Invasive grass negatively affects growth and survival of an imperiled butterfly

Cs Nordmeyer,S Stapleton,E Runquist

doi:10.3354/esr01136

Abstract

With only ~1% of native prairie remaining in North America, populations of many prairie-obligate species, including the imperiled Dakota skipper butterfly, have drastically declined in recent decades. Unfortunately, population recovery is impeded by an insufficient understanding of Dakota skipper biology. Because larvae have never been naturally observed in the wild, even basic life history elements including preferred host plant(s) are not well understood, and potential hosts have been inferred from grasses inhabiting remnant sites rather than direct observations. To improve our understanding of Dakota skipper biology and habitat needs and inform recovery efforts, we conducted a no-choice performance experiment offering larvae 1 of 5 commonly occurring native grasses and 2 pervasive invasive grass species found across their historic range. We monitored larvae during key life history intervals and evaluated host plant quality by measuring larval and pupal mass, time to pupation, and survivorship. Larvae fed on all offered host grasses, but mass, phenology, and survivorship varied among treatments. Larvae reared on prairie dropseed and porcupine grass had the highest survival, the shortest time to adulthood, and the greatest mass, whereas larvae provided smooth brome and Kentucky bluegrass fared poorly for all observed metrics. All other grasses offered during the study were deemed ‘medium’ quality. Our results suggest that although larvae can feed on a variety of potential host plants, these hosts vary in quality. Invasive grasses across prairies in North America may pose an ecological trap to the conservation of Dakota skipper and other prairie-obligate Lepidoptera.

Highlights

Grasslands are among the most imperiled ecosystems in North America (White et al 2000), with less than 1% of native tallgrass prairies remaining (Samson & Knopf 1994)
These grass species were chosen as they are major dry-mesic prairie grasses co-occurring with Dakota skippers and had either been used in a previous no-choice performance experiment conducted by Dana (1991; Table 2), or were speculated to be used by Dakota skippers in situ
A total of 121 individuals survived to pupation, and we documented variability in the target life history metrics: survival, mass of immature stages, and phenology

Summary

Introduction

Grasslands are among the most imperiled ecosystems in North America (White et al 2000), with less than 1% of native tallgrass prairies remaining (Samson & Knopf 1994). The widespread loss of grasslands over the last century has largely resulted from agricultural conversion and other development (White et al 2000), markedly reducing habitat available to prairie-dependent species and yielding an increasingly fragmented landscape which promotes colonization by non-native plant species (Cully et al 2003). This reduction and degradation of habitat has resulted in the decline of many prairie-obligate species (Leach & Givnish 1996, Brennan & Kuvlesky 2005, Miles & Knops 2009). Non-native plants may pose additional novel threats to imperiled Lepidoptera by creating population sinks and even ecological traps if use of those novel plants as oviposition sites and/or larval hosts is maladaptive (Schlaepfer et al 2005, Keeler & Chew 2008, Yoon & Read 2016)

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Results

Conclusion