Bodega Marine Laboratory/Reserve
March 2-4, 2012 |
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Participant Abstracts
Images credit: Michael Dorward
Keith Gaddis
Department of Ecology and Evolutionary Biology
University of California, Los Angeles
In the face of human-driven environmental change, ecology and conservation biology are increasingly concerned with factors influencing population dynamics. Species distributed among patches may be particularly sensitive to change due to constraint by niche limitations or resource competition. Increasing distance between patches due to environmental damage could lead to a decline in recolonization probability, resulting in decreased local stability. Areas like the American southwest are currently at an increased risk, as multiple climate models have predicted increasing aridity over the next 50 years and large areas are now slated for development of solar power plants, destroying huge areas of preserved land and cutting off remaining populations. In this environment, we have used
Acacia greggii A Gray as a model of limitations to reproduction and gene flow in both a historical and contemporary context. We are investigating the mechanisms that maintain dispersal across such a heterogeneous landscape where populations are separated by mountain ranges and dry valleys. Using molecular techniques, we have documented a history of widespread gene flow in this species over the range of the preserve, but identified a more limited movement currently. We are quantifying the influence of dry washes on connectivity patterns in this species. It is possible that monsoon events in this region have driven rapid movement and new establishment of A.
greggii. This analysis will inform us as to how this and other species will respond to a future of increasingly infrequent rainfall patterns.
Image credit: Michael Dorward
Bruce Hammock
Graduate Group in Ecology
University of California, Davis
Determining how environmental problems interact with one another to affect ecosystems is a first step toward mitigation. Streams in the Sierra Nevada Mountains are subjected to ongoing climate change and are heavily invaded by exotic trout. Because trout metabolism will likely increase as alpine streams warm, the effect of trout on community structure and function may increase in response to climate change. We asked how an ecosystem function, the daytime drift of a stream mayfly, responds to changes in water temperature, and whether that response varied between streams invaded and uninvaded by trout. Specifically, we show that the daytime drift of Baetis tricaudatus exhibits a strong, negative correlation with water temperature in a fish-bearing stream, and demonstrate experimentally that water temperature was a probable driver for this correlation. Then, in an experiment replicated at the catchment scale, we show that water temperature and fish presence strongly interact to affect the daytime drift of Baetis bicaudatus. In fishless streams, daytime drift increased with water temperature, while in fish-bearing streams, daytime drift decreased with water temperature. Our results suggest that the anticipated increase in stream temperature due to climate change may escalate observed divergence in community structure and function between invaded and uninvaded streams, and that managers could reduce the effects of climate change by removing exotic trout.
Image credit: Michael Dorward
Kirsten E. Hill
Department of Environmental Science, Policy, and Management
University of California, Berkeley
Predators can play a critical role in the structure and function of ecosystems through trophic cascades. In California’s introduced annual grasslands, arthropod predators’ ability to forage may be altered by non-native grasses that have different life forms than the formerly dominant native perennial grass. Land managers challenged to restore and maintain these systems have a task complicated by the inherent unpredictability of the indirect interactions found in trophic cascades. It is unknown if habitats dominated by non-native grasses reduce the abundance and diversity of arthropods. I hypothesized that senescent, non-native annual grasses create a hot, dry landscape, inducing herbivorous arthropods to switch from non-native to native food plants and reducing spider survival and foraging when compared to spiders in native perennial habitats. Using diurnal observational surveys and pitfall trapping along 30 m meadow boundary to interior transects, I found a significant positive correlation (r =.786) between the percent of native plant species and the abundance of arthropods present. Total spiders captured in pitfall traps was also significantly correlated (r =.881) with an increasing percent of native plant species. A significant positive effect was found with the proportion of native grass and distance from shaded meadow boundary on total spiders captured in pitfall traps for distances of 0, 15, 20, and 30 m from meadow boundary, with more spiders in native grasses. Knowledge from this study will benefit not only researchers but also land managers and planners who together face the daunting challenge of trying to keep and restore our remaining grasslands.
Images credit: Micheal Dorward
Gilene M. Young
Department of Ecology and Evolutionary Biology
University of California, Los Angeles
Differences in reproductive tactics and phenotypes are most often explained in the adaptive context of frequency-dependent and condition-dependent selection. However, traditional theories relating ecology and mating systems do not account for the effects that the behavior of one sex can have on the fitness of the other. Sand wasps (Crabronidae: Bembicinae) present a unique opportunity to study the importance of phenotypic variation in sexual interactions, because there is variability in sexual dimorphism and mating behavior across species. In particular, Steniolia nigripes shows reversed sexual size dimorphism and aggressive male defense of food resources visited by females, a behavior previously undescribed in the Bembicinae. Males are larger than females, but body size varies significantly within both sexes. If body size mediates the success of reproductive tactics, several patterns should be evident: (1) Large body size contributes to individual success in obtaining high quality territory or prey items; (2) the relative value and local distribution of body size vary with changes in resource availability; and (3) females and/or males demonstrate preferences in mating that correlate to either the size of the chooser or the size of the potential mate. My data indicate that male aggression level and success in territory holding are highly related to body size, confirming the first prediction. Body size may be a critical factor in determining the outcome of intrasexual competition, mate choice, and conflict between male and female reproductive behaviors in S. nigripes.
Melissa Grunst
Department of Evolution, Ecology, and Organismal Biology
University of California, Riverside
Adjustment of physiological mechanisms in response to external or internal cues allows for adaptive behavior. One physiological mechanism that mediates optimal balance of the survival-reproduction tradeoff is release of steroid hormones, glucocorticoids, via the adrenocortical stress response. Glucocorticoids act adaptively to promote glucose metabolism and flight-fight responses, but also have costs including muscle wasting and suppressed reproductive function. Indeed, down-regulation of the stress response facilitates energetic investment into reproduction by preventing cessation of reproductive activity despite potential survival threats. Down-regulation of the stress response during the breeding season is well documented among vertebrate taxa. However, despite profound fitness implications, intraspecific variation in stress hormones within the breeding season rarely has been studied. My research examines whether song sparrows (Melospiza melodia) display intraspecific differences in stress physiology that reflect variation in the value of the reproductive attempt, and which translate into differences in reproductive effort and responses to offspring- and adult-directed threats. To address this question, I am capturing sparrows using conspecific playback and measuring the stress response via serial blood sampling. I am also measuring variables that influence the value of the reproductive attempt including clutch size, time in the breeding season, and male quality (reflected by repertoire size). Finally, I am measuring reproductive effort by video-recording incubation attentiveness and nestling provisioning rates, in the presence and absence of nest and adult predator decoys. Preliminary results regarding effects of hormone levels on reproductive behavior are inconclusive, but suggest that male quality is an important factor influencing female reproductive effort.
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