Showing papers by "Daniel M. Tompkins published in 2013"

The Trojan female technique: a novel, effective and humane approach for pest population control

Abstract: Humankind's ongoing battle with pest species spans millennia. Pests cause or carry disease, damage or consume food crops and other resources, and drive global environmental change. Conventional approaches to pest management usually involve lethal control, but such approaches are costly, of varying efficiency and often have ethical issues. Thus, pest management via control of reproductive output is increasingly considered an optimal solution. One of the most successful such ‘fertility control’ strategies developed to date is the sterile male technique (SMT), in which large numbers of sterile males are released into a population each generation. However, this approach is time-consuming, labour-intensive and costly. We use mathematical models to test a new twist on the SMT, using maternally inherited mitochondrial (mtDNA) mutations that affect male, but not female reproductive fitness. ‘Trojan females’ carrying such mutations, and their female descendants, produce ‘sterile-male’-equivalents under natural conditions over multiple generations. We find that the Trojan female technique (TFT) has the potential to be a novel humane approach for pest control. Single large releases and relatively few small repeat releases of Trojan females both provided effective and persistent control within relatively few generations. Although greatest efficacy was predicted for high-turnover species, the additive nature of multiple releases made the TFT applicable to the full range of life histories modelled. The extensive conservation of mtDNA among eukaryotes suggests this approach could have broad utility for pest control.

Predicted responses of invasive mammal communities to climate-related changes in mast frequency in forest ecosystems.

Abstract: Predicting the dynamics and impacts of multiple invasive species can be complex because ecological relationships, which occur among several trophic levels, are often incompletely understood. Further, the complexity of these trophic relationships exacerbates our inability to predict climate change effects on invaded ecosystems. We explore the hypothesis that interactions between two global change drivers, invasive vertebrates and climate change, will potentially make matters worse for native biodiversity. In New Zealand beech (Nothofagus spp.) forests, a highly irruptive invasive mammal community is driven by multi-annual resource pulses of beech seed (masting). Because mast frequency is predicted to increase with climate change, we use this as a model system to explore the extent to which such effects may influence invasive vertebrate communities, and the implications of such interactions for native biodiversity and its management. We build on an established model of trophic interactions in the system, combining it with a logistic probability mast function, the parameters of which were altered to simulate either contemporary conditions or conditions of more or less frequent masting. The model predicts that increased mast frequency will lead to populations of a top predator (the stoat) and a mesopredator (the ship rat) becoming less irruptive and being maintained at appreciably higher average abundances in this forest type. In addition, the ability of both current and in-development management approaches to suppress invasive mammals is predicted to be compromised. Because invasive mammals are key drivers of native fauna extinction in New Zealand, with the additional loss of associated functions such as pollination and seed dispersal, these predictions imply potentially serious adverse impacts of climate change for the conservation of biodiversity and ecosystem function. Our study also highlights the importance of long-term monitoring data for assessing and managing future impacts of global change drivers.

Native fish avoid parasite spillback from multiple exotic hosts: consequences of host density and parasite competency

Abstract: Disease-mediated impacts of exotic species on their native counterparts are often ignored when parasite-free individuals are translocated. However, native parasites are frequently acquired by exotic species, thus providing a mechanism through which native host-parasite dynamics may be altered. In Argentina, multiple exotic salmonids are host to the native fish acanthocephalan parasite Acanthocephalus tumescens. Field evidence suggests that rainbow trout, Oncorhynchus mykiss, may be a major contributor to the native parasite’s population. We used a combination of experimental infections (cystacanth—juvenile worm transmission from amphipod to fish; post-cyclic—adult worm transmission between definitive fish hosts) and dynamic population modelling to determine the extent to which exotic salmonid hosts may alter A. tumescens infections in native freshwater fish. Experimental cystacanth infections demonstrated that although A. tumescens establishes equally well in native and exotic hosts, parasite growth and maturity is superior in exotic O. mykiss. Experimental post-cyclic infections also showed greater establishment success of A. tumescens in O. mykiss, though post-cyclic transmission did not result in greater parasite size or maturity. Dynamic population modelling, however, suggested that exotic salmonids may have a very limited influence on the A. tumescens population overall, due to the majority of A. tumescens individuals being maintained by more abundant native hosts. This research highlights the importance of considering both a host’s relative density and its competency for parasites when evaluating whether exotic species can modify native host-parasite dynamics.

Local effects of a global problem: modelling the risk of parasite-induced mortality in an intertidal trematode–amphipod system

Abstract: The interactive effects of climate change and parasitism are of concern because of potentially important consequences for host populations, communities and entire ecosystems. In marine environments, the absence of historic baseline data on parasitism and disease limits our ability to make realistic predictions about these consequences. Here, we adapt a simulation model developed for a Northern Hemisphere intertidal host–parasite system to a comparable system in the Southern Hemisphere. The entire life cycle of the intertidal trematode parasite Maritrema novaezealandensis was modelled in order to investigate the interactive effects of parasitic infections and increasing temperatures on the population dynamics of the amphipod host Paracalliope novizealandiae. Despite uncertainties associated with the model and its parameterisation, most temperature increases that were predicted to cause the collapse of the modelled amphipod population in the long term lay within the range of predicted warming for the study area. The high vulnerability of the amphipods in the modelled system illustrates a potentially important ecological mechanism by which consequences of a global problem might manifest on the local scale.

Relative competence of native and exotic fish hosts for two generalist native trematodes

Abstract: Exotic fish species frequently acquire native parasites despite the absence of closely related native hosts. They thus have the potential to affect native counterparts by altering native host–parasite dynamics. In New Zealand, exotic brown trout Salmo trutta and rainbow trout Oncorhynchus mykiss have acquired two native trematodes (Telogaster opisthorchis and Stegodexamene anguillae) from their native definitive host (the longfin eel Anguilla dieffenbachii). We used a combination of field surveys and experimental infections to determine the relative competence of native and exotic fish hosts for these native parasites. Field observations indicated that the longfin eel was the superior host for both parasites, although differences between native and exotic hosts were less apparent for S. anguillae. Experimental infections indicated that both parasites had poorer establishment and survival in salmonids, although some worms matured and attained similar sizes to those in eels before dying. Overall, the field surveys and experimental infections indicate that these exotic salmonids are poor hosts of both native trematodes and their presence may decrease native parasite flow to native hosts.

Surveillance for arboviral zoonoses in New Zealand birds.

Abstract: Introduction Given the significant burden that emerging infectious diseases place on global economies and public health, the monitoring and mitigation of, and early response to, potential infectious diseases are of the highest priority. The objective of this study was to survey for known and other potential arboviral zoonoses in multiple bird species at four locations in New Zealand. Methods Common bird species were targeted for blood sampling during two southern hemisphere summers. Sera from each period (n = 185 and n = 693) were screened in an epitope blocking enzyme immunoassay for flavivirus antibody detection. In the first season, testing for antibodies to specific alphaviruses was conducted on samples with sufficient sera (n = 22). In the second season, blood clots (n = 544) were screened for viral presence by polymerase chain reaction (PCR) for alphaviral and flaviviral RNA, and virus isolation (n = 146) was conducted. Results Flavivirus antibodies were detected in 13 species, and one Australasian gannet (Morus serrator) from one site was positive for antibodies to Ross River virus. PCR tests and virus isolation were all negative. Discussion Evidence for flavivirus exposure in seabirds at Kaikoura Peninsula and Cape Kidnappers suggests that viruses isolated from seabirds and associated ticks in New Zealand in the late 1970s are still present. Evidence for flavivirus exposure in passerines at Kaikoura Peninsula, Cape Kidnappers and Mokoia Island is novel. The Ross River virus finding is also new and supports the hypothesis that migratory seabirds are an import pathway for such agents into New Zealand.