Browsing by Author "Dunham, Amy E"

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    Phenological shifts and species interactions: Disentangling the role of timing and synchrony
    (2014-10-14) Rasmussen, Nicholas; Rudolf, Volker H. W.; Miller, Tom EX; Cox, Dennis D; Dunham, Amy E
    Most habitats exhibit seasonal changes in environmental conditions. These seasonal patterns can vary among years, which can alter the timing of the seasonal life-history events, or phenologies, of species (e.g., emergence from dormancy, migration, reproduction). Species, and individuals within species, oftentimes differ in their phenological responses to year-specific conditions, which could alter the stage at which species interact. We do not have a good understanding of how these shifts in the timing of species interactions affect the outcome of those interactions, but determining the consequences is critical for understanding the dynamics of natural communities. Here, I use a series of experiments with communities of pond-dwelling insects and amphibians to determine how shifts in phenological timing affect intra- and interspecific interactions and whether these effects scale up to alter demographic rates, community structure, and ecosystem functioning. Specifically, I manipulated the mean hatching time (i.e., time of arrival to the habitat) for one species relative to another and/or the amount of variation in arrival time by individuals of a species around a mean date (i.e., degree of synchrony). First, I manipulated differences in mean arrival time for two species that interact as intraguild predators and found that the changes in relative size mediated by shifts in arrival time had strong effects on interactions. Specifically when arrival differences were small, the two species coexisted in similar abundances, but when arrival differences were large, the early arriver excluded the late arriver through predation. Second, I manipulated mean arrival time of one species relative to a predator and a competitor to determine how phenological shifts affected predator-prey and competitive interactions. I found that shifts in the arrival time of a single species within a community can affect the outcome of both interaction types strongly enough to alter community structure, and these changes to community structure scaled up to affect one of three ecosystem-level processes measured. Third, I manipulated variation in the synchrony of arrival, as well as initial density, of a species to determine the consequences for intraspecific competition. I found that variation in synchrony altered several demographic rates of the species, and these effects were density dependent. Finally, I used a factorial manipulation of the mean and synchrony of arrival by a prey species in the presence of a predator to determine how this variation affected predator-prey interactions. I found that the effects of variation in these two aspects of phenology on prey survival were additive, with survival declining with later arrival and lower arrival synchrony. Taken together, these results clearly demonstrate that shifts in phenological timing can have strong effects on intra- and interspecific interactions. These effects of phenological shifts on species interactions frequently scaled up to alter the structure of communities, and were even capable of affecting ecosystem-level processes. This work represents an important and novel contribution to our understanding of the dynamics of seasonal communities and will also be useful in understanding how climate change will alter these dynamics.
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    Reproductive ecology and coexistence among trees in the Guineo-Congolian understory
    (2020-11-30) Drager, Andrea Pilar; Dunham, Amy E
    The exceptional tree biodiversity found in tropical rainforests is possible because many species coexist at low frequencies. While rarity may be an advantage when it comes to growth and survival, it may be a disadvantage in the context of reproductive success. Most tropical trees are adapted for pollination by animals, and populations at low densities and frequencies may be poorer competitors for pollination services and experience reduced reproductive success. Therefore, species that persist at low frequencies may have traits that help them cope with pollination when rare. Additionally, spatiotemporal variation in flowering patterns may alter the relative abundance relationships among species in ways that influence plant-pollinator interactions. We ask how biotic interactions, abiotic drivers and reproductive traits might interact to influence the reproductive success and persistence of cooccurring species. We answer this using spatially-explicit observational data from a guild of understory trees in Korup National Park, Cameroon, during the 2016 peak flowering season. In Chapter 1, we find that individual flowering probability is positively related to tree size and decreases with local species abundance, thus decreasing the relative abundance extremes among rare and common species during reproduction. It is not structured by shared ancestry and is unrelated to degree of neighborhood crowding or habitat differences. In Chapter 2, we find that the plant-pollinator interactions in this previously unstudied community are broadly ecologically generalized but that floral scent is a key trait involved in resource partitioning among insect groups, particularly among Diptera and Hymenoptera. In Chapter 3, we focus on the speciose Cola genus, and find that despite both morphologically generalized flowers and high pollination niche overlap, visitation rates are not sensitive to local or plot level flowering frequencies or floral display size and are uncorrelated with pollination success. Higher pollen limitation in abundant species compared to rarer species may be due to reproductive traits that promote outcross pollination. Together, these findings highlight the importance of understanding species reproductive dynamics from a community perspective and show that species trait differences may be key to understanding how pollination contributes to the persistence of rare species, and to biodiversity maintenance more broadly.
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    The Fieldwork Wellness Framework: a new approach to field research in ecology
    (Wiley, 2023) Nordseth, Anna E; Gerson, Jacqueline R; Aguilar, Lucrecia K; Dunham, Amy E; Gentles, Anecia; Neale, Zoey; Rebol, Erynn
    Fieldwork is often an important aspect of research in ecology, evolution, and conservation biology (EECB), but individuals of marginalized identities are likely to experience compromised wellness. The responsibility for structurally changing fieldwork to improve experiences and outcomes falls on the entire EECB community. We propose a Fieldwork Wellness Framework to replace traditional fieldwork approaches, which are hazardous and ill-suited to today's increasingly diverse EECB community and its goals. The purpose of this Framework is to prevent and manage risk while also promoting holistic well-being for all field research participants. We outline nine facets of the Framework: acknowledge and address identity, create a code of conduct, promote and practice self-care, form local connections, use support structures in decision making, host and attend trainings, address financial concerns, enact emergency plans, and debrief. By centering wellness in the planning and performing of fieldwork, EECB can cultivate a more diverse, equitable, inclusive, healthy, and productive community.