Prairie Habitat Fragmentation

Student Research Project
Effects of habitat fragmentation on prairie plant reproduction

Student
Rick Vanderleest
Major: Biology and Engineering
Future Plans: Environmental Engineering

Professor
Steve Hendrix, Professor, Department of Biological Sciences, University of Iowa, Iowa City

In the Midwest, habitat fragmentation and destruction has eliminated over 99.9% of native prairies. As a consequence, many formerly widespread prairie plants are now greatly reduced in abundance. Research in my laboratory is focusing on how reductions in population size and density are affecting reproduction in seven species of prairie forbs (non-grasslike flowering plants). We have chosen to work on these long-lived perennial forbs because they account for about 80% of plant species richness on prairies and because their presence is critical to maintaining prairie biodiversity of higher trophic levels, particularly insects. We hypothesize that reduction in population size of prairie forbs has resulted in negative changes in their ability to reproduce and add new individuals to a population.

The specific hypothesis we are testing is that small populations of prairie forbs, such as those along roadsides and abandoned railroad lines, suffer reduction in fruit and seed set relative to large populations on state preserves because small populations are unable to attract pollinators (mainly butterflies and bees). The first step in our studies is to determine the size, as measured by the number of flowering stems, of 15-25 populations of each species we are studying. In small populations, we can directly count the number of flowering stems; in large populations, we first determine the area occupied and then obtain density estimates by quadrat sample, as Rick is doing in the photo. We collect flowers from each population and count the number of pollen grains on stigmas to determine the degree to which pollen is being moved between flowers in a population. When fruits are matured, we collect about 20 stems from each population and then determine for each stem the number of flowers that were originally present, how many flowers became fully developed fruits, how many fruits aborted, and how many fruits were damaged by insect herbivores.

Our results indicate that in five of the seven species, small populations have reduced fruit set. Furthermore, in these five species, stigmas of flowers from small populations have fewer pollen grains, supporting our hypothesis that pollinators are less likely to find and visit small patches. Observations of butterfly visits to one species of forb (Phlox pilosa) indicate that habitat fragmentation is reducing the diversity and abundance of butterflies. Also, seed germination is reduced in small populations of Phlox, suggesting that inbreeding depression-reduced quality of offspring due to reproduction between closely related individuals-is occurring as a result of habitat fragmentation. The two species in which fruit set is not affected by fragmentation are capable of self-pollination or are pollinated by a wide variety of insects. Our future work will concentrate on quantifying community level changes due to habitat fragmentation in arthropod and plant species diversity of prairies and determining the effects these changes have on community structure and function.

Return to Main Page