Doctor of Philosophy / Division of Biology / Brett K. Sandercock / Impacts of climate change on biological systems include shifts in seasonal phenology. How do migratory animals adjust reproductive decisions as they shift timing of breeding? I investigated patterns of climate change at a network of Arctic sites in Alaska and Canada, and examined the impacts of climate change on the breeding phenology, reproductive performance, and trophic interactions of Arctic-breeding shorebirds. First, I compared the breeding performance of three species, Western Sandpiper, Semipalmated Sandpiper, and Red-necked Phalaropes, at Nome, Alaska, across a 14-year interval. I found that shorebirds responded to a decreasing temperature during laying by delaying timing of breeding. Delayed breeding shortened the incubation duration for two biparental species but extended incubation for a uniparental species. Despite a short Arctic summer, the breeding windows of three sympatric species were temporally distinct. The three species often nested within several meters from each other, but bred under different temperature regimes and adjusted their reproductive output to different sets of environmental factors. Shifts in breeding phenology can disrupt trophic interactions, especially the phenological match between peak prey availability and hatching of shorebirds. Comparing the extent of phenological mismatch between six shorebirds and their invertebrate prey at ten Arctic sites, peak demand of shorebird broods occurred on average 3.8 days (± 13.8) later than local food peaks, and population demand curves overlapped with food curves by 47% (± 14%). Latitudinal and longitudinal gradients in the extent of trophic mismatch were mediated through geographic variation in the seasonal phenology of invertebrates and shorebirds. For individual nests, both more northerly and easterly sites showed greater phenological mismatch with annual food peaks. Delayed emergence of food peaks at more northerly and easterly sites alleviated the extent of phenological mismatch. My multi-site study provides the first evidence that large-scale geographic processes can determine the extent of phenological mismatch in a bitrophic system. Trends of climate change are sensitive to breeding stages and also vary along a longitudinal gradient. Variability in climatic trends in the Arctic, combined with species-dependent responses to local climate change, indicate that it will be challenging to predict the impacts of future climate change.

Climate change and introduced species are among the top five threats to freshwater systems face. Tropical regions are considered to be especially sensitive to the effects of climate change, while island systems are more susceptible to species introductions. Climate-driven changes in rainfall are predicted to decrease streamflow and increase flash flooding in many tropical streams. In addition, guppies (Poecilia reticulata), an invasive fish, have been introduced to many tropical freshwater ecosystems, either intentionally for mosquito population control, or accidentally because of the aquarium trade. This dissertation examines the effects of climate-driven change in rainfall and introduced guppies on stream structure (resource and invertebrate biomass and composition) and function (nutrient recycling) in Trinidad and Hawaii. In the first data chapter we used a time series to examine how nutrient recycling of guppies changes in the first 6 years after introduction to a new habitat and to examine drivers of these changes. We found that when guppy populations establish in a new environment, they show considerable variation in nutrient recycling through time. This resulted from changes in guppy density in the first two years of introductions, and changes in individual excretion in subsequent stages. In the following chapter we utilized a rainfall gradient that mimics forecasted, climate-driven changes in precipitation and resulting changes in streamflow to examine the effects of climate change on stream food resources and macroinvertebrates. We found that the drying of streams across the gradient was associated with a decrease in resource quality and a 35-fold decline in macroinvertebrate biomass. Invertebrate composition also switched to taxa with faster turnover rates. In the third data chapter we used this same space-for-time substitution approach to determine if climate-driven changes in stream structure also affected stream function. We showed that population nutrient recycling rates declined at the drier end of our rainfall gradient as a result of drops in population densities. We also found that under the current climate scenario, community excretion supplied up to 70% of the nutrient demand, which was ten-fold lower with projected climate changes in streamflow. Lastly, since freshwater ecosystems often face multiple human impacts, including climate change and invasive species, we wanted to understand how climate-driven changes in flow might alter the impact of introduced guppies on stream ecosystems. We selected several streams with guppies and several without guppies along the Hawaii rainfall gradient to examine if the effect of guppies changed with differences in streamflow. We found that the two stressors had synergistic effects on macroinvertebrate biomass and nutrient recycling rates. We concluded that climate change appeared to enhance effects of guppies, through direct and indirect effects. Overall, this dissertation shows that both climate change and species invasion can affect stream ecosystems at multiple levels of organization. This dissertation demonstrates that the effects of anthropogenic stressors are not static through time, and emphasizes the need and utility of using several methodological approaches when measuring the temporal effects of stressors. We also underline the significance of assessing multiple stressor interactions, as more than one stressor often impacts ecosystems. / Graduate / 2019-09-01

Increasingly unpredictable, extreme and erratic rainfall with higher temperatures threatens to undermine the adaptive capacity of food systems and ecological resilience of smallholder landscapes. Despite growing concern, land managers still lack quantitative techniques to collect empirical data about the potential impact of climatic variability and change. This thesis aims to assess how ecosystem services and function and how this links with biodiversity and human wellbeing in smallholder agro-ecosystems in a changing climate. To this end, rather than relying on scenarios or probabilistic modelling, space was used as a proxy for time to compare states in disparate climatic conditions. Furthermore, an integrated methodological framework to assess ecosystem services at the field and landscape level was developed and operationalised, the results of which can be modelled with measures of wellbeing. Various multidisciplinary analytical tools were utilised, including ecological and socio-economic surveys, biological assessments, participatory open enquiry, and documenting ethnobotanical knowledge. The study was located within monsoon rice farms in the Terai Plains of Nepal, and dry season vegetable farms in Northern Ghana. Sites were selected that are climatically and culturally diverse to enable comparative analysis, with application to broad areas of adaptive planning. The linkages that bring about biophysical and human changes are complex and operate through social, political, economic and demographic drivers, making attribution extremely challenging. Nevertheless, it was demonstrated that within hotter and drier conditions in Ghana long-tongued pollinators and granivores, important for decomposition processes and pollination services, are more abundant in farms. Results further indicated that in cooler and drier conditions in Nepal, the taxonomic diversity of indigenous and close relative plant species growing in and around farms, important for the provisioning of ecosystem services, decreases. All other things equal, in both Nepal and Ghana findings indicate that overall human wellbeing may be adversely effected in hotter conditions, with a potentially significantly lower yields, fewer months of the year in which food is available, higher exposure to natural hazards and crop loss, unemployment, and psychological anxiety. Yet, surveys indicate smallholders continue to maintain a fair diversity of species in and around farms, which may allow them to secure basic necessities from provisioning ecosystem services. Moreover, farmers may employ adaptive strategies such as pooling labour and food sharing more frequently, and may have greater access to communication, technology, and infrastructure. Novel methodological and empirical contributions of this research offer predictive insights that could inform innovations in climate-smart agricultural practice and planning.