Academic journal article The American Midland Naturalist

Grassland Botanical Structure Influences Lek Spatial Organization in Gryllotalpa Major S. (Orthoptera: Gryllotalpidae)

Academic journal article The American Midland Naturalist

Grassland Botanical Structure Influences Lek Spatial Organization in Gryllotalpa Major S. (Orthoptera: Gryllotalpidae)

Article excerpt

ABSTRACT.-The prairie mole cricket (Gryllotalpa major Saussure) is a rare endemic of the tallgrass prairie ecosystem of the south central United States. Males advertise for females using a low frequency acoustic signal from surface burrows aggregated in leks, but much of the spatial variation observed within the lek remains unexplained. This study reports on the relationship between male spacing and grassland habitat structure within the display arena. The data suggest that as grass heights increase within the lek arena, advertising males increase the distance between their burrows and increase the angle of the surface opening of the burrow. The positive correlation between biomass and spacing was not also seen between biomass and angle of the burrow opening. Prairie mole cricket males, thus, exhibit a form of behavioral plasticity that may have evolved in response to the dynamic disturbance regimes that form and maintain the tallgrass prairie ecosystem.

INTRODUCTION

Grasslands once dominated much of the North American landscape from Central Canada to Northern Mexico, covering nearly fifty percent of the land surface of over 400 million ha. Due to the rich loamy soils that form the basis of these grasslands, extensive agricultural development has rendered the tallgrass prairie ecosystem one of the most fragmented and endangered in all of North America, and anthropogenic forces continue to threaten many endemic grassland species (Axelrod, 1985; Howe, 1994; Joern and Keeler, 1995; Collins, 2000; Collins et al, 2002; Copeland, 2002). Small remnants of tallgrass prairie are now located discontinuously within the historic range in regions of Iowa, Illinois, Missouri and Arkansas, whereas larger remnants are found in the flint hills of Kansas and Oklahoma (Joern and Keeler, 1995; Brye et al, 2002; Copeland, 2002). Understanding how endemic species respond to habitat fragmentation and shifts in changes in land use is of vital importance to attempts to maintain biodiversity and ecological balance of these systems, but in many cases we have yet to learn how endemic species respond to the environmental stochasticity inherent to a naturally functioning tallgrass prairie ecosystem.

Historically, tallgrass prairie ecosystems have had high occurrences of fire and grazing (Axelrod, 1985). Fire is known to inhibit the expansion of woody shrubs and trees into tallgrass prairie along the prairie-forest ecotone (Abrams et al, 1986; Abrams and Hulbert, 1987; Collins, 2000; Briggs el al, 2002) while reducing the accumulation of detritus, releasing nutrients back into the soil and influencing the structure of insect communities (Knapp and Seastedt, 1986; Johnson and Matchett, 2001; Brye et al, 2002). Grazing by bison and other native herbivores likewise affects nutrient redistribution and influences the structure of above ground biomass that is characterized by the seasonal dieback of vegetation that may reach 2 m in height by the end of the growing season (Finck et al, 1993; Collins et al, 1998; Dennis et al, 1998; Fuhlendorf and Engle, 2001; Matlack et al, 2001; Fay, 2003; Harrison et al, 2003; Joern, 2004; Trager et al, 2004;Joern, 2005). These interactive disturbance effects within the ecosystem combine to produce a highly variable deuitus layer and grass height matrix across the landscape. Since acoustically advertising animals such as orthopterans are known to space themselves to optimize the Uansmission and reception of their signals with respect to the above ground botanical elements that characterize the advertising site (Römer, 1993), of special interest is whether or not species that have coevolved in such a stochastic environment as the tallgrass prairie are actually able to respond to changes in above ground habitat structure.

Fire and grazing have been reported to affect insect populations primarily tìirough disturbance and changes in grassland floral assemblages (Bock and Bock, 1991; Siemann and Haarstad, 1997; Kerstyn and Sthing, 1999; Swengel, 2001; Bieringer, 2002; Jonas et al, 2002; Fay, 2003; Joern, 2004; Vermene et oí, 2004; Joern, 2005). …

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