Disturbance by Fire Frequency and Bison Grazing Modulate Grasshopper Assemblages in Tallgrass Prairie

Abstract

Understanding determinants of local species diversity remains central to developing plans to preserve biodiversity. In the continental United States, climate, grazing by large mammals, fire, and topography are important ecosystem drivers that structure North American tallgrass prairie, with major impacts on plant community composition and vegetation structure. Frequency of fire and grazing by bison (Bos bison), through effects on plant community composition and altered spatial and structural heterogeneity of vegetation in tallgrass prairie, may act as bottom‐up processes that modulate insect community species richness. As previously seen for plant species richness, I hypothesized that grazing had more impact than fire frequency in determining species richness of insect herbivore communities. I examined this prediction with grasshoppers at Konza Prairie, a representative tallgrass prairie site in which fire frequency and bison grazing are manipulated over long terms with landscape‐level treatments. Topographic position (upland vs. lowland) and fire frequency (1‐, 2‐, 4‐year intervals, and unburned) did not significantly influence grasshopper species richness or indices of diversity, while grazing had significant effects. On average, I found ∼45% more grasshopper species and significantly increased values of Shannon H′ diversity at sites with bison grazing. Species abundances were more equally distributed (Shannon's Evenness Index) in grazed sites as well. No significant interactions among burning and grazing treatments explained variation in grasshopper species diversity. Grasshopper species richness responded positively to increased heterogeneity in vegetation structure and plant species richness, and negatively to average canopy height and total grass biomass. Variation in forb biomass did not influence grasshopper species richness. A significant positive relationship between grasshopper species richness and overall grasshopper density was observed. Species richness increased marginally as watershed area of treatments in grazed areas increased, but not in ungrazed areas. Disturbance from ecosystem drivers operating at watershed spatial scales exhibits strong effects on local arthropod species diversity, acting indirectly by mediating changes in the spatial heterogeneity of local vegetation structure and plant species diversity.

Gafanhotos (Orthoptera, Acridoidea) em áreas de cerrados e lavouras na Chapada dos Parecis, Estado de Mato Grosso, Brasil

“…De acordo com Joern (2005), as características do habitat que maximizam a diversidade de gafanhotos incluem a heterogeneidade espacial dos habitats com estrutura aberta, a existência de várias espécies vegetais como fonte de alimento, estrutura heterogênea para os predadores, e espaços que propiciem a termorregulação, além de plantas com alto valor nutritivo, compatível com os cerrados. Pode-se sugerir que a maior riqueza de espécies de gafanhotos nas áreas de cerrados é resultado da estrutura da vegetação uma vez que a diversidade de artrópodes tende a incrementar com o aumento desta estrutura, padrão consistente com a teoria ecológica (Pianka 1966).…”

Orthoptera assemblages associated with macrophytes of floodplain lakes of the Paraná River

“…The species richness in the Orthoptera is determined by a complex relationship between external factors, such as the climate and vegetation, and internal factors, such as population dynamics (Joern 2005;Zhong-Wei et al 2006).…”

“…Although habitat associations with grasshoppers have been studied since the early 1900s (Vestal 1913), understanding patterns of species diversity remains a continuing challenge in grasshopper ecology (Torrusio et al 2002;Joern 2005). Many studies have examined the relationships between grasshopper community composition and vegetation patterns in grassland ecosystems worldwide (Kemp et al 1990;Fielding & Brusven 1993;Sanchez & de Wysiecki 1993;Torrusio et al 2002;Joern 2005;Branson 2011), but the relationships between the Orthoptera and macrophytes in floodplain environments are scarcely known.…”

Introduction to the grasslands and grassland arthropods of Canada

“…Hence, their population dynamics are not driven by changes in the availability of a few species of plants. The populations of most species are highly variable, which reflects factors of weather, fire, grazing, and differences in land use (Gage and Mukerji 1977;Joern 2005;Powell et al 2007). The frequency of Fig.…”