Invasive plants and native amphibians
Lisa Regula Meyer, Doctoral Candidate
Kent State University
Invasive plants and native amphibians: A study of the possible impacts of Phragmites australis and Typha angustifolia invasions on Lithobates clamitans and L. catebieanus
This project focuses on the differences in habitat structure associated with common reed grass and narrow leaf cattail stands compared with native plant communities, and how those differences affects two closely related species of anurans (Lithobates clamitans and L. catesbeianus). My hypotheses are 1) invaded wetlands have different water chemistries associated with them than non-invaded wetlands; 2) these differences correlate with survivorship and growth of tadpoles in these wetlands; 3) plant chemical profiles relate to different tadpole behaviors; 4) the different physical structure of the wetlands lead to different behaviors in adults; 5) and finally, that wetland differences lead to differing plant and invertebrate communities in the wetlands. While measuring physical and chemical profiles of wetlands types, simultaneous measures of larval anuran (tadpole) growth and survival provide insight into correlations between the abiotic environment and larval characteristics. The studies occurred in natural wetlands representative of each vegetation type and in constructed mesocosms. Further, behavior of larval and adult anurans were observed in the presence of invasive and native plants to assess these effects. These surveys and experiments provide insight into what impacts narrow leaf cattail and common reed grass have on green frogs and bull frogs.
Invasive plants and native amphibians: A study of the possible impacts of Phragmites australis and Typha angustifolia invasions on Lithobates clamitans and L. catebieanus
This project focuses on the differences in habitat structure associated with common reed grass and narrow leaf cattail stands compared with native plant communities, and how those differences affects two closely related species of anurans (Lithobates clamitans and L. catesbeianus). My hypotheses are 1) invaded wetlands have different water chemistries associated with them than non-invaded wetlands; 2) these differences correlate with survivorship and growth of tadpoles in these wetlands; 3) plant chemical profiles relate to different tadpole behaviors; 4) the different physical structure of the wetlands lead to different behaviors in adults; 5) and finally, that wetland differences lead to differing plant and invertebrate communities in the wetlands. While measuring physical and chemical profiles of wetlands types, simultaneous measures of larval anuran (tadpole) growth and survival provide insight into correlations between the abiotic environment and larval characteristics. The studies occurred in natural wetlands representative of each vegetation type and in constructed mesocosms. Further, behavior of larval and adult anurans were observed in the presence of invasive and native plants to assess these effects. These surveys and experiments provide insight into what impacts narrow leaf cattail and common reed grass have on green frogs and bull frogs.
Sigma xi 2013 from Lisa Regula
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This is a very interesting perspective about the factors influencing not only frog growth/survival, but also behavior. I do have some questions about your results. 1) You refer to your results as trends, are any of the relationships significant? 2) Why do you think the invasive plants have different effects on chemistry? 3) If you did a survey of these habitats, what densities of these frogs would you expect? Are frog densities naturally lower in these invasive communities? 4) Why do you think there was no difference in tadpole survival in the habitats in late summer? Could it have to do with the temperature relationship you found? 5) For the adult behavioral trial, where did you get the frogs? Depending on what habitat you got them from, two of the three habitats could be novel to them and may influence behaviors.
ReplyDeleteThanks, I appreciate the encouraging words. I refer to trends because for this set of data, we did not see any significance. Maybe too small a sample size, maybe a bad behavioral design, who knows. It's something I'd like to come back to someday. Both of these particular plants are known to have secondary metabolites with allelopathic capabilities, so there's a chance that these might be changing the water chemistry. Or I might have the cart before the horse, and different water chemistry leads to a different invader (although I doubt it, based on other data from this study that I didn't have enough slides to display). We did do both visual encounter survey and frog call surveys (again, data not presented- dang limits!), and there were differences across the wetland types, lower in invaded wetlands than in native, and I believe lower in Typha, but I'd have to go back and check. We also did surveys of the tadpoles using minnow traps, and they were higher densities away from the invasive plants. The difference between early and late summer is likely either temperature related, or tied to what the plants are doing in their life history (younger plants, earlier in the season, more exudate that could be problematic). It's a question I'd like to investigate further. Adult frogs came from a non-invaded wetland also in Portage County, Ohio, but not used in this study for anything else than as a source of frogs.
DeleteHi Lisa,
ReplyDeleteAs a fellow amphibian conservationist, I am very familiar with the amphibian declines and exciting to see your research. Building on the comments from the previous judge, I had a few additional questions: 1) Are you aware if there is a history of aquatic contamination in the habitats from which theses amphibians were collected? 2) With that, is there a history of chytrid infections? 3) Did you record developmental rates, and if so, were there any effects of your treatment combinations? 4) Do you think 15 minutes for the adult trials was sufficient for acclimation? Is there a precedent for this method?
Overall, very good work!
Thanks! I'm not aware of any aquatic contamination in the cases of the ponds used for these studies, but it is northeastern Ohio, so it is a possibility, unfortunately. There's not been any sign of chytrid so far in the ponds I sampled. Developmental rates did not vary across the treatments, just the size of the individuals. The acclimation time may not have been enough time, and I'd like to try more work with the behavioral arenas. This set up was based on what friends and myself have been able to come up with to test the hypothesis. It's a work in progress.
DeleteHi Lisa,
ReplyDeletethis is very interesting work. Invasive plants obviously affect environmental conditions in a variety of ways. Do you know what specific effects drive differences in tadpoles? Do environmental differences that may drive differential performance of tadpoles vanish in the summer? Also, what do you think are the broad scale implications of your work?
Best wishes, Michi Tobler
Michi,
DeleteThere were some preliminary tadpole behavior tests that we tried with plant extracts showing the tadpoles to have an avoidance reaction to the invasive plants, so I'm thinking that it's mainly chemical in the case of tadpoles, or possibly due to differences in temperature. Most probable solution- it's more than one mechanism of action that affects the tadpoles. I like to think that by adding more information to how invasive plants impact amphibians, we can use that data for management and prioritize how conservation and restoration dollars are spent so that they most benefit amphibians (when the dollars are meant to target amphibians). Whether that results in a preference for un-invaded ponds for conservation priority, or use of conservation funds for removal of invasive plants, or other projects depends on the goals of the managing body, but this- along with the rest of the research going into invasive plant-native amphibian interactions- could at least be more information for managers to base their decisions.
Hello Lisa,
ReplyDeleteReally interesting work! You mentioned that these invasive plants have native relatives. Do you have a sense of how this relatedness might influence the effects of these grasses on the frogs?
Thank you!
Tina,
DeleteIt would be difficult to look at differences between the native relative plants and invasive plants, especially in the case of Phragmites ausstralis. In Ohio at least, the native Phragmites is rare, with ~4 populations left, and classifying it as a separate species (P. communis, likely) or an invasive genotype is the subject of some debate. Kristin Saltonstall's work on the genetics of Phragmites is really interesting, if you want to check out some plant work.
Hi Lisa,
ReplyDeleteYour research project is quite interesting and novel. Amphibians are facing so many threats, I never considered that invasive plant species may be yet another one. I am wondering how you interpret the association of water quality measures with the invasive plant species. It seems that they may be responding to preexisting variation (e.g., more likely to invade certain types of environments) or may be causing the differences. The behavior assays of adult was also quite novel, but I am unsure what to make of it. You showed some fairly big effects of plant species on locomotion, but I'm not sure how to interpret them. For example, is more movement good or bad? It would be very interesting to see what you explore next. Keep up the great research.
Best,
John
John,
DeleteThe correlation/causation conundrum is always difficult, and I'd like to try and tease it out with a long term mesocosm study in the future. The behavior data is difficult to make heads or tails of (or tales, for that matter, because motivation in non-humans is such a black box). I think the invertebrate community really comes into play there, to look at food quality and quantity available to adults, for example. Thanks for the encouragement!
Hi Lisa,
ReplyDeleteThis is a great work, I love your personal video, and the enthusiasm reflected in it. I wouldn't doubt the importance of this work and your success in career. Here I have several personal questions/comments after viewing the presentation.
1) I love the introductory slides. You did a fabulous job here to show and tell the story.
2) Slide 6: I'd like to see the frog somewhere in this diagram.
3) Slide 10: "Week" on the x-axis doesn't seem a helpful way to show the seasonal change, or to make a intuitive connection with the frog development/growth. If I could see how the water quality changes are related to the frogs, it would be much more helpful.
4) It was somewhat unclear how many field sites were tested, how wide/narrow the sites were, whether or not they were good frog habitats, what the sampling technique was, how you followed individual frogs, which time of a day, in a single day or different days, and etc.
5) Slide 17: Not the x-axis title is "day of year", which seems to be better than "week" in the previous slides, however, you should make them consistent to clarify your points. Moreover, the "survival" may give a wrong impression, that the tadpoles were dying out, instead developing into the metamorphosis. It's also unclear which frog species is denoted by which symbols and how the differences were tested. The sample size, replication, and etc. was also not clear in the graph.
6) Slide 20: I'm not sure why you showed all the individual data sets, instead of comparing the different habitats by taking the mean values. I'm not quite sure what biological meanings under a specific context the "movement" or other behavioral parameters that you measured and compared mean.
7) At the end of the presentation, I'd like to see some summary of the results and a kind of conclusion to reflect your findings in the big picture or context.
These are my two cents. Good luck!
I appreciate the kind words about my work; I'm hoping you're right about a successful career. :) I'll try to get through all of the comments. Pictures aren't my strong suit in research- I tend to focus on getting work done, and less on photographing, so the photographs end up as hurried staged photos; my apologies. We recently switched to using day of the year for all graphs, for just the reason you mentioned. In most years, the experiments started around day 140 of the year. Our natural field sites were 8 of each plant type, 10 of each plant type for the large mesocosms, and 5 of each plant type for the kiddie pool mesocosms. They had a wide range of sizes, but were generally around 4 meters in diameter. The sites were all ones that had frog populations there before we added the enclosures, and the animals in the enclosures were not tracked individually. All measures for a given plant type were taken on the same day of each week. Metamorphosis actually wasn't an issue in this case, as green frogs and bull frogs take longer to metamorphose than this study was conducted, and the graphs are not species specific- the early group is green frogs only, but the late group is both green and bull frogs (to compare across species and across time). Also for slide 17, there were approximately 30 tadpoles per enclosure, three enclosures per pond, and 8 ponds per plant type. We were trying to make it possible to track individual animals in the graphs, while showing the means as well. It apparently did not work as we had hoped. Unfortunately, I ran out of slides, and didn't have the space to add summary slide. Thanks!
Delete