Matthew D. Moran

Top-Down Cascade from a Bitrophic Predator in an Old-Field Community

We tested the hypothesis that a bitrophic (third and fourth level) arthropod predator can exert a cascading, top—down influence on other arthropods and plants in an early successional old field. First—stadium mantids, Tenodera sinensis, were added to replicated open—field plots in numbers corresponding to naturally occurring egg hatch density and allowed to remain for

A trophic cascade in a diverse arthropod community caused by a generalist arthropod predator

\approx 2

Short-term responses to elevated predator densities: noncompetitive intraguild interactions and behavior

mo. Sticky—trap dispersal barriers around both control and mantid—addition plots allowed us to monitor emigration of arthropods continuously during the experiment. Biomass of herbivores, carnivores, and plants, and abundances of arthropod taxa within plots were determined at the beginning, middle, and end of the experiment. The impact of mantids on the community was a top—down trophic cascade, beginning at the fourth trophic level and evident at each of the lower three levels. Mantids induced marked behavioral responses in other predators, but inteference among predators did not prevent the trophic cascade. The most common predators, cursorial spiders, emigrated from mantid addition plots in significantly greater numbers than from controls. This behavioral response may have resulted from avoidance of predation or competition. Mantids decreased biomass of herbivorous arthropods through predation, and this decrease in turn increased biomass of plants. Therefore, these generalist predators were able to decrease herbivory enough to affect plant growth. This and other recent studies indicate that top—down effects can be important in structuring terrestrial communities. Ours is the first example of a top—down cascade by a generalist arthropod predator in a nonagricultural ecosystem and illustrates the importance of detecting behavioral responses in studies of trophic interactions.

Seasonal variation in top-down and bottom-up processes in a grassland arthropod community

Abstract We tested the hypothesis that a generalist arthropod predator, Tenodera sinensis Saussure, could trigger a trophic cascade in an old-field ecosystem. These mantids had relatively weak effects on abundance and biomass of other carnivorous arthropods as a group. The effect of mantids on herbivores was stronger than on carnivores, mainly concentrated in Homoptera and Diptera. Herbivore load was reduced by mantids with the consequence that overall plant biomass (mainly grasses) was increased. Percapita interaction strengths between mantids and other arthropod taxa were, for the most part, weakly negative. Our study demonstrates that a significant trophic cascade can be triggered by a generalist predator even within the framework of a diverse community with relatively diffuse interactions.

RELIEVING FOOD LIMITATION REDUCES SURVIVORSHIP OF A GENERALIST PREDATOR

We investigated the short-term response of an arthropod assemblage to elevated generalist predator densities by introducing Chinese mantids (Tenodera sinensis) to field plots in a replicated, controlled experiment. Abundances of carnivorous arthropods were reduced by mantids to a greater extent than herbivores, and cursorial spiders emigrated from treatment plots in greater numbers than from controls. Initially, this emigration consisted only of small spiders that were demonstrated in the laboratory to be prey for mantids. Thus, the initial response of an arthropod assemblage to increased predators, densities was increased interactions among predators, which caused decline in predator population densities in a shorter time than competition for prey would require. Predator avoidance behavior must be considered together with intraguild predation and competition when interpreting the outcome of predator manipulations. Shortterm experiments may be more valuable than longer term studies in detecting this effect.

Community effects of praying mantids: a meta-analysis of the influences of species identity and experimental design

Both top-down and bottom-up processes are common in terrestrial ecosystems, but how these opposing forces interact and vary over time is poorly understood. We tested the variation of these processes over seasonal time in a natural temperate zone grassland, a field site characterized by strong seasonal changes in abiotic and biotic conditions. Separate factorial experiments manipulating nutrients and cursorial spiders were performed in the wet and dry seasons. We also performed a water-addition experiment during the summer (dry season) to determine the degree of water limitation during this time. In the spring, nutrient addition increased plant growth and carnivore abundance, indicating a bottom-up control process. Among herbivores, sap-feeders were significantly enhanced while grazers significantly declined resulting in no net change in herbivore abundance. In the summer, water limitation was predominant increasing plants and all herbivores while nutrient (N) effects were non-significant. Top-down processes were present only in the spring season and only impacted the guild of grazing herbivores. These results show that bottom-up limitation is present throughout the season in this grassland, although the specific limiting resource changes as the season progresses. Bottom-up processes affected all trophic levels and many different guilds, while top-down effects were limited to a select group of herbivores and did not extend to the plant trophic level. Our results show that the relative strengths of top-down and bottom-up processes can shift over relatively short periods of time in habitats with a strong seasonal component.

Bison Grazing Increases Arthropod Abundance and Diversity in a Tallgrass Prairie

We tested the hypothesis that food supplementation for the generalist arthropod predator Tenodera sinensis would alleviate starvation and reduce intraguild predation. Two field experiments showed that mantids had higher growth rates and lower dispersal in the presence of supplemental prey. However, estimated mortality was greater in food-addition plots, so that numbers of mantid nymphs remaining at the end of the experiments were not significantly different from those in control plots. When groups of mantids were raised in the laboratory, mortality declined with increased food, owing to decreased starvation. Cannibalism in these cohorts did not differ between food levels. Therefore, greater mortality at higher food levels probably was not caused by intraspecific interactions. Emigration of cursorial spiders large enough to prey on mantids decreased in the food-addition plots and may have increased intraguild predation on mantids. In any case, elevating prey level apparently does not predictably benefit food-limited generalist predators.

Cuticular Extracts of Five Common Mantids (Mantodea: Mantidae) of the Eastern United States

Abstract  1. Generalist arthropod predators are ubiquitous in terrestrial ecosystems but experimental studies have yielded little agreement as to their effects on prey assemblages. Drawing on results from a suite of experimental field studies, a meta‐analysis was conducted of the impact of praying mantids (Mantodea: Mantidae) on arthropod assemblages in order to identify predictable and unpredictable effects of these extremely generalised predators.

Life History and Population Characteristics of the Mantid Stagmomantis carolina (Mantodea: Mantidae)

ABSTRACT How grazing-induced ecosystem changes by ungulates indirectly affect other consumers is a question of great interest. I investigated the effect of grazing by American Bison (Bos bison L.) on an arthropod community in tallgrass prairie. Grazing increased the abundance of arthropods, an increase that was present in both herbivorous and carnivorous assemblages, but not in detritivores. The increase in herbivores and reduction in plant biomass from grazing resulted in an arthropod herbivore load almost three times higher in grazed plots compared with controls. Among herbivores, the sap-feeding insect guild was dramatically more abundant, while chewing herbivores were not affected. Herbivorous and carnivorous arthropod richness was higher in grazed plots, although the response was strongest among herbivores. Arthropod abundance on individual grasses and forbs was significantly higher in grazed areas, while plant type had no effect on abundance, indicating that the change was ecosystem-wide and not simply in response to a reduction in grass biomass from grazing. The response of arthropods to grazing was strongest in the early part of the growing season. Published research shows that ungulate grazing, although decreasing available biomass to other consumers, enhances plant quality by increasing nitrogen level in plants.Thearthropod results of this study suggest higher plant quality outweighs the potential negative competitive effects of plant biomass removal, although other activities of bison could not be ruled out as the causative mechanism. Because arthropods are extremely abundant organisms in grasslands and a food source for other consumers, bison may represent valuable management tools for maintaining biodiversity.

A Test of Potential Pleistocene Mammal Seed Dispersal in Anachronistic Fruits Using Extant Ecological and Physiological Analogs

We undertook a preliminary investigation of the cuticular extracts of five common mantid species in the eastern United States: Tenodera sinensis (Saussure), T. angustipennis (Saussure) and Mantis religiosa (Linnaeus) introduced from the Old World and Stagmomantis carolina (Johannson) and Bruneria borealis (Scudder), which are New World species. The major components of these mixtures were normal alkanes, predominately hentriacontane, or in the case of the parthenogenic species B. borealis, tritriacontane. Tricontanal was detected in the extracts of all five species, and smaller amounts of other aldehydes and n-tricontanol were detected in some species. Complex mixtures of methyl and dimethylalkanes also were present in these extracts. The composition of the cuticular hydrocarbons of these mantids may be an adaptation for reduction of evaporative water loss in these insects that inhabit open fields.