acase@tulane.edu / 1 / Luke Browne

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Theoretical and empirical work has shown that community diversity and composition can be influenced by both local conditions and dispersal from a regional species pool. This may be especially true shortly after environmental disturbances, because perturbations can provide spatial or temporal niche opportunities for dispersers to establish. Theory predicts that after environmental disturbances tolerant functionally-redundant dispersing species can establish in disturbed communities, maintaining local community diversity and ecosystem function; however, this model relies on the successful establishment of dispersers (i.e., the community must be invasible). Invasibility is expected to decline as time-since-disturbance increases because the local community can use freed resources and increases in abundance. Although studies have acknowledged that timing may influence invasibility, very few studies have focused on how dispersal timing influences the role of dispersal in community response to disturbance. My thesis was conducted to test the role of crustacean zooplankton dispersal timing in the establishment success, and subsequent influence on diversity and ecosystem function of dispersers. To assess this, a field mesocosm study was completed in Churchill, Canada to test the effects of disturbance (nutrients and salinity) and immigration timing (from 51 regional ponds/pools) on invasibility, local community structure and ecosystem functioning (i.e., chl-a). Results show that invasibility was initially high following disturbance, but decreased with time- since-disturbance as the resident community exerted priority effects over dispersers. As a result community diversity was most influenced by immigration when dispersers were added shortly after disturbance. Many coarse measures of diversity were resistant to disturbance, but community composition and the relative abundance of functional groups shifted, and likely influence ecosystem function (i.e., chl-a). When dispersers were added to disturbed communities ecosystem function was recovered to undisturbed levels. Overall, my results suggest that dispersal timing can influence the role of dispersal in communities and the ability of species to capitalize on windows of invasion opportunity will influence their ability to establish in favorable local patches. / Thesis (Master, Biology) -- Queen's University, 2012-09-17 12:18:16.015

Parasites and other associates can play an important role in shaping the communities of their hosts; and their hosts, in turn, shape the community of host-associated organisms. This makes the study of associates vital to understanding the communities of their hosts. Mites associated with bees have a range of lifestyles on their hosts, acting as anything from parasitic disease vectors to harmless scavengers to mutualistic hive cleaners. For instance, in Apis mellifera (the European honey bee) the parasitic mite Varroa destructor has had a dramatic impact as one of the causes of colony-collapse disorder. However, little is known about mites associated with bees outside the genus Apis or about factors influencing the makeup of bee-associated mite communities. In this thesis, I explore the mite community of bees of the genus Bombus and how it is shaped by extrinsic and intrinsic aspects of the bees' environment at the individual bee, bee species, and bee community levels. Bombus were collected from 15 sites in the Ottawa area along a land-use gradient and examined for mites. The number of individual mites and number of mite species hosted by particular bee species increased significantly with bee species abundance. In addition, several bee species differed in terms of mite abundance, mite species richness, mite prevalence, and mite diversity at the level of individual bees and at the species level. In particular, individuals of rare bee species tended to have particularly high mite abundance in comparison to other bees. However, geography, site quality, and bee diversity were never significant predictors of mite community attributes at any level of analysis. Overall, the best predictor of bee-mite community attributes is the bee species themselves. Thus, these mite communities were not shaped by the factors that are known to shape the parasite communities of other species (i.e., geographic distance, host diversity), perhaps because of the commensalistic nature of most of the mite species investigated here. These findings have implications for conservation of bumble bees, given that commensals may become cleptoparasitic at high densities and may act as disease vectors.

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No description available.

In its introduced southern hemisphere range, Sirex noctilio causes considerable mortality in non-native pine forests. In its native Eurasian range however, S. noctilio is of little concern perhaps due to interactions with a well-developed community of pine-inhabiting insects and their associated microorganisms. If such interactions occur, they may limit the woodwasp’s impact in its newly introduced range in North America. My research addresses two broad questions: 1) Does S. noctilio share its habitat with other insects and if so, with whom? 2) Is there evidence that co-habitants affect S. noctilio, and if so how might such interactions occur? Field studies undertaken to describe the woodwasp’s host-attack ecology in Pinus sylvestris showed S. noctilio activity occurred between mid-July and late August, and other phloem- and woodborers sometimes entered the tree after the woodwasp. Tree mortality occurred from two weeks to several months after initial woodwasp symptoms. Suppressed or intermediate trees, those with ≤ 25% residual foliage, or those with stem injury or previous woodwasp symptoms were most likely to have symptoms of woodwasp attack. A second field study conducted to identify associated insect species in S. noctilio-infested Pinus sp. showed the wasp was sometimes found alone, but usually shared the tree with other phloem- or woodboring insects, most commonly the curculionids Tomicus piniperda, Pissodes nemorensis and Ips grandicollis and the cerambycid Monochamus carolinensis. I found no indication that wasps were absent when beetles were present, but there was evidence that woodwasps were less abundant, but larger, when beetles were present. Experiments showed that indirect interactions can occur between the two insect groups via fungal associates of one or both. In the laboratory, the woodwasp symbiont was outcompeted by two beetle-associated fungi, Leptographium wingfieldii and Ophiostoma minus, over a range of temperatures. Under field conditions the woodwasp was able to detect and avoid ovipositing in P. sylvestris inoculated with L. wingfieldii, but its oviposition was unaffected by O. minus. My results show that insects co-habiting pine with S. noctilio have potential to exert a measure of biological control on the woodwasp and may help to limit its impact in North America.

In its introduced southern hemisphere range, Sirex noctilio causes considerable mortality in non-native pine forests. In its native Eurasian range however, S. noctilio is of little concern perhaps due to interactions with a well-developed community of pine-inhabiting insects and their associated microorganisms. If such interactions occur, they may limit the woodwasp’s impact in its newly introduced range in North America. My research addresses two broad questions: 1) Does S. noctilio share its habitat with other insects and if so, with whom? 2) Is there evidence that co-habitants affect S. noctilio, and if so how might such interactions occur? Field studies undertaken to describe the woodwasp’s host-attack ecology in Pinus sylvestris showed S. noctilio activity occurred between mid-July and late August, and other phloem- and woodborers sometimes entered the tree after the woodwasp. Tree mortality occurred from two weeks to several months after initial woodwasp symptoms. Suppressed or intermediate trees, those with ≤ 25% residual foliage, or those with stem injury or previous woodwasp symptoms were most likely to have symptoms of woodwasp attack. A second field study conducted to identify associated insect species in S. noctilio-infested Pinus sp. showed the wasp was sometimes found alone, but usually shared the tree with other phloem- or woodboring insects, most commonly the curculionids Tomicus piniperda, Pissodes nemorensis and Ips grandicollis and the cerambycid Monochamus carolinensis. I found no indication that wasps were absent when beetles were present, but there was evidence that woodwasps were less abundant, but larger, when beetles were present. Experiments showed that indirect interactions can occur between the two insect groups via fungal associates of one or both. In the laboratory, the woodwasp symbiont was outcompeted by two beetle-associated fungi, Leptographium wingfieldii and Ophiostoma minus, over a range of temperatures. Under field conditions the woodwasp was able to detect and avoid ovipositing in P. sylvestris inoculated with L. wingfieldii, but its oviposition was unaffected by O. minus. My results show that insects co-habiting pine with S. noctilio have potential to exert a measure of biological control on the woodwasp and may help to limit its impact in North America.

The distribution and abundance of organisms is influenced by historical, abiotic, and biotic factors. The goal of my dissertation was to determine the distribution of anurans in the Big Bend region of the Chihuahuan Desert and to examine how abiotic and biotic factors shape the composition and structure of anuran communities at multiple spatial scales. My approach relied on extensive field surveys, laboratory and field experiments, and GIS modeling. Results from field surveys and reciprocal transplant studies of tadpoles indicate that abiotic conditions of the breeding site most likely do not play a significant role in causing the segregation of species among individual breeding pools. I used laboratory and mesocosm experiments to test for indirect and direct effects of predators on growth and survival of S. couchii tadpoles. I found that S. couchii tadpoles do not alter their behavior in the presence of predators and are very susceptible to predation. Although tadpoles reared with predators suffered high mortality rates, they metamorphosed significantly faster than tadpoles reared without predators. The reduced time to metamorphose is likely a result of the thinning of intraspecific competitors. Because the primary cause of death for S. couchii tadpoles is desiccation due to pond drying, predators may play an important role in facilitating metamorphosis by decreasing competitors and thus increasing per capita resources, therefore decreasing time to metamorphosis for the surviving tadpoles. At the landscape level anuran distributions seem to be influenced by environmental factors that influence the survival of the adult stage. At the level of the breeding site, microhabitat and abiotic components of the aquatic environment do not seem to play an important role in influencing breeding site use by different species. Rather, it seems likely that predation on tadpoles by predators is important in limiting the distribution of some species and that the fast-developing S. couchii may exclude other species from using sites via oophagy and predation on small tadpoles. My research elucidates the fact that in order to understand factors important in regulating ecological communities it is important to examine both abiotic and biotic factors at multiple spatial scales.