FOREST FRAGMENTATION AND ITS EFFECTS ON ARTHROPOD POPULATIONS IN SMALL VS. LARGE FORESTS IN NORTHWEST OHIO Mary C. Baumgardner A Thesis Submitted to the Graduate College of Bowling Green State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE May 2007 Committee: Daniel M Pavuk, Advisor Helen Michaels Rex Lowe ii ABSTRACT Dr. Daniel M. Pavuk, Advisor The loss of biodiversity is a large challenge facing the conservation biologist. Many species of arthropods are susceptible to displacement, starvation or complete decimation when human activities, such as development, occur within or near their habitat. Insects and arthropods are not valued by the average person and are typically considered to be a frightening nuisance. The value of arthropods cannot be overstated. Arthropods perform services for ecosystems that are needed by plants and other organisms. For example, the elimination of insect pollinators would halt much of plant fruit and seed production and cause a reduction in plant repopulation. Detritivorous insects are vital to plants for their distribution of nutrients into soil. Larger forested areas should contain a greater abundance of arthropods and more species than smaller forests, according to the theory of island biogeography. The theory of island biogeography involves the study of distribution of species and community composition on islands. Various patches of small and large forests suggest islands of different sizes (Smith and Smith 2001). I calculated species richness, arthropod abundance and graphed species to forest area comparisons. My nine study sites varied from 1.6 to 1500 hectares. Most of the sites were surrounded by agricultural areas with roads or highways bordering one or more sides of the forests creating a possible barrier. Some of the larger sites also had roads cutting through the forest. Arthropods were sampled four times at each of the nine study sites in late spring and summer of 2005 and 2006 using the beat-stick method for collection. Once arthropods were placed into a zippered plastic bag with the sample of the tree or shrub and preserved in the freezer until sorting and identification could begin. There was little variation in abundance or species richness; small iii forests tended to have only slightly higher abundance numbers than the larger forest sites. The only group of insects that showed greater species richness in small vs. large forests was the order Orthoptera (p<0.05). Sorensen’s Similarity Index showed low similarity in study sites. The results of this study could be useful in land management; more studies need to be completed to aid in the total understanding of species distribution, community structure and optimal habitat requirements for arthropods. iv ACKNOWLEDGEMENTS I would like to express my gratitude to my committee, Dr. Daniel Pavuk, Dr. Helen Michaels, and Dr. Rex Lowe. I would like to thank the Carter family and Bowling Green State University for access to woodlots on their property. I would like to also thank Mr. John Jaeger, Director of Natural Resources of the Metroparks Toledo Area and Mr. Chris Smalley, Stewardship Director, of the Wood County Park District for their permission to complete data collection at Oak Openings, Fuller Preserve, Secor Woods, Bradner Preserve, and Pearson Park. I would also like to thank my friends for their support and understanding. I would like to offer a special thanks to my lab associates, Laura Hughes-Williams, Melanie Bergolc and Rostern Tembo for their assistance, encouragement, compassion, and especially their humor. An extra thank you to Melanie Bergolc for sharing her talents of the computer. Thank you, Helen Michaels, for your guidance with plant identification. Additional thanks to Dr. Dan Pavuk and Rostern Tembo for their assistance in the field, in preparation for this paper. v TABLE OF CONTENTS Section Page INTRODUCTION………………………………………………………………………………...1 METHODS………………………………………………………………………………………..6 RESULTS & ANALYSIS...…………………………………………………….……...………..11 DISCUSSION……………………………………………………………………………………14 LITERATURE CITED………………………………………………………….…...………..…24 TABLES & FIGURES Table # Page 1 TREES & FAMILIES COLLECTED FROM………………………..............................32 (Showing scientific and common name) 2 ORDERS OF ARTHROPODS COLLECTED……………………………...…………..35 (Showing scientific and common names and descriptive terms) 3 WOODLOT NAMES …………………………………………………………....……..36 (Including county location, woodlot size in acres and hectares, number of times collected) 4 SUMMARY OF DIVERSITY INDICES……………………………….…….…..……..37 (Shannon Index and Evenness). 5 SORENSON’S SIMILARITY INDEX SUMMARY TABLE………………..……..…..38 6 SUMMARY TABLE PER DATE……………………………………………….………39 Shannon and Evenness calculations for each collection date) 7 COLLECTION SUMMARY CHART……………………………………......................40 (Site name, area in (ha), total species per site, total arthropod abundance, Shannon Index and Evenness for all collections at that site) (Cont.) vi 8 TWO-SAMPLE T-TEST FOR SMALL VS LARGE FORESTS……………………….41 9 TWO-SAMPLE T-TEST FOR EVENNESS FOR LARGE VS SMALL FORESTS…………………………………………………………………..41 10 TWO-SAMPLE T-TEST FOR TOTAL SPECIES OF LARGE VS SMALL FORESTS……………………………………………………………….…41 11 TWO-SAMPLE T-TEST FOR TOTAL ARTHROPODS OF LARGE VS SMALL FORESTS………………………………………………….…………..41 12 SUMMARY CHART……………………………………………………………....…...42 (Including arthropod order, large or small forest site, mean species richness, standard deviation, standard error mean, P-value and T-value) 13 TREE OR SHRUB COLLECTED FROM & TOTAL ARTHROPODS COLLECTED FROM THAT PLANT SPECIES PER SITE……………………….43 14 CUMULATIVE ARTHROPOD SPECIES LIST PER SITE……………………….…..48 Figure # Page 1 PIE CHART SHOWING PERCENT OF ARTHROPODS COLLECTED AND DIVIDED BY ORDER………………………………………………………...59 2 BAR GRAPHS (A-J), DONE BY ORDER AND COMPARING THE NUMBER PER ODER TO EACH SITE………………………………………...….60 3 FITTED LINE PLOT WITH TOTAL SPECIES VS. HECTARES……………………..65 1 INTRODUCTION “The nature of land-use change in recent decades has not only resulted in a dramatic decrease in total forest cover, but also in an increasingly skewed size-distribution of forest remnants. Forest fragmentation is an important process contributing to the present-day concerns over biodiversity and rates of extinction. There is now urgent need to identify the key effects of forest fragmentation on biotic systems” (Didham et. al., 1996). Substantial changes in vegetation over a long period of time have caused extensive alterations in the landscape and have led to changes in insect biodiversity. The heterogeneity of an area has been strongly correlated with the number of species in an area and patterns of species diversity are also associated with patterns of spatial and temporal variation. Abundance in biomass and diversity of plant and animal species, ecosystem stability, and variation and diversity of habitats add to species diversity. When the complete clearing of forests continues at the present rate and those ecosystems are replaced with a monoculture of trees or a food crop such as soy beans, the result is a reduction in insect species diversity and abundance (Ananthakrishnan, 2000). Even though specialization of plant feeding insects could not generate diversity by itself, a correlation between resource diversity and species richness with specialization adds the driving force that may lead to diversification of insects (Janz et al., 2006). Over the last decade, much concern has been given to the decline in pollinator insects. The decline in abundance and diversity of pollinators has been caused by different types of anthropogenic disturbances. Deforestation and habitat fragmentation with open, sparse growth within the understory has resulted in significant declines in pollinator flower visitation. Pollinator flower visits were reduced by more than twofold as distances from the flowers to the forest increased. The number of pollinator insects was diminished and a diversity reduction 2 occurred that led to a more homogeneous group of pollinators. Evidence of this was observed as the distance from the flowers to the forests’ edge increased (Chacoff et al., 2006). Hundreds of species of insects and arthropods have the capability of survival on the fragmented remnants free of human habitation (Hendericson, 1930; Evans, 1975; Panzer, 1988; Panzer et al., 2000). However, many arthropod species are incapable of habiting human- dominated landscapes (Panzer et al., 1995; Panzer, 2000). Isolated as small populations on what are essentially small habitat islands, these species are remnant-requiring or “remnant-dependent” organisms (Panzer et al., 1995; 1997; 2000). Landscapes are defined as heterogeneous land areas composed of clusters of interacting ecosystems (Pichcourt et al, 2005). The quality and spatial structure of landscapes since the 1950s have evolved under the influence of human activities to endanger a large number of species. These activities include the alterations by humans, such as poor land use patterns, industrial activity, and agriculture or natural disturbances. Habitat fragmentation is one of the major causes of biodiversity erosion (Pichcourt et al., 2005). The investigation of forest arthropod dynamics is discussed in numerous studies which consider the behavior of populations as a function of the condition of a forest. Insect populations can demonstrate a wide spectrum of patterns, from nearly stationary to oscillating and quasi-chaotic (Bazykin et al., 1995). Studies of watershed nutrient dynamics