Graduation Year

2011

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Biology (Integrative Biology)

Major Professor

Jason R. Rohr

Keywords

Arthropods, Competition, Insecticides, Phylogeny, Sundews

Abstract

As discussed in Chapter 1, although our understanding of the ecology and evolution of carnivorous plants has greatly improved in recent years, many fundamental questions remain unanswered. Unfortunately, at the present time, many carnivorous plants are increasingly threatened by anthropogenic activities. Indeed, over half of the carnivorous plant species assessed by the International Union for the Conservation of Nature (IUCN) are listed as `threatened', but the threats to carnivorous plants have not previously been quantified. In Chapter 2, I quantified the conservation threats to carnivorous plant taxa worldwide by searching peer-reviewed literature, and found data on the threats to 48 species of carnivorous plants from nine genera. The most common threat was habitat loss from agriculture, followed by the collection of wild plants, pollution, and natural systems modifications. As I found in Chapter 2, while agrochemical pollution is thought to be an important conservation threat to carnivorous plants, the effects of insecticides in particular on these taxa have not previously been quantified. Therefore in Chapter 3 I tested the effects of commercial and technical grades of three widely used insecticides (carbaryl, lambda-cyhalothrin, and malathion) on survival and the expression of traits associated with carnivory of pink sundews (Drosera capillaris) and Venus flytraps (Dionaea muscipula) using a combination of lab- and field-based experiments. Commercial grades were generally more harmful than technical grades under lab and field conditions, but all three insecticides were capable of causing negative effects on the plants within recommended application rates. Pink sundews appeared to be more susceptible to insecticides than Venus flytraps, perhaps because of larger numbers of digestive glands on the leaf surfaces. Given the effects observed, I suggest that the use of insecticides should be carefully managed in areas containing vulnerable carnivorous plant species. For Chapters 4 and 5, I explored the ecological role of carnivorous plants, specifically if they could compete with animals for shared prey resources. In Chapter 4 I characterized the ground-surface spider and arthropod assemblages of two mesic flatwood habitats in Florida, to resolve what the most likely animal competitor was for pink sundews. I identified 31 spider species from 27 genera in 12 families, with wolf spiders (Lycosidae) being the dominant spider family at both sites. Based on their abundance and the behavioral traits they exhibited, I determined that the funnel-web-building wolf spider Sosippus floridanus was the most likely potential competitor with pink sundews. Collembola and Formicidae were the most abundant arthropod taxa present, but ground-surface spiders were not strongly associated with any typical prey groups, suggesting that environmental factors might also be important in structuring this community. Subsequently, in Chapter 5 I examined the potential for competition between carnivorous plants and animals by studying dietary and microhabitat overlap between pink sundews and wolf spiders in the field, and by conducting a lab experiment examining the effects of wolf spiders on sundew fitness. In the field, I found that sundews and spiders had high dietary overlap with each other and with the available arthropod prey. Associations between sundews and spiders depended on spatial-scale: sundews and spiders were both found more frequently in quadrats with more abundant prey, but within quadrats spiders constructed larger webs and located them further away from sundews as the total sundew trapping area increased. Spiders also constructed larger webs when fewer prey were available. In the lab, my experiment revealed that spiders can significantly reduce sundew fitness. All of these results suggest that members of the plant and animal kingdoms can and do compete. These findings provided inspiration for Chapter 6, where I explored if phylogenetic distance was a good predictor of the strength of competition between taxa, using a meta-analytical approach. I collected data from studies published from 1998-2008 in eight ecology journals using the keyword `interspecific competition', gathering a total of 191 effect sizes. I found no significant relationship between phylogenetic distance and the strength of competition, contrary to the long-standing assumption that it should be greatest in strength between closely related species. However, these findings could presently be limited by publication bias, and I suggest several directions for future research.

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