Browsing by Author "Whitney, Kenneth D."
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Item Anoplolepis gracilipes invasion of the Samoan Archipelago: Can mutualisms with native species amplify ecological consequences?(2011) Savage, Amy Marie; Rudgers, Jennifer A.; Whitney, Kenneth D.Integrating mutualism into the study of ecological communities is likely to be critical to understanding community dynamics and to predict the consequences of anthropogenic changes to ecosystems. Invasive species are among the greatest of these threats to global biodiversity. Throughout the Pacific, the invasive ant Anoplolepis gracilipes associates mutualistically with Morinda citrifolia , a native plant with extrafloral nectaries (EFN). I tested the hypothesis that these interactions can mediate invader impacts Anoplolepis gracilipes abundances were positively correlated with the dominance of EFN-bearing plants per site and negatively correlated with the species richness of native ants. Additionally, A. gracilipes displayed a higher magnitude of responses to nectar than other dominant ants. Mutualisms also had significant impacts on the structure of arthropod communities. These effects were strongest when A. gracilipes dominated local ant assemblages. These results suggest that novel mutualisms between invasive and native species can facilitate the impacts of invasions on communities.Item Does phylogeny matter? Assessing the impact of phylogenetic information in ecological meta-analysis(Blackwell Publishing Ltd/CNRS, 2012) Chamberlain, Scott A.; Hovick, Stephen M.; Dibble, Christopher J.; Rasmussen, Nick L.; Van Allen, Benjamin G.; Maitner, Brian S.; Ahern, Jeffrey R.; Bell-Dereske, Lukas P.; Roy, Christopher L.; Meza-Lopez, Maria; Carrillo, Juli; Siemann, Evan; Lajeunesse, Marc J.; Whitney, Kenneth D.Item Evolutionary responses to global change: an experimental test of the effect of altered precipitation on hybridization rates in sunflower (Helianthus)(2013-07-24) Sneck, Michelle; Whitney, Kenneth D.; Miller, Thomas E.; Rudolf, Volker H. W.Climate change is rapidly altering natural ecosystems. Plastic and adaptive responses to climate change (i.e., range shifts and phenology) have been widely noted across taxa. However, the effects of climate change on evolutionary processes such as interspecific gene flow (hybridization) are less well known. In this study, we quantified hybridization rates in response to experimental manipulations of rainfall, an important dimension of global change. We used rain-out shelters in the field and quantified rates of hybridization between two congeners, Helianthus annuus (common sunflower) and H. petiolaris (prairie sunflower). We found that H. annuus maternal plants produced hybrid progeny more than H. petiolaris maternal plants, with a trend for decreased rates of hybridization with increased soil moisture (when rain-out shelters were absent). The relative number of open inflorescences of each species predicted hybridization rates. Thus, this study demonstrates how changing environmental conditions, specifically precipitation, could influence hybridization rates.Item Experimental test of the effects of supportive breeding on wild populations(2008) Hardin, Autumn Nicole; Whitney, Kenneth D.Supportive breeding is currently being used in the management of threatened populations, but the effects of this management strategy remain relatively untested. The common house fly, Musca domestica, was used as a model to assess the relative effectiveness of supportive breeding strategies for endangered species management. Captive populations were subjected to one of two captive breeding treatments, and served as the source of migrants for "wild" populations, which received either 5% or 50% of their total census size from captive migrants each generation. One "wild" population treatment served as a control and received no migrants. Measures of fitness were assessed from each population for nine generations. Within the captive populations, analyses found highly significant declines in fitness across generations, with much higher total fitness in the equalized breeding strategy as compared to the structured breeding scheme. Captive population fitness did not prove to be a good predictor of "wild" population fitness after reintroduction, but the inbreeding co-efficient of the captive populations were found to be correlated with recipient "wild" population fitness. This suggests that captive breeding programs with goals of future reintroduction to the wild should focus on overall kinship as opposed to fitness levels and make every attempt to minimize the co-efficient of inbreeding within the captive population. "Wild" populations that received low levels of ideally bred captive migrants performed significantly better than control populations, which received no outside migration. No other "wild" population treatments were found to differ significantly from the control populations, which may be due in part to the small population sizes that limited the effects of selection and migration and strengthened the influence of factors such as genetic drift and inbreeding. It is likely that the constraints of small population size led to the control populations having the lowest overall fitness. Based on this study, it does not appear that sweeping generalizations can be made about the effects of migrant breeding treatment and level of migration on wild populations. Further research is warranted before supportive breeding programs are implemented for a broader range of threatened and endangered species.Item Habitat use and resource tracking by African Ceratogymna hornbills: implications for seed dispersal and forest conservation(Blackwell Publishing, 1998) Smith, Thomas B.; Whitney, Kenneth D.Conservation of tropical forests requires an understanding of the seasonal patterns of abundance and distribution of important seed dispersers. In the forests of Central Africa, three species of hornbills in the genus Ceratogymna (Aves: Bucerotidae) provide dispersal for over 50 species of trees and lianas, yet their ecology is poorly known. We present the first empirical evidence for resource tracking and large-scale movements by two of these species, which were previously considered resident. Hornbill numbers and fruit production were estimated over a one-year period in the Dja Reserve, Cameroon. Monthly abundances of C. atrata and C. cylindricus varied four- and 12-fold, respectively, and were predicted by community fruit availability as measured by fruitfall on a 4·3 km trail. In contrast, C. fistulator abundances varied little and were not related to fruit availability. Synchronous population fluctuations in sites 22 km distant were observed for atrata and cylindricus, but not for fistulator. Together, these results indicate that atrata and cylindricus populations track fruit resources via seasonal emigrations, while the fistulator population appears to be relatively sedentary. Comparisons of hornbill densities in primary and secondary forests suggest that they are important dispersers in both habitats, and will likely play larger roles in central African forest regeneration as more vulnerable seed dispersers are removed by hunting. If large seasonal movements of hornbills turn out to be a general phenomenon, effective management of central African forest reserves will require greater emphasis on reserve connectivity and on seasonal and spatial patterns of fruit production.Item Seed dispersal by Ceratogymna hornbills in the Dja Reserve, Cameroon(Cambridge University Press, 1998-05) Smith, Thomas B.; Parker, V. Thomas; Hardesty, Britta Denise; Stauffer, Donald J.; Holbrook, Kimberly M.; Lamperti, Aaron M.; Fogiel, Mark K.; Whitney, Kenneth D.Seed dispersal is a process critical to the maintenance of tropical forests, yet little is known about the interactions of most dispersers with their communities. In the Dja Reserve, Cameroon, seed dispersal by the hornbills Ceratogymna atrata, C. cylindricus and C. fistulator (Aves: Bucerotidae) was evaluated with respect to the taxonomic breadth of plants dispersed, location of seed deposition and effects on seed germination. Collectively, the three hornbill species consumed fruits from 59 tree and liana species, and likely provided dispersal for 56 of them. Hornbill-dispersed tree species composed 22% of the known tree flora of the site. Hornbill visit lengths, visit frequencies, and seed passage times indicated that few seeds were deposited beneath parent trees; in five hornbill/tree species pairings studied, 69–100% of the seeds ingested were deposited away from the parent trees. Germination trials showed that hornbill gut passage is gentle on seeds. Of 24 tree species tested, 23 germinated after passage by hornbills; of 17 planted with controls taken directly from trees, only four species showed evidence of inhibition of germination rate, while seven experienced unchanged germination rates and six experienced enhanced germination rates. Results suggested that Ceratogymna hornbills rank among the most important seed dispersers found in Afrotropical forests, and they deserve increased conservation attention. Ceratogymna hornbills are likely to become increasingly important in forest regeneration as populations of larger mammalian seed dispersers (such as forest elephants and primates) diminish.Item Supplementary material to Whitney, K. D., B. Boussau, E. J. Baack, and T. Garland Jr. in press. Drift and genome complexity revisited. PLoS Genetics(2011) Whitney, Kenneth D.; Boussau, Bastien; Baack, Eric J.; Garland, Theodore Jr.; GeneticsItem The Evolutionary Ecology of Stereoisomeric Sesquiterpene Lactones in Xanthium strumarium(2012-11-30) Ahern, Jeffrey; Whitney, Kenneth D.; Rudgers, Jennifer A.; Parry, Ronald J.; Siemann, EvanThe ecological factors that maintain defensive chemical variation within and between plant species have intrigued ecologists for decades. While theory posits that polymorphisms may be maintained different forms of balancing selection, relatively few expeItem VARIATION IN SPECIES INTERACTIONS AND THEIR EVOLUTIONARY CONSEQUENCES(2013-05-13) Chamberlain, Scott A.; Whitney, Kenneth D.; Rudgers, Jennifer A.; Cox, Dennis D.; Rudolf, Volker H. W.Species interactions restrict or promote population growth, structure communities, and contribute to evolution of diverse taxa. I seek to understand how multiple species interactions are maintained, how human altered species interactions influence evolution, and explore factors that contribute to variation in species interactions. In Chapter 1, I examine how plants interact with multiple guilds of mutualists, many of which are costly interactions. The evolution of traits used to attract different mutualist guilds may be constrained due to ecological or genetic mechanisms. I asked if two sets of plant traits that mediate interactions with two guilds of mutualists, pollinators and ant bodyguards, were positively or negatively correlated across 36 species of Gossypium (cotton). Traits to attract pollinators were positively correlated with traits to attract ant bodyguards. Rather than interaction with one mutualist guild limiting interactions with another mutualist guild, traits have evolved to increase attraction of multiple mutualist guilds simultaneously. In Chapters 2 and 3, motivated by the fact that agriculture covers nearly 50% of the global vegetated land surface, I explore the consequences of changes in plant mutualist and antagonist guilds in agriculture for selection on plant traits. I first explore how agriculture alters abundance and community structure of mutualist pollinators and antagonist seed predators of wild Helianthus annuus texanus. Mutualists were more abundant near crops, whereas antagonists were more abundant far from crops near natural habitat. In addition, mutualist pollinator communities were more diverse near sunflower crops. Plant mutualists and antagonists respond differently to agriculture. Next, I explore how these changes in abundance and community structure of mutualists and antagonists influenced natural selection on H. a. texanus floral traits. Natural selection on heritable floral traits differed near versus far from crop sunflowers, and overall selection was more heterogeneous near crop sunflowers. Furthermore, mutualist pollinators and antagonist seed predators mediated these differences in selection. Finally, in Chapter 4, I ask if variation in interaction outcomes differs across types of species interactions. Furthermore, I examined the relative importance of factors that create context-dependency in species interactions. Using meta-analysis of 353 papers, we found that mutualisms were more likely to change sign of the interaction outcome when compared across contexts than competition, and predation was the least likely to change sign. Overall, species identity caused the greatest variation in interaction outcomes: whom you interact with is more important for context-dependency than where or when the interaction occurs. Additionally, the most important factors driving context-dependency differed significantly among species interaction types. Altogether, my work makes progress in understanding how species maintain interactions with multiple guilds of mutualists, how agriculture alters species interactions and subsequent natural selection, and the variation in species interaction outcomes and their causes.