Prairie Insect Conservation
Ideas of February, 2002
Andrew H. Williams
1. Scale: People lacking entomological training often cannot grasp the issue of scale, and so fail to understand what biodiversity conservation really means.
A. Size of organisms: Most insects are vanishingly small in size
B. Number of species: Insects are much more speciose than either vertebrates or plants — 70% of all animal species are insects, 28% of all animal species are beetles.
C. Variety of lifestyles: very much more diverse than among vertebrates
D. Population levels of different species: Huge populations of many insects occur in even tiny spaces, as in 1 cubic meter of prairie vegetation
E. Identity crisis: Identifying vertebrates is a snap, identifying plants is quite easy, but identifying most local insects is still impossible or extremely difficult
2. Seven ways that certain insects may be limited to prairie habitat
A. Food plant specificity of some herbivores
B. Host specificity of some parasites and parasitoids
C. Prey specificity of some predators
D. Plants requiring specific pollinators, and pollinators requiring specific plants
E. Fauna needing grassy structure, including grassy litter
F. Prairie soils are often deep and relatively full of living and dead roots, providing microhabitats needed by some soil fauna
G. Fauna restricted to the burrows of prairie mammals
3. Diversity of available resources generally corresponds with the diversity of the insect fauna.
A. Plant species diversity
B. Nectar availability: Very many adult insects use nectar to fuel themselves, regardless of what the young feed upon.
C. Prey/host availability
a. wet – dry spectrum
b. range of litter depths
c. range of vegetation heights
d. range of soil types
e. range of soil depths
f. erosion is not bad, per se. Many Hymenoptera build their nests in slumping banks and in flat spots of bare soil, as along mammal paths
E. Effects of management activities
a. Homogenization of microhabitats threatens biodiversity -mowing, fire and heavy grazing all greatly reduce the microhabitats available to insects. Light and intermittent grazing increases microhabitat diversity, as does partial and random mowing, as do small burn units or the partial burning of large burn units.
b. Apply island biogeographic theory — most remaining patches of any wild habitat, especially prairie, are tiny islands in a sea of human development. The gradual loss of species from any habitat patch is very likely. Our present ability to successfully reintroduce prairie-restricted animals to sites from which they have disappeared is in its absolute infancy, and of most such taxa we are, as yet, totally unaware.
c. Herbicides — Though herbicides are certainly a useful prairie management tool, there must be some risk to some animals, to soil fauna especially, associated with their use. Probably many animals cannot survive being bathed in one or several herbicides.
d. Combining management tools, as by using fire followed by grazing, or by applying different grazing mammals intermittently, or by fire followed by partial mowing focused for brush control, or by cutting brush followed by spot foliar herbicide application of re-sprouts, etc., will likely accomplish more than use of any such tool in isolation. I believe fire is a fun and relatively inexpensive tool that is generally used too much — used too often and used over too much of a given remnant. Grazing, on the other hand, is a tool often completely ignored.
e. Prairie is not neat; it’s not uniform. Our job is never done but is always ongoing. Don’t expect to kill all the brush, as it cannot and probably should not be done. Our job is to control brush. Think in terms of gray, rather than in black and white.
Vigorous application of any of the tools of prairie management must be detrimental to some of the species present. Only by moderating our management activities — by spreading the risk inherent in any of them over time and space — can we maximize our chances of success in our efforts to manage islands of wild land for biodiversity conservation, given our ignorance of the majority of fauna present on any site.