Effects of ecological management on tallgrass prairie butterflies and their nectar sources

Abstract

Scope and Method of Study:

The primary goal of my dissertation research was to learn how disturbance-sensitive butterfly species can persist in disturbance-dependent prairie ecosystems. I conducted three studies, all at the same four tallgrass prairies in southwestern Missouri. In Chapter 1, I examine the effects of habitat structure, butterfly species, and butterfly size on butterfly detectability, and the corresponding role of distance sampling in generating better estimates of abundance. In Chapter 2, I examine nectar use and nectar source selectivity of tallgrass prairie butterflies. In Chapter 3, I examine the effects of time since fire, grazing and sampling period on the abundance of Speyeria idalia (an imperiled butterfly) and its nectar sources. Each prairie had two pastures: one rotationally burned and grazed by cattle (also known as pyric herbivory), and one rotationally burned but not stocked with cattle. Butterfly population density and floral resource availability were assessed in early June, late June, and late July of 2006 and 2007.

Findings and Conclusions:

Analyses of distance data revealed substantial variation in butterfly detectability among species and among different behaviors, but not between different habitat structures. I recommend that biologists supplement line transect sampling with distance sampling for butterfly research. Prairie butterfly taxa varied in use of nectar sources. S. idalia showed strong selectivity for a different nectar source during each sampling period. Multiple butterfly taxa were highly selective in for Echinacea pallida. My findings demonstrate the important role that a few subdominant forbs play in conservation of tallgrass prairie butterflies. S. idalia and its nectar sources show complex responses to time since fire, grazing, and sampling period. In 2007, S. idalia population density was a function of a three-way interaction of these factors. Grazing reduced abundance of S. idalia and two preferred nectar sources, Echinacea pallida and Liatris pycnostachya, particularly in recently burned patches. In ungrazed pastures, recent fire appeared to enhance abundance of S. idalia and its preferred nectar sources.