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Bodega Marine Laboratory/Reserve
February 26-28, 2010 |
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Participant Abstracts
Raiding behavior in an obligate slave-making ant
Joe Sapp
Department of Ecology and Evolutionary Biology
University of California, Santa Cruz
Social parasites are a powerful system to study many aspects of host-parasite interactions. The socially parasitic “slave-making” ant Polyergus breviceps raids neighboring nests to capture brood (larvae and pupae) from several species of ant in the genus Formica. These stolen brood are reared to adulthood by existing Formica “slaves” and become workers for the P. breviceps nest, which they mistake as their own due to chemical imprinting. My research focuses on two aspects of the raiding behavior of P. breviceps. First, I investigate how colonies allocate resources to raids and how these allocations affect raid success. By videotaping raid columns, I can estimate raid efficiency, resource allocation, and raid success among several neighboring nests. Second, I am interested in the factors that mediate competition among
slave-maker nests. Though P. breviceps is described as highly aggressive towards conspecifics
elsewhere, preliminary data suggests a more complicated picture: Conspecific raids do occur, usually with the ultimate destruction of the raided colony. However, raid ranges appear to overlap extensively among P. breviceps nests and occasionally raids from different nests cross each other with no visible interaction between raiders. I suspect that relatedness and host preference both play a role in the observed spatial pattern of raids and the range of interactions observed among neighboring P. breviceps nests.
Christopher Briggs
Department of Entomology
University of California, Riverside
The coastal sage scrub vegetation type (CSS) is an excellent setting for investigating harvester ant
interactions with exotic plant seeds; harvester ants are abundant in CSS, and CSS is frequently invaded by several exotic plant species. Exotic plants in CSS change fire frequency, soil hydrology, and other ecosystem properties, potentially harming several endangered species found there. Harvester ants can be the dominant seed predators on plants by collecting and eating seeds, and they are known to influence plant communities. This study focuses on the harvester ant Pogonomyrmex rugosus to determine what seeds P. rugosus foragers collect in CSS, and whether P. rugosus foragers exhibit preferences for
particular plant species. Observations show that P. rugosus carried seeds of exotic Erodium cicutarium and Brassica tournefortii on 11% and 46% (respectively) of return trips to the nest, and only a very few carried native seeds such as Encelia farinosa. When compared to the proportions of seed species found in the field, P. rugosus showed preference against E. farinosa and B. tournefortii, and preference for E.
cicutarium. Cafeteria-style experiments confirmed these preferences and also showed that native
Eriogonum fasciculatum seeds were preferred even less than E. farinosa and B. tournefortii. Thus, P.
rugosus in CSS has frequent interactions with exotic E. cicutarium and B. tournefortii, involving the
movement and likely destruction of large numbers of seeds. Future studies may be able to determine
whether seed collection by P. rugosus constitutes a significant predation pressure on E. cicutarium and B. tournefortii populations.
Sarah Dalrymple
Population Biology Graduate Group
University of California, Davis
Plants in fire-prone landscapes often have adaptations that allow them to cope with fire damage. For example, Jeffrey pines have thick bark and self-pruned branches that resist heat damage and prevent fires from spreading to the tree crown. Recent observations indicate that a more indirect fire-resistance strategy also exists for Jeffrey pines. Following fires, ring-shaped clearings, free of litter, are maintained around tree trunks, even when needles accumulate elsewhere on the forest floor. Evidence from the 2007 Angora Fire in South Lake Tahoe suggests that these clearings reduce both damage and mortality to trees. Therefore, determining the forces responsible for maintaining clearings is crucial to understanding a novel mechanism of fire resistance in trees. In the Inyo National Forest south of Mono Lake, 74 (± 24)% of trees in recently burned forest have clearings compared to 18 (± 12)% in unburned forest. Thus fire likely initiates clearing formation and clearings were probably common under natural fire regimes. Abiotic factors, such as wind and stem flow, probably influence clearings, but ants may also play a role in maintaining clearings around trees. The ant Formica sibylla prefers exposed nest sites and is found nesting in a majority of clearings (62 ± 19%) in sampled plots. Experiments run over the last two summers suggest that ants may play a role in removing needles deposited in clearings, but that this behavior is not contingent on the ants having an active nest entrance in the clearing. Future work will focus on the importance of clearings to ants.
Thomas C. Smith
Department of Ecology, Evolution, and Marine Biology
University of California, Santa Barbara
The current rate and scale of species declines and extinctions are comparable to those of previous mass extinction events. Amphibians in particular have suffered dramatic mortality from anthropogenic disturbances such as habitat destruction and introduction of invasive species, as well as natural stressors such as emerging infectious disease. These declines translate to losses of consumer abundance and biomass in freshwater and terrestrial communities. Due to the ontogenic diet shifts associated with amphibian metamorphosis, these losses frequently occur across two trophic levels and are akin to loss of two species from communities. This suggests that amphibian declines and extinctions will have notable effects on communities. To assess the role of declining mountain yellow-legged frogs in alpine lake communities of the Sierra Nevada and potential effects of local extinctions, a two consumer-single resource experiment was conducted from mid-July to mid-September 2009. Earlier data indicated natural densities of the dominant primary consumers in Sierra lakes, and this data was used to establish experimental densities of mayfly larvae and tadpoles, which were placed in seventeen enclosures in each of two lakes in the Sierra backcountry. Biomass and growth rate of benthic producers and each consumer were measured, and will be compared to quantify the impact of each consumer on the resource, and to detect and measure competitive interactions. In addition, a concurrent long-term observational study will compare lake nutrient concentrations, algal production and diversity, and macroinvertebrate diversity to amphibian density and disease status in a dozen lakes over several years.
Christopher Searcy
Department of Evolution and Ecology
University of California, Davis
Due to the fossorial nature of ambystomatid salamanders, few studies have captured these species in the terrestrial landscape. This has made it difficult to learn about demography and metapopulation dynamics among non-breeding stages of this group. Using a drift-fence array that stretches up to one kilometer from the edge of their breeding pond, we investigated survival between non-breeding stages of the California
tiger salamander and dispersal of this species into the terrestrial environment. Tracking individual
salamanders was made possible through the use of a pattern recognition program and subdermal
alphanumeric tags. Implanting 2,335 metamorphs and photographing 3,114 adults and juveniles yielded 850 recapture events. These data revealed that larger individuals are more likely to survive between years during both the adult and juvenile stages, and are more likely to reach maturity from the juvenile stage. In addition, larger metamorphs disperse farther from the breeding pond. The importance of these trends is seen in the fact that average metamorph mass in the 18 cohorts examined in this study varied almost threefold between 5.3 g and 14.78 g. Thus, the average individual in the largest cohort has an 18-fold higher probability of surviving to maturity and will disperse 550 m further from the breeding pond than the average individual in the smallest cohort. This will introduce huge temporal variation into the population dynamics of this species, with certain cohorts having a much higher probability of contributing individuals to future generations and contributing dispersers to neighboring breeding ponds.
Adrienne B. Mora
Department of Evolution, Ecology, and Organismal Biology
University of California, Riverside
Many parasites adaptively alter host biology to maximize transmission and completion of their life cycles (termed “host manipulation”) at the expense of host fitness. In parasite-increased trophic transmission, the behavior of an intermediate host is modified to facilitate predation by a final host, often by intensifying a risky behavior that makes the host more conspicuous to a predator. Generally, parasites that employ this strategy are under strong selection to optimize transmission by predation, because they only reach sexual maturation and reproduce in the predatory final host. Although host manipulation is known to confer fitness advantages for parasites, cases of manipulation that enhance components of host fitness are not known. However, if the modified host behavior is used in mate attraction, then parasitism can provide short-term benefits to the host by intensifying a sexually selected signal. This presents a paradox, for parasites may shorten the life span of hosts by increasing susceptibility to predation, but they could increase their short-term reproductive success by intensifying behaviors used in mate acquisition. Using field and laboratory studies, I will examine how trophically transmitted parasites influence sexual signaling in fiddler crabs, and the effects that these interactions have on host mating success. Results from this work will help elucidate how parasites influence the evolution of host sexual signals, and may reveal a new role for parasites in sexual selection.
H. W. Weiskel
1 Byers, J.E.,2 Huspeni, T.C.,3 Zabin, C.J.,4 Bowles, C.M.,1 Brown, C.,4 and E.D. Grosholz.1
1 University of California, Davis
2 University of Georgia
3 University of Wisconsin, Stevens Point
4 Smithsonian Environmental Research Center
Few data exist describing founder populations in marine systems. New invasions can elucidate founder processes, but are frequently not detected until populations are well-established. In April 2007, we
discovered the first known population of Batillaria attramentaria, a mud snail native to Japan, in Bodega Harbor, California. This discovery offers an opportunity to investigate early invasion dynamics of a species that has been detrimental to West Coast mudflat communities for decades. In addition to obtaining
demographic data, we also initiated an eradication effort. Field surveys from 2007-2009 show a steady increase in mean densities and a modal size class shifting towards smaller individuals (from 10-14.99 mm to 5-9.99 mm), reflecting strong recruitment. Rates of trematode parasitism have increased from 0-7.5% in the size class at which the snails are most likely to first become infected (20-24.99 mm), but have
decreased in the overall population. This pattern contrasts sharply with infection rates of 42% in an
established population in Tomales Bay. The Bodega Harbor results are consistent with an increase in the proportion of juvenile snails in a successfully establishing population. Approximately 22,000 and 19,000 adult snails were removed by hand in 2007 and 2008, respectively, as part of the eradication effort. New techniques are currently being tested, including vacuum collection for more effective surficial snail
removal. The results from this population characterization and eradication effort will further our
understanding of founder populations of invasive species and permit evaluation of eradication efforts in soft sediments.
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