettuce and hatchlings consumed algae off tiles. We recorded percent consumption of the resources.
EXPERIMENT 2 – PREDATOR RESPONSE:EXPERIMENT 2 – PREDATOR RESPONSE: We exposed groups of 6 hatchling applesnails (N=6) to 1 of 5 predatory chemical cue treatments (incubated 17-L for 12 hrs): 1) no cues; 2) turtle; 3) sunfish; 4) adult applesnail; or 5) crayfish; and observed alarm responses (burying or crawling out) after 60 minutes.
EXPERIMENT 3 – PREDATOR AGE-SPECIFIC EXPERIMENT 3 – PREDATOR AGE-SPECIFIC PREFERENCE:PREFERENCE: We fed adult or juvenile redear sunfish (Lepomis microlophus) juvenile applesnails, native ramshorn snails (Planorbella) or both types for nine days (N=3) to test each prey choice with fish size (N=3). We then recovered the remaining snails after 2 hrs of predation.
EXPERIMENT 4 – REFUGE EFFECT:EXPERIMENT 4 – REFUGE EFFECT: Groups of 6 snails occurred in a 2x2 experimental design (N=4) in the presence or absence of redear sunfish as the predator and water hyacinth (Eichhornia crassipes) as the refuge. We recorded mortality after 24 hrs.
EXPERIMENT 5a & 5b – RESOURCE EXPERIMENT 5a & 5b – RESOURCE CONSUMPTION IN PRESENCE OF PREDATORY CONSUMPTION IN PRESENCE OF PREDATORY CUES:CUES: We tested per gram consumption rates of adult applesnails in A) the presence of fish cue (1 L from redear sunfish tank into 9 L distilled) and in B) the presence of fish cue plus cues from crushed-up conspecifics (i.e. other applesnails). In a 2x2 design (N=4), snails fed for 4 hrs on either green leaf lettuce or Myriophyllum spicatum (Eurasian water milfoil, chemically defended) in the presence or absence of predatory cues. We calculated a consumption ratio of grams of plant consumed per grams of applesnails.
EXPERIMENT 6 – INTRASPECIFIC EXPERIMENT 6 – INTRASPECIFIC COMPETITION AND RESOURCE CHOICE:COMPETITION AND RESOURCE CHOICE: We studied the impacts of snail density (1 vs. 3 snails in containers measuring 36 x 25 x 13 cm) and lighting (constant light vs. dark) on the juvenile applesnail consumption of two resources: lettuce versus purple cabbage. Four trials took place over a span of 7 days and we averaged the per capita consumption rates. We predicted that lettuce would be the preferred food.
Crawling out
BuriedSunfish Crayfish
TurtleAdult
Applesnail
Cue Water
Control: No cue
Each Results figure refers to Experiment # in Methods
A B C
The channeled applesnail (CAS – Photo Photo A;A; Pomacea “canaliculata”) made the list of the Top 100 invasive species (ISSG 2004) and has restricted status in Texas.
Species-specific identity within the complex“canaliculata” leaves room for much debate in this group of applesnails (B. Howells, personal communication), making differences in life history all the more interesting.
CAS exhibit high fecundity rates, laying up to 3000 eggs/clutch (Marfurt, unpublished data). Such high reproduction generally increases success of exotic species (Lodge 1993). To reduce predation, adults lay eggs above the water’s surface usually on plants ((Photo BPhoto B);); Hatchlings ((Photo CPhoto C)) drop into the water where they confront predators.
CAS voraciously consumer aquatic macrophytes (Estoy et al. 2002), and possess the potential to invade systems with varying salinity, including freshwater ponds and lakes.
Seen as a generalist feeder, CAS may be very destructive to wetland habitats and possibly cause a decline in native plants and animals (Lach et al. 2000).
Recent research, however, calls into question the generalist nature of this highly destructive herbivore (Lach et al. 2000) and more studies that investigate factors that influence feeding may add to our power to predict impacts.
Exotic, invasive species pose a real threat to biodiversity, especially in small lakes & ponds (Sala et al. 2000). Thus, research focused in this area may help prevent ecosystem degradation or promote restoration.
September 2004:September 2004:Background picture Background picture shows students shows students conducting field conducting field surveys of applesnails surveys of applesnails at Horsepen Bayou near at Horsepen Bayou near Houston. Houston.
1. Estebenet A. L. & Martín P. R. 2002. Pomacea canaliculata (Gastropoda: Ampullariidae): Life history traits and their plasticity. Biocell 26(1): 83-89.
2. Estoy et al. 2002. Effects of food availability and age on the reproductive effort of the apple snail, Pomacea canaliculata. Appl. Ent. Zoology 4: 543-550.
3. Invasive Species Specialist Group (ISSG). 2004. 100 of the world’s worst alien species. http://wwww.issg.org/booklet.pdf.4. Lach et al. 2000. Food preference and reproductive plasticity in an invasive freshwater snail. Biological Invasions 2: 279-288.5. Lodge D. M. 1993. Biological invasions: lessons for ecology. TREE 8: 133-137. 6. Sala et al. 2000. Biodiversity scenarios for the year 2100. Science 287: 1770-1774. 7. Turner et al. 2000. Chemical cues modify species interactions: the ecological consequences of predator avoidance by freshwater
snails. Oikos 88(1): 148-158.
REFERENCESREFERENCES
We would like to thank Bob Howells (TPWD), Mark Kramer and Ann Brinley (Armand Bayou), and Southwestern
University for supporting this research. Ecology students Kim Boyd, Matthew Garcia and Cody Freas provided the
intraspecific competition data.
5a5a 5b5b
1-mm
66
#587#587
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