What I’m going to present you is part of my masters thesis about joint habitat selection by anuran larvae and predaceous aquatic insects. It is not published yet so I expect to receive a little bit of feedback
Well, predation affects many parameters of community structure, such as [read slide]
Tadpoles are subjected to a wide variety of aquatic predators, specially insects, as you can see in these examples here.
However, much of the joint habitat use by anuran larvae and insects was analyzed at a small scale using laboratory experiments. But little effort has been spent in evaluating how tadpoles and insects select habitats at larger spatial scales. So, one of the key papers that called attention to this issue is from Steven Lima, who pointed out the need to conduct large scale studies to find out how predators and prey respond to each other when selecting habitats
Two bodies of theory predict habitat selection by predators and prey. One of these is game theory that predicts that predators and prey are engaged in a behavioral response race (Sih 1984), adaptatively responding to each other. So from this point of view, there will be two possible results: a negative spatial coincidence between prey and predators indicates that prey have won the behavioral response race, on the other hand a positive spatial coincidence could indicate that predators have won te bebavioral response race. The IFD provides another theoretical perspective on habitat selection, this theory predicts that [reas slide].
So it’s known that females of anurans can select habitats w/o fish and some predaceous insects in order to avoid egg predation. Therefore, this mechanism would produce a checkerboard distribution between insects and tadpoles, and prey would won the behavioral response race
On the other hand, according to the game theory, prey should be spatially constrained by the distribution of their resources, and predators should select prey-rich habitat, leading to a positive spatial coincidence between tadpoles and insects.
Alternatively, both insects and tadpoles could be using similar environmental features when selecting habitats, leading to a concordance between the two communities.
So my question are: [read slide]
The site is located in the highlands of the Serra da Bocaina National Park in southeastern Brazil, near the boundary between the states of São Paulo and Rio de Janeiro.
These are the ponds, you can see that they are pretty variable.
We used the methodology proposed by Azeria and colleagues available in R to test for associations between tadpoles and insects.
We found that the vast majority of associations between insect morphospecies (in row) and tadpoles (in the column) were random.
About 2 percent were negative… Tentar refazer a análise para cada mês.
And finally about 1 percent was positive
Additionally, the two communities were concordant.
And it seems that both communities are being influenced by similar environmental gradients, specially conductivity, turbidity, pond area, and canopy cover. These are CCA analyses for both communities, after removing variables with VIFs above 10.
So the results. Predaceous aquatic insects seem not to influence space use by tadpoles at the metacommunity scale. Some papers in freshwater habitats have found that habitat choice works as a hierarchical process, with prey using different criteria at different scales when selecting habitats. So the fact that we haven’t found fish in ponds we samples could have allowed females to oviposit in that ponds, and then tadpoles would select safe microhabitats within the ponds to avoid predation by insects.
In addition, environmental characteristics seem to influence more habitat selection than predation risk in this systems. Particularly, both tadpoles and insects are being influenced by canopy cover, pond area and pH. So these characteristics appear to be more important for both groups of organisms when selecting habiats.
So to summarize my results, [read the slide], the fact that we did not find any fish inhabiting the ponds could have contributed to this pattern, so insects could not prevent females from ovipositing in ponds, and finally, tadpoles may co-occur with insects and then select safe microhabitats within a pond, in order to avoid predation.
Finally, I want to thank several institutions that supported in several ways this project, be directly providing funding or through fellowships. Other institutions also provided financial support that allowed me to come here to present these results. To end me talk I want to thank you all for coming and I’d happy to answer a few questions. Further questions may be directed to me by email as well. So Thank you!!
Diogo B. Provete Thiago Gonçalves-Souza Denise de C. Rossa-Feres Itamar A. Martins Austin-TX August 2011 [email_address]
Habitat use by predator Habitat Use by prey Sih (1984, 2002) Game theory + Behavioral response race | ∨ Adaptative response Ideal Free Distribution | ∨ Predators aggregate in prey-rich habitats Prey “ wins ” Negative spatial coincidence Predator “ wins ” Positive spatial coincidence
Selection of oviposition site by females Presence of cospecifics or vertebrate/invertebrate predators Checkerboard distribution Prey “ wins ” Resetarits and Wilbur 1989, Skelly 2001 ; Wells 2006
Tadpoles are spatially constrained by the distribution of their resources Introdução____ _____________________________ Predators select habitats with high prey density Positive spatial coincidence Predator “ wins ”
TADPOLES R=0.67 First axis significant Conductivity* Turbidity* Pond Area* * p<0.05 after forward selection considering F-statistics
INSECTS R=0.64 Conductivity* Turbidity* Canopy* * p<0.05 after forward selection considering F-statistics Two first axes significant
Differences in predation risk of Invertebrate vs. vertebrate Predators (Hero et al. , 1998; Gascon, 1992) Habitat choice as a hierarchical process (predation avoidance) (Kramer et al. , 1997) Predaceous insects do not influence habitat use by tadpoles