Discontinuities: Predicting the Architecture of Invasions and Extinctions - Aaron Lotz

• Dissertation Defense
• 7/1/2011

One of the major unresolved problems, at the forefront of worldwide environmental concerns, is the increase in non-indigenous species (NIS) and endangered species. Invasions and extinctions fundamentally change community structure, which potentially affects ecosystem processes. This potential loss of ecological processes inherently affects landscape structure and dynamics, including predator-prey interactions, dispersal, foraging behavior and functional group composition.

I explored multiple tenets of the textural discontinuity hypothesis. This hypothesis states that hierarchical landscape structures with scale-specific pattern entrain attributes of animals inhabiting the landscape. Landscapes form hierarchies that are structured by vegetative, geomorphological and contagious disturbance processes. The spatial and temporal patterns inherent in landscapes reflect numerous processes, interacting on distinct scales, which shape the assembly of animal communities. Analysis of body mass patterns and functional group distributions has been suggested as methods to provide insight about these underlying hierarchical processes. Scientists have posited that species at the edges of body mass aggregations may be exposed to highly variable resources. Literature indicates NIS and endangered bird and mammal species occur at the edges of body mass aggregations more frequently than expected. This work focuses on the distribution of biological diversity in space and time and socio-ecological factors that are contributing to the worldwide increase in NIS and endangered species.

I analyzed invasions and extinctions of birds and mammals across five Mediterranean-climate ecosystems and in 100 countries using Bayesian CART analysis and an information-theoretic approach. All body mass distribution data analyzed were discontinuous. This work provided further support for Holling's textural discontinuity hypothesis. Alpha and beta diversity of function decreased in most datasets when NIS were introduced into the community. After the introduction of NIS, I observed a decrease in cross-scale redundancy of functional groups in mammals and when both taxonomic groups were combined. In Eocene Epoch mammal data, speciation events were not detected near body mass aggregation edges. However, this was most likely due to the low power of the statistical tests, high species turnover, and small sample size. Only 64% of the biomes in mammals had ecoregions with similar structure and only 50% of the biomes in birds had ecoregions with similar structure, which may be a result of coarse landscape classification schemes. GDP per capita was positively correlated with the proportion of NIS bird and mammal species within a country. Resilience of a country was correlated to life expectancy. As life expectancy increased, resilience of a country decreased. Results may help us make proper management decisions in monitoring particular non-indigenous species and focus conservation efforts on those native species.

Natural Selection and Age-related Variation in Morphology of a Colonial Bird - Mary Brown

• Dissertation Defense
• 4/18/2011

In May 1996, inclement weather led to the deaths of thousands of Cliff Swallows (Petrochelidon pyrrhonota) in Nebraska. Survivors had larger skeletons, shorter wings and tails, and less wing asymmetry than non-survivors. This population was followed for 10 years to study 1) whether natural selection events result in permanent microevolutionary changes, 2) if variation in climate affects the development of morphological traits, and 3) if morphological traits vary systematically with age.

Patterns in morphology exhibited by swallows following the selection event were studied by measuring yearling birds. Wing and middle tail lengths decreased, beak length and width increased, tarsus length was unchanged, and the amount of wing asymmetry increased. The cumulative directional change in wing, tail, and beak length was greater after the selection event than during the event. This variation was not explained by phenotypic plasticity resulting from better environmental conditions, because conditions were not significantly different before and after the event. There was no evidence opposing selection restored skeletal size or wing or tail length to that before the selection event. This continued change in morphology may represent the population shifting to a different fitness peak in the adaptive landscape.

The way variation in climatic conditions (and food resources) affects the morphological development of juvenile swallows was studied. In cooler years birds allocated less growth to wings and tails than they did in warmer years, while maintaining normal levels of skeletal growth and body mass. Changes in juvenile feather growth in response to rearing conditions persisted into the first breeding season.

The extent morphological traits vary with age across a bird's lifetime was examined. Juveniles had shorter wings and tails, lower body mass, smaller skeletal size and lower levels of fluctuating asymmetry than adults. Among adult age classes, wing and tail length increased with age and wing and tail fluctuating asymmetry decreased with age. There was no evidence for degenerative senescence in swallows, as the decline in fluctuating asymmetry suggests the oldest birds maintain high levels of phenotypic performance. This age-related variation in morphology suggests that age should be considered in future analyses of morphological variation in passerines.

Nest and brood survival and habitat selection of ring-necked pheasants and greater prairie-chickens in Nebraska - Ty Matthews

• Dissertation Defense
• 11/13/2009

n/a

Evaluation and Application of Predictive Habitat Modeling in Ecology - Justin Hoffman

• Dissertation Defense
• 4/21/2008

My dissertation research is an important contribution to the growing field of predictive habitat modeling in ecology. I investigate innovative approaches for evaluating the performance of different predictive habitat models and applying these methods to large scale ecological phenomena. Several predictive habitat models currently exist. It has been the focus of much research to determine which is the best model(s). However, much of this research is undermined by biased data sets. To resolve this issue, I tested model performance with simulated data that is not prone to the usual biases of real data sets. In general, my results support the findings of previous studies in that models that accurately predicted species distributions with real occurrence data also showed superior performance using simulated occurrence data. Using the conclusions from the model evaluation analysis as a basis, I applied these methods to two independent research questions. I first identified certain variables that best predicted the occurrence of chronic wasting disease (CWD) in Nebraska. Chronic wasting disease is a newly emerging infectious disease found only in members of the deer family (Family Cervidae). Analysis of several different combinations of spatial, temporal, and environmental variables showed that the chance of recording a positive CWD case was greater the more time spent sampling and when that sampling was conducted in western Nebraska. For the second question, I predicted range expansion among six North American mammals and ascertaining what role environmental variables have in predicting those expansions. I used two predictive habitat models combined with climate, land cover, and elevation variables to predict distributions. I predicted range expansions accurately for two of the six species, suggesting that other factors influenced the distributions of the remaining species. My results demonstrate the applicability of predictive habitat modeling in ecology and provide insights into novel methods of evaluating model performance.