Browsing by Subject "Animal movement"

Infusing models for animal movement with more behavioral realism has been a goal of movement ecologists for several years. As ecologists have begun to collect more and more data on animal distribution and abundance, a clear need has arisen for more sophisticated analysis. Such analysis could include more realistic movement behavior, more information on the organism-environment interaction, and more ways to separate observation error from process error. Because landscape ecologists and behavioral ecologists typically study these same themes at very different scales, it has been proposed that their union could be productive for all (Lima and Zollner, 1996).

By understanding how animals interact with their land- and seascapes, we can better understand how species partition up resources are large spatial scales. Accordingly I begin this dissertation with a large spatial scale analysis of distribution data for marine mammals from Nova Scotia through the Gulf of Mexico. I analyzed these data in three separate regions, and in the two data-rich regions, find compelling separation between the different communities. In the northernmost region, this separation is broadly along diet based partitions. This research provides a baseline for future study of marine mammal systems, and more importantly highlights several gaps in current data collections.

In the last 6 years several movement ecologists have begun to imbue sophisticated statistical analyses with increasing amounts of movement behavior. This has changed the way movement ecologists think about movement data and movement processes. In this dissertation I focus my research on continuing this trend. I reviewed the state of movement modeling and then proposed a new Bayesian movement model that builds on three questions of: behavior; organism-environment interaction; and process-based inference with noisy data.

Application of this model to two different datasets, migrating right whales in the NW Atlantic, and foraging monk seals in the Northwest Hawaiian Islands, provides for the first time estimates of how moving animals make choices about the suitability of patches within their perceptual range. By estimating parameters governing this suitability I provide right whale managers a clear depiction of the gaps in their protection in this vulnerable and understudied migratory corridor. For monk seals I provide a behaviorally based view into how animals in different colonies and age and sex groups move throughout their range. This information is crucial for managers who translocate individuals to new habitat as it provides them a quantitative glimpse of how members of certain groups perceive their landscape.

This model provides critical information about the behaviorally based movement choices animals make. Results can be used to understand the ecology of these patterns, and can be used to help inform conservation actions. Finally this modeling framework provides a way to unite fields of movement ecology and graph theory.

Sea turtles have experienced dramatic population declines during the last century as a consequence of direct harvest, by-catch in fisheries, and habitat loss. Despite almost 50 years of partial international protection, several populations of sea turtles are still at imminent risk of extinction. Our knowledge of their complex life histories is still far from complete; these knowledge gaps hinder our ability to provide scientific advice regarding their conservation and management. It is the very complexity of their life histories, which allows them to exploit widely separated habitats during development, often over the course of decades, which makes them inherently difficult to study. I used satellite telemetry (n=60) to investigate the movements and habitat use patterns of juvenile loggerhead (Caretta caretta), green (Chelonia mydas), and Kemp's ridley (Lepidochelys kempii) sea turtles on their summer feeding grounds in North Carolina estuaries. These turtles migrate into and out of the estuarine waters each spring and autumn, encountering a gauntlet of fishing gear on each journey. The by-catch of sea turtles is an important conservation issue in North Carolina, and throughout the world's oceans. I evaluated conservation measures established to reduce the by-catch of sea turtles in Pamlico Sound's autumnal large-mesh gill net fishery for southern flounder (Paralichthys lethostigma), using a spatially explicit predator/prey model. My findings indicated that species-specific habitat preferences contributed to a turtles' risk of encountering fishing gear and that areas of high by-catch are predictable from patterns of overlap between sea turtle habitat use and flounder fishing effort. I then examined how the behavior of green turtles affected their vulnerability to incidental capture in estuarine commercial fisheries. Individual green turtles interact with multiple gears per season as a result of strong site fidelity to habitats also preferred by fishers. Telemetry also allowed me to examine individual variation in movements, habitat use, and site fidelity patterns of juvenile loggerhead turtles, both within the estuary and as the turtles migrated out into the North Atlantic. I used these observations to test the hypothesis of a discrete ontogenetic shift in habitat and diet in juvenile loggerheads. Approximately one-third of large juvenile loggerheads tagged in North Carolina estuaries return to oceanic habitat, sometimes for several years, where they are vulnerable to by-catch in pelagic fisheries. This led me to conclude that the long held notion of a discrete ontogenetic habitat shift between the oceanic and neritic habitat was incorrect for juvenile loggerheads (and possibly also for green turtles). Finally, I explored variation in migratory destinations in these animals through multivariate analyses of carbon and nitrogen stable isotope ratios in blood plasma and red blood cells, and through analysis of sex, genetic, haplotype, body size, and remigration records, and described the trophic niche of these turtles with Bayesian isotope mixing models. Variation in migratory destination (oceanic or neritic habitat) was best described by stable isotope ratios of nitrogen and remigration tendency. Turtles that returned to the open ocean had significantly lower nitrogen ratios than those animals that remained in the neritic zone and their diets retained a substantial contribution of epipelagic prey items. The diet composition of neritic turtles, on the other hand, consisted primarily of estuarine benthic invertebrates during the summertime and autumn foraging season but shifted toward pelagic jellyfish, fish, and Sargassum during the overwintering period. Oceanic turtles likely came from open ocean regions prior to entering the summer foraging grounds while neritic turtles likely overwintered at the edge of the Gulf Stream. The agreement between the dietary compositions and migration patterns between the two groups of turtles suggest that these feeding and habitat use strategies were persistent characteristics in the turtles I sampled. My work has improved our understanding of sea turtle habitats in North Carolina estuaries and identified their migratory destinations and overwintering habitats. I hope that this work lays the groundwork for future studies that will explore how variation in habitat use and feeding strategies are manifested in life history traits that affect fitness directly, such as survivorship, growth rates, stage durations, and fecundity.

To conserve biodiversity, it is critical to understand the dynamic landscapes and climates through which species move and how the environment influences movement choices. In particular, I am interested in how species respond to human modifications to landscapes and climates. Chapter 1 uses datasets on the spatial and temporal coverage of remotely sensed land cover datasets to examine gaps in the monitoring of environmental priorities. Temporal gaps in Landsat and spatial gaps in commercial high resolution satellites such as QuickBird may hinder land cover change monitoring efforts.

Chapter 2 uses Global Climate Models and museum specimens to projects the impact of climate change on the flora of California, a global biodiversity hotspot. With anticipated climate change, up to 66% may experience >80% reductions in range size within a century. These projections are less severe if plants are able to disperse in time. With no constraints on dispersal, plant centroids move an average of up to 150 km. The projections identify regions where species undergoing severe range reductions may persist. Protecting these potential future refugia and facilitating species dispersal may be essential to maintain biodiversity in the face of climate change.

Chapter 3 analyzes the movements of 73 elephants fitted with GPS collars against 4 remotely sensed datasets spanning a strong rainfall gradient across 7 southern African countries. Movements show strong seasonal and geographic differences across the study area. Two major human interventions, artificial water and fences, distort these movement patterns by increasing dry season ranging patterns and increasing the density of wet season movements.

Chapter 4 uses the datasets described in chapter 3 to explore elephant vegetation preferences. Elephants consistently prefer greener vegetation throughout the year. Vegetation preferences vary seasonally. Elephants prefer less variable vegetation such as forests in the dry season and ephemeral vegetation such as grasslands in the wet season.

Chapter 5 uses telemetry and remotely sensed landcover data to ask how climatic factors - snow cover - and land cover - agriculture and roads - influence pronghorn movements in South Eastern Alberta. Analysis using a Bayesian movement model reveals that each of these features significantly influences pronghorn movement choices.

The ultimate goal of wildlife recovery is abundance growth of a species, though it must also involve the reestablishment of the species’ ecological role within ecosystems frequently modified by humans. Reestablishment and subsequent recovery may depend on the species’ degree of adaptive behavior as well as the duration of their functional absence and the extent of ecosystem alteration. In cases of long extirpations or extensive alteration, successful reestablishment may entail adjusting foraging behavior, targeting new prey species, and encountering unfamiliar predatory or competitive regimes. Recovering species must also increasingly tolerate heightened anthropogenic presence, particularly within densely inhabited coastal zones. In recent decades, gray seals (Halichoerus grypus) recovered from exploitation, depletion, and partial extirpation in the Northwest Atlantic. On Cape Cod, MA, USA, gray seals have reestablished growing breeding colonies and seasonally interact with migratory white sharks (Carcarodon carcharias). Though well-studied in portions of their range due to concerns over piscivorous impacts on valuable groundfish, there are broad knowledge gaps regarding their ecological role to US marine ecosystems. Furthermore, there are few studies that explicitly analyze gray seal behavior under direct risk of documented shark predation.

In this dissertation, I apply a behavioral and movement ecology approach to telemetry data to understand gray seal abundance and activity patterns along the coast of Cape Cod. This coastal focus complements extensive research documenting and describing offshore movement and foraging behavior and allows me to address questions about movement decisions and risk allocation. Using beach counts of seals visible in satellite imagery, I estimate the total regional abundance of gray seals using correction factors from haul out behavior and demonstrate a sizeable prey base of gray seals locally. Analyzing intra-annual space use patterns, I document small, concentrated home ranges utilizing nearshore habitats that rapidly expand with shifting activity budgets to target disperse offshore habitats following seasonal declines in white sharks. During the season of dense shark presence, seals conducted abbreviated nocturnal foraging trips structured temporally around divergent use of crepuscular periods. The timing of coastal behavior with different levels of twilight indicate risk allocation patterns with diel cycles of empirical white shark activity. The emergence of risk allocation to explain unique behavioral and spatial patterns observed in these gray seals points to the importance of the restored predator-prey dynamic in gray seal behavior along Cape Cod.