Browsing by Author "Rudolf, Volker"

Now showing 1 - 4 of 4
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    Experimental evidence that local interactions select against selfish behaviour
    (Wiley, 2021) Boots, Mike; Childs, Dylan; Crossmore, Jessica; Tidbury, Hannah; Rudolf, Volker
    How social behaviours evolve remains one of the most debated questions in evolutionary biology. An important theoretical prediction is that when organisms interact locally due to limited dispersal or strong social ties, the population structure that emerges may favour cooperation over antagonism. We carry out an experimental test of this theory by directly manipulating population spatial structure in an insect laboratory model system and measuring the impact on the evolution of the extreme selfish behaviour of cannibalism. We show that, as predicted by the theory, Indian meal moth larvae that evolved in environments with more limited dispersal are selected for lower rates of cannibalism. This is important because it demonstrates that local interactions select against selfish behaviour. Therefore, the ubiquitous variation in population structure that we see in nature is a simple mechanism that can help to explain the variation in selfish and cooperative behaviours that we see in nature.
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    Multiple invasions: invader interactions and multiple anthropogenic factors in wetland communities
    (2015-10-22) Meza-Lopez, Maria Magdalena; Siemann, Evan; Rudolf, Volker; Li, Qilin; Armitage, Anna
    Ecosystems invaded by one invader often contain abundant populations of other invaders. This may reflect facilitative invader interactions, common response to anthropogenic factors (nutrient enrichment and/or climate warming), or result from common paths of introduction. My dissertation asked 1) do multitrophic invaders reciprocally facilitate each other’s invasion, 2) does nutrient enrichment or climate warming contribute to plant invasions in native plant wetland communities and/or in exotic herbivore invaded communities, and 3) do nutrient enrichment, warming, and plant invasions individually or interactively affect exotic herbivore invasions in native plant communities. Results from a factorial field mesocosm experiment manipulating the order of exotic plant and herbivore invasions showed no evidence of reciprocal invader facilitation that would lead to an invasional meltdown in wetlands invaded by Pomacea maculata and Alternanthera philoxeroides. Pomacea maculata facilitated A. philoxeroides by preferentially consuming native plants. Alternanthera philoxeroides did not facilitate P. maculata invasions, suggesting that P. maculata invasions are independent of A. philoxeroides invasions. A factorial greenhouse mesocosm experiments showed that increasing nutrients directly increase P. maculata size, that exotic plants are not an ideal food source for P. maculata. Another greenhouse study showed that P. maculata size increased with increasing nutrients independent of plant origin (native vs. exotic). I conducted a field mesocosm experiments that showed that nutrient enrichment contributed to plant invasions independent of warming and that warming tended to reduce exotic plant performance. In another field factorial mesocosm experiment, I found that increasing nutrients increased plant growth, but favored exotic plants and that warming increased P. maculata’s reproductive performance four-fold. Together these results suggest that exotic herbivores with great impacts on native plants will facilitate plant invasions, that nutrient enrichment and warming will increase herbivore invasions, and that nutrient enrichment will increase plant invasions. Furthermore, it is critical to assess species interactions and interactive anthropogenic factor effects on native and exotic species because they cannot be predicted based on single anthropogenic factors.
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    Temperature-dependent predator-prey dynamics: unveiling complexities across species and contexts in a warming world
    (2023-11-01) Neale, Zoey R; Rudolf, Volker
    Rising global temperatures have profound influences on natural ecosystems. Direct effects of environmental warming on individual metabolic rates scale up to influence every level of biological organization. Past studies examine direct effects of temperature on individual and population performances, but less attention has been paid to indirect effects on species interactions such as predation. In this thesis I investigate how predator thermal responses differ across species and contexts and the implications this can have on prey communities. In my first chapter, I experimentally tested and compared thermal responses of feeding rates of six predators collected from the same habitat to determine how species experiencing similar climatic conditions can vary in respond to temperature changes. I found large disparities in the thermal responses across species. Notably, the differences were large enough to shift the hierarchy of predators feeding on a shared prey along a temperature gradient. In my second chapter I examined whether local historic climate regimes influence thermal responses of species by experimentally comparing thermal responses of predators of the same species collected at different sites spanning a latitudinal gradient of 11°C. I found that thermal responses of populations can differ substantially across latitudes. Predators at higher latitudes demonstrated stronger sensitivities to temperature than predators collected from the lowest latitude. Moreover, differences in the shape of the response curves resulted in range-specific warming effects, with higher latitude predators increasing more than lower latitude predators along one portion of the gradient but decreasing more than lower latitudes along another portion. In my third chapter I explored how thermal responses of intraspecific demographic rates, predation, and interspecific competition among prey interact to influence population dynamics in a three-species food web. I found warming had opposing effects on prey population sizes independent of interspecific interactions, increasing population sizes at colder temperatures but suppressing them at warmer temperatures. Additionally, top-down control was dependent on temperature, with predators suppressing prey population sizes at intermediate-warm temperatures but not cold. Overall, these results highlight the context-dependence of predator-prey interactions to temperature and the need to consider these contexts when predicting and mitigating the effects of climate change.
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    The Antarctic Peninsula's Response to Holocene Climate Variability: Controls on Glacial Stability and Implications for Future Change
    (2015-12-02) Minzoni, Becky Lynn; Anderson, John B; Droxler, André; Nittrouer, Jeffrey A; Rudolf, Volker
    The Antarctic Peninsula is one of the most rapidly changing regions in the Cryosphere, with 87% of its glaciers receding and several ice shelves catastrophically collapsing since observations began in the 1960’s. These substantial, well-documented changes in the ice landscape have caused concern for the mass balance of the Antarctic Peninsula Ice Cap. To better understand the significance of these recent changes, I have assimilated a massive database of new and published marine sedimentary records spanning the Holocene Epoch (the last 11.5 kyrs). The database includes 9 coastal embayments with expanded sedimentary packages and well-dated cores. Each site represents an end-member in the wide range of Antarctic Peninsula oceanography, orography, meteorology, and glacial drainage basin characteristics. Multi-proxy analysis, including sedimentology, geochemistry, and micropaleontology, was conducted at each site to reconstruct glacial history at centennial-scale resolution on par with ice-core data. The coastal sites were then compared in the context published ice-core paleoclimate, paleoceanographic, and glaciological records. The first of these sites, Herbert-Croft Fjord, provides an unparalleled opportunity to compare the marine sediment record with a related ice-core in an Antarctic maritime setting. Herbert-Croft Fjord is the southernmost embayment studied on the eastern side of the Antarctic Peninsula and represents an end-member with a cold, dry atmosphere and cold, saline ocean mass. The record from Herbert-Croft Fjord indicates grounded ice receded quickly and early in the Holocene, followed by a floating ice phase that collapsed 10 ± 2.4 calendar kyrs before present (cal kyr BP, where present day is 1950 A.D.) and never re-advanced. The fjord remained open and productive during the prolonged warm intervals of the Mid Holocene, and began to experience greater glacial influence and sea ice cover during Late Holocene cooling, a period termed the Neoglacial. The second site, Ferrero Bay of the Amundsen Sea, is the southernmost end-member on the western side of the Antarctic Peninsula and represents a truly polar coastal setting. Grounded ice receded from the deep basin much earlier than expected, ~10.7 cal kyr BP, due to warm deep water masses that under-melted the extended ice sheet during the Early Holocene. Ferrero Bay was then covered by the extensive Cosgrove Ice Shelf, which remained stable during the Mid Holocene Hypsithermal and did not recede to its current position until ~2.0 cal kyr BP, coincident with Neoglacial cooling. Thus, Ferrero Bay and the Cosgrove Ice Shelf were starkly out of phase with the northern peninsula sites and apparently were not sensitive to Holocene climate variability but rather to impinging warm ocean currents, which are observed in Ferrero Bay today. Comparison of 9 coastal sites, including Herbert-Croft Fjord, Ferrero Bay, and several other embayments of various local settings, shows highly variable glacial response to Early Holocene warming, with difference in response onset of ± 4.2 kyrs and difference in duration of ± 2.5 kyrs. The Mid Holocene was less variable, with the onset of moderately cooler conditions varying by ± 1.7 kyrs and difference in duration of this epidosde of ± 1.9 kyrs. The Late Holocene Neoglacial by contrast was synchronous with difference in onset and duration of ± 0.7 kyrs and ± 0.7 kyrs, respectively. Later historic events of shorter duration, such as the Little Ice Age, were more synchronous with differences in onset and duration of ± 0.3 kyrs and ± 0.2 kyrs, respectively. Regional glacial behavior became more synchronous during the Holocene as the glaciers and their drainage basins became progressively smaller, rendering them more sensitive to climate change and less influenced by various local forcings such as ocean temperature, basin bathymetry, and precipitation differences. The increase in glacier sensitivity helps explain the current widespread glacial recession in response to the rapid regional warming of ~3.5° C over the last century.