UVM Theses and Dissertations
Format:
Print
Author:
Hart, Edmund Melhado
Dept./Program:
Biology
Year:
2011
Degree:
PhD
Abstract:
Climate change is one ofthe most important problems facing ecologists today. While its impacts have become better understood for single species distributions and abundances, less in known about how it will alter dynamic processes at the population and higher level. Using experimental mesocosms based on vernal ponds, I investigated the following aspects of climate change:(i) How will climate change alter the population abundance of invertebrates and can we understand what are the dynamical drivers of those abundance changes? (ii) What will happen to food-web structure as the climate change creates more variable habitat? (iii) Can climate change be an agent of selection and what is the mechanistic basis for th, e selective pressure it exerts? I conducted the following three experiments to answer these questions.
Using aquatic mesocosms I tested how variable precipitation expected with climate change will alter population abundance and dynamics. I found that for Culicidae (mosquitoes), average abundance decreased as mean water levels increased, and for Chironomidae (non-biting midges) had the greatest mean abundance at high mean water levels and low variability. We then fit Gompertz logistic population growth models to time series for our two taxa. We found that the changes in abundance were driven by different parameters. Culicidae tended to have increasing population growth rates with decreasing water levels whereas Chironomidae abundance changed because density dependence decreased in high mean water level and low variability conditions. I demonstrated that climate change can drive abundance patterns but not necessarily through the same mechanism.
Next I used another mesocosm study to examine community dynamics under climate change using two parameters, pond drying rate and rainfall regularity. Here I constructed 81 artificial ponds and applied climate change treatments over three years with weekly samplings of the invertebrate community. Using that data I calculated food web metrics for each weekly sampling for each pond to quantify how climate change might alter web structure. I analyzed the median values of each ponds time series and found that ponds with a lower drying rate (current drying rate) had higher species richness (S), links per species (LIS), longer average chain length (ChnLen), and a high proportion of predatory taxa (P). I also found an increase in temporal variance of ChnLn and P, and a decrease in temporal autocorrelation for LIS in ponds with high drying rates (future climate) implying more unstable food webs with climate change.
Finally using the same system, I raised Daphnia pulex in a common garden experiment from twelve of my most extreme factor combinations. I measured morphological and life history characters three times a week for six weeks. Using Bayesian ANOVA's I found two traits that demonstrated an additive effect of drying rate and rainfall, neonate spine-length and intrinsic growth rate. Both of these are effects that can be predicted from earlier work on Daphnia pulex and predators. In my mesocosms predator abundance was correlated with both of my treatments in a similar additive manner as well as both traits, implying that climate change can act as a selective agent mediated through biotic interactions.
Using aquatic mesocosms I tested how variable precipitation expected with climate change will alter population abundance and dynamics. I found that for Culicidae (mosquitoes), average abundance decreased as mean water levels increased, and for Chironomidae (non-biting midges) had the greatest mean abundance at high mean water levels and low variability. We then fit Gompertz logistic population growth models to time series for our two taxa. We found that the changes in abundance were driven by different parameters. Culicidae tended to have increasing population growth rates with decreasing water levels whereas Chironomidae abundance changed because density dependence decreased in high mean water level and low variability conditions. I demonstrated that climate change can drive abundance patterns but not necessarily through the same mechanism.
Next I used another mesocosm study to examine community dynamics under climate change using two parameters, pond drying rate and rainfall regularity. Here I constructed 81 artificial ponds and applied climate change treatments over three years with weekly samplings of the invertebrate community. Using that data I calculated food web metrics for each weekly sampling for each pond to quantify how climate change might alter web structure. I analyzed the median values of each ponds time series and found that ponds with a lower drying rate (current drying rate) had higher species richness (S), links per species (LIS), longer average chain length (ChnLen), and a high proportion of predatory taxa (P). I also found an increase in temporal variance of ChnLn and P, and a decrease in temporal autocorrelation for LIS in ponds with high drying rates (future climate) implying more unstable food webs with climate change.
Finally using the same system, I raised Daphnia pulex in a common garden experiment from twelve of my most extreme factor combinations. I measured morphological and life history characters three times a week for six weeks. Using Bayesian ANOVA's I found two traits that demonstrated an additive effect of drying rate and rainfall, neonate spine-length and intrinsic growth rate. Both of these are effects that can be predicted from earlier work on Daphnia pulex and predators. In my mesocosms predator abundance was correlated with both of my treatments in a similar additive manner as well as both traits, implying that climate change can act as a selective agent mediated through biotic interactions.