Evolutionary and community ecology of nutrient balance for ants

This work examines how resource availability affects the physiological, evolutionary, and community ecology of ants. The foundation for this work is Ecological Stoichiometry (ES) – the study of the balance of resources in ecological systems. Ants serve as an ideal system for ES because they collect diverse foods (nectar, prey, fungus), they have a modular colony structure (which allows for chemical variation to be built through variation among the colony’s brood, workers, and reproductives) and they are diverse and abundant in many ecosystems. We focus on how particular nutrient scarcities or excesses affect the expression of traits that influence ecological interactions. We are currently working with Mike Kaspari (Oklahoma) on a 3-year project funded by the National Science Foundation that is exploring the ecological stoichiometry of litter ant communities on Barro Colorado Island in Panama

Ecological stoichiometry of grassland insects

One of the most important human impact on ecosystems is the alteration of nutrient availability in natural systems. How these alterations affect consumer communities in terrestrial systems has received relatively little attention despite the fact that consumer community composition can substantially influence the structure and stability of local ecosystems. Our work focuses on how specific nutrient inputs affect the composition of grassland insect communities. Part of this work is in connection with NutNet, a global research cooperative exploring the role of nutrient inputs and herbivores on grassland ecosystems.

Interaction of herbivory and fire on ecosystem processes

This research focuses on aboveground-belowground linkages in an oak savanna at the Cedar Creek Ecosystem Science Reserve. This research is in a long-term experimental burn area where variation in fire frequency has generated a gradient of conditions from dense forest to open savanna. Bur oaks at this site are often heavily infested with either lace bugs (Corythuca arcuata) or aphids (Hoplochaithropsus quercicola). Both of these specialists feed with piercing mouthparts and thus their foraging leaves behind intact tissue. We found that feeding by lace bugs results in higher lignin content in litterfall and leads to a subsequent ~25% reduction in litterfall decomposition rate. We also showed that lace bug herbivory is much more common in frequently burned areas than in unburned areas, suggesting that frequent fires promote interactions that decelerate decomposition, which should amplify other influences of fire that slow nitrogen cycling.

Phosphorus limitation and the maintenance of sex

Our work, conducted in collaboration with Maurine Neiman (University of Iowa) has led to a novel hypothesis for the maintenance of sexual reproduction in natural populations. Because only females contribute directly to the rate of population growth, the production of males by sexual females creates a two-fold cost of sexual reproduction that should theoretically result in the selective elimination of sex. We focus on the material costs of polyploidy, a nearly ubiquitous correlate of asexuality in animals. Polyploidy can provide genetic and physiological benefits, but it may also confer costs. We have proposed that there are costs to higher ploidy associated with greater allocation to phosphorus (P)-rich nucleic acids that will be relevant to the maintenance of sex when asexuals are of higher ploidy level than sexuals. Specifically, this greater allocation to nucleic acids should lead to higher demands for dietary P and increased sensitivity to environmental P scarcity. As a result, competitive outcomes between asexual and sexual organisms that differ in ploidy should be mediated by P availability. The implication is that the “paradox” of sex may be mitigated in some conditions by the specific resource requirements associated with an additional set of chromosomes.

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