1)
The effects of consumer diversity in temporary pond communities
Although
a great deal of work has examined how diversity loss within plant communities
affects ecological systems, there has been much less work directed at
examining how diversity loss of consumer species affects ecological systems.
Furthermore, most studies of diversity loss often assume that species
are lost at random. With the assistance of a grant from the National Science
Foundation, our lab is currently focusing on how non-random patterns of
diversity loss within consumer trophic levels affects ecological processes
operating within temporary pond communities. The consumer species that
we are focusing on include aquatic predatory insects and grazing larval
frogs. To explore the effects of diversity loss within both predator and
herbivore trophic levels, we are conducting a survey of temporary ponds
in the coastal plain of North Carolina and conducting a series of experiments
in artificial ponds.
2) Determinants
of interaction strength in food webs
Interactions
among species play an important role in controlling both community structure
and the population dynamics of individual species. We have shown that
variation in the identity of top predators (different species of fish
and salamanders) that occur in pond food webs can alter how strongly the
top predator trophic position interacts with prey species (larval frogs
and toads). Furthermore, we have examined how easily identifiable characteristics
(e.g., body size, traits associated with taxonomic affiliation, and microhabitat
use) of a predator affects how strongly a predator species interacts with
its prey. We have also evaluated how well allometric models of metabolic
rate predict the impact of predator populations on their prey when the
predator populations differ in abundance and average body size. Our work
also examines the influence of the abiotic environment on species interactions.
Previously, Chalcraft worked with Robin Andrews to demonstrate that rates
of predation on lizard eggs by ants on Barro Colorado Island in Panamavaries
with the amount of rainfall. Such variation in the rate of predation likely
explains long-term fluctuations in the population size of the tropical
lizard, Anolis limifrons.
Most
recently, Tracy Rogers and Chalcraft explored how pond hydroperiod affects
the intensity of intraspecific and interspecific competitive interactions
of larval squirrel (Hyla squirella) treefrogs and larval southern toads
(Bufo terrestris). Jon Davenport and Chalcraft are currently studying
intraguild predation between larval dragonflies and larval salamanders
to explain how intermediate predators coexist with top predators. In conjunction
with a number of other students, Chalcraft is also examining how the timing
of community assembly affects the intensity of species interactions.
3) Scale
dependent patterns in biodiversity
How does productivity and nitrogen enrichment affect species diversity?
Does this effect depend on the spatial scale of study? Chalcraft has worked
in collaboration with a number of other scientists to address these questions
by conducting meta-analytical studies of data collected in herbaceous
plant communities at long-term ecological research sites. We have found
that productivity has little influence on the number of species occupying
small study plots but that large areas with intermdiate productivity levels
have more species than large areas having either low or high productivity.
The change in the pattern of how productivity affects the number of species
present with an increase in spatial scale was the result of how productivity
influences beta diversity; the extent of among plot variation in species
composition. Specifically, regions with intermediate productivity tended
to be composed of localities that were very different in their species
composition while regions with low or high productivity are composed of
localities that are more similar in their species composition. In a separate
study, we have found that nitrogen enrichment poses a threat to diversity
loss in herbaceous plant communities at both small and large spatial scales
but that small scale studies may over or underestimate the extent of diversity
loss at larger spatial scales if they fail to consider how nitrogen enrichment
affects beta diversity. Specifically, we found that nitrogen enrichment
causes localities that occur in less productive areas to become more dissimilar
in their species composition while nitrogen enrichment causes localities
that occur in more productive areas to become less dissimilar in their
species composition. Consequently, we found many instances where the increase
in beta diversity following nitrogen enrichment can minimize the extent
of species loss at large spatial scales despite reductions in the number
of species that occur in small localities. Currently, Chalcraft is investigating
how species diversity affects the stability of herbaceous plant communities.
Although
a great deal of work has examined how diversity loss within plant communities
affects ecological systems, there has been much less work directed at
examining how diversity loss of consumer species affects ecological systems.
Furthermore, most studies of diversity loss often assume that species
are lost at random. With the assistance of a grant from the National Science
Foundation, our lab is currently focusing on how non-random patterns of
diversity loss within consumer trophic levels affects ecological processes
operating within temporary pond communities. The consumer species that
we are focusing on include aquatic predatory insects and grazing larval
frogs. To explore the effects of diversity loss within both predator and
herbivore trophic levels, we are conducting a survey of temporary ponds
in the coastal plain of North Carolina and conducting a series of experiments
in artificial ponds.
Interactions
among species play an important role in controlling both community structure
and the population dynamics of individual species. We have shown that
variation in the identity of top predators (different species of fish
and salamanders) that occur in pond food webs can alter how strongly the
top predator trophic position interacts with prey species (larval frogs
and toads). Furthermore, we have examined how easily identifiable characteristics
(e.g., body size, traits associated with taxonomic affiliation, and microhabitat
use) of a predator affects how strongly a predator species interacts with
its prey. We have also evaluated how well allometric models of metabolic
rate predict the impact of predator populations on their prey when the
predator populations differ in abundance and average body size. Our work
also examines the influence of the abiotic environment on species interactions.
Previously, Chalcraft worked with Robin Andrews to demonstrate that rates
of predation on lizard eggs by ants on Barro Colorado Island in Panamavaries
with the amount of rainfall. Such variation in the rate of predation likely
explains long-term fluctuations in the population size of the tropical
lizard, Anolis limifrons.
Most
recently, Tracy Rogers and Chalcraft explored how pond hydroperiod affects
the intensity of intraspecific and interspecific competitive interactions
of larval squirrel (Hyla squirella) treefrogs and larval southern toads
(Bufo terrestris). Jon Davenport and Chalcraft are currently studying
intraguild predation between larval dragonflies and larval salamanders
to explain how intermediate predators coexist with top predators. In conjunction
with a number of other students, Chalcraft is also examining how the timing
of community assembly affects the intensity of species interactions.