Combining demographic and count-based approaches to identify source-sink dynamics of a threatened seabird.

Identifying source-sink dynamics is of fundamental importance for conservation but is often limited by an inability to determine how immigration and emigration influence population processes. We demonstrate two ways to assess the role of immigration on population processes without directly observing individuals dispersing from one population to another and apply these methods to a population of Marbled Murrelets (Brachyramphus marmoratus) in California (USA). In the first method, the rate of immigration (i) is estimated by subtracting local recruitment (recruitment from within the population due to reproduction) estimated with demographic data from total recruitment (f; recruitment from within the population plus recruitment from other populations) estimated using temporal symmetry mark-recapture models developed by R. Pradel. The second method compares population growth rates estimated with temporal symmetry models (lambdaTS) and/or population growth rates estimated from counts of individuals over multiple sampling periods (lambdaC) with growth estimates from a stage-structured projection matrix model (lambdaM). Both lambdaTS and lambdaC incorporate all demographic processes affecting population change (birth, death, immigration, and emigration), whereas matrix models are usually constructed without incorporating immigration. Thus, if lambdaTS and lambdaC are > or = 1 and lambdaM < 1, the population is sustained by immigration and is considered to be a sink. Using the first method, recruitment estimated with temporal symmetry models was high (f= 0.182, SE = 0.058), the mean adult birth rate, as estimated using the ratio of juveniles to > or = 1 year old individuals (observed during ship-based surveys) was low (bA = 0.039, SE = 0.014), and immigration was 0.160 (SE = 0.057). Using the second method, murrelet numbers in central California were stable (lambdaC = 1.058, SE = 0.047; lambdaTS = 1.064, SE = 0.033), but were projected to decline 9.5% annually in the absence of immigration (lambdaM = 0.905, SE = 0.053). Our results suggest that Marbled Murrelets in central California represent a sink population that is stable but would decline in the absence of immigration from larger populations to the north. However, the extent to which modeled immigration is due to permanent recruitment or temporarily dispersing individuals that simply mask population declines is uncertain.     

Making Sense of the Policy Process for Carnivore Conservation

Grizzly bears ( Ursus arctos horribilis ), mountain lions ( Puma concolor ), wolverines ( Gulo gulo ), wolves ( Canis lupus ), and lynx ( Felis lynx ) are all top-level carnivores in the Rocky Mountains of the northern U.S. and southern Canada. Because of their body size and high trophic position, these species require abundant prey species and large habitat areas—requirements that make their conservation a controversial public policy problem. Because the challenge of conserving these species extends beyond biological issues, it is necessary to involve other relevant disciplines and perspectives in understanding and solving the problem. Our examination of the context, content, and process of large carnivore conservation policies suggests more effective and active roles for scientists in designing solutions to the problem of landscape-level carnivore conservation. Scientists must develop an understanding of the range of participants in the policy process and the ways in which these participants receive and utilize information. This knowledge of the policy process could help scientists to better understand their roles in framing and clarifying policy questions, projecting the consequences of various alternatives, and presenting policy information in appropriate fora.     

Newly metamorphosed <Emphasis Type="Italic">Elysia clarki</Emphasis> juveniles feed on and sequester chloroplasts from algal species different from those utilized by adult slugs

The adult, sacoglossan sea slug, Elysia clarki (Pierce et al. in Molluscan Res 26, 2006), sequesters functional chloroplasts in cells of the digestive diverticula from four species of macroalgae in the order Bryopsidales (Penicillus capitatus, Penicillus lamourouxii, Halimeda incrassata, and Halimeda monile). Feeding experiments were conducted in December, 2003, using individuals raised in the laboratory from egg masses laid by E. clarki adults which had been collected from Grassy Key, Florida, USA, and 29 species of macroalgae collected from the Florida Keys, Tampa Bay, Tarpon Springs, Florida, or Woods Hole, Massachusetts or obtained from the Culture Collection of Algae at the University of Texas at Austin, Texas. For the first 14-day post-metamorphosis, juveniles ate only the thin filamentous species, Bryopsis plumosa or Derbesia tenuissima. Transmission electron microscopy showed that the chloroplasts from both algae were sequestered intracellularly in juvenile slugs. Individuals offered any other macroalga, including the four species fed on by adults, did not feed on or incorporate any chloroplasts, and soon died. Juveniles switched from B. plumosa to P. capitatus at a length of ∼ 1.0 cm, and fixed for microscopy 14 days later had intact intracellular chloroplasts from both algae. Nucleotide sequences of the chloroplast gene, rbcL, from DNA extracted from E. clarki, collected from Vaca Key, Florida, were aligned with 22 other available macroalgal rbcL sequences indicating that these E. clarki adults had fed on three species of algae in the Bryopsidales including Bryopsis pennata, and TEM results partially confirmed this conclusion.     

Behaviour and physiology of sockeye salmon homing through coastal waters to a natal river

Adult sockeye salmon (Oncorhynchus nerka, N = 179) from six Fraser River populations (British Columbia) were intercepted in continental shelf waters ∼215 km from the Fraser River mouth, gastrically implanted with acoustic transmitters, non-lethally biopsied for blood biochemistry, gill Na⁺,K⁺-ATPase activity and somatic energy density and then released. Migration behaviour and travel times to the river mouth and into the river were monitored by underwater telemetry receivers positioned at the river mouth and in the river. Post-release survival of salmon was excellent, with 84% (N = 150) of fish reaching the furthest receiving station ∼85 km upriver. Fish from Late-summer run populations (Adams and Weaver Creek) averaged a migration rate of ∼20 km day⁻¹ through the marine area and held at the river mouth and adjacent areas for 7–9 days before entering the river. Summer-run populations (Birkenhead, Chilko, Horsefly and Stellako) had a migration rate ∼33 km day⁻¹ and held for only 1–3 days. Once in river, similar patterns were observed: Late-run populations migrated at ∼28 km day⁻¹ and Summer-run populations at ∼40 km day⁻¹. From point of release to the river mouth, males migrated faster than females, but once in river migration rates did not differ between sexes. Among all females, a correlation was discovered between levels of circulating testosterone and river entry timing. This correlation was not observed among males. Plasma K⁺, Cl⁻, glucose, lactate and osmolality were also correlated with entry timing in both sexes.     

A stage-structured, Aedes albopictus population model

Aedes albopictus has been the fastest spreading invasive animal species in the world from the mid-1980s until the mid-2000s. In areas it infests, it disrupts native mosquito ecology and can potentially vector up to 21 viruses. To better understand the population dynamics of this species, we created a temperature dependent population model. A stage-structured model was chosen to allow each life-stage to have different temperature dependent mortality and development rates, and each stage was modeled with an ordinary differential equation. Model parameters and distributions were based upon literature values. Initially, a basic model was constructed. This model then had parameters that were forced based upon daily average temperatures. Several criteria were used to evaluate the model, including a comparison to field data from Lubbock, TX. In a stochastic version of the model, a 95% confidence limit contained 70.7% of the field data points. Based upon these results, we feel reasonably confident that we have captured the role of temperature in driving the population dynamics of Ae. albopictus.     

Field evidence for pervasive indirect effects of fishing on prey foraging behavior

The indirect, ecosystem-level consequences of ocean fishing, and particularly the mechanisms driving them, are poorly understood. Most studies focus on density-mediated trophic cascades, where removal of predators alternately causes increases and decreases in abundances of lower trophic levels. However, cascades could also be driven by where and when prey forage rather than solely by prey abundance. Over a large gradient of fishing intensity in the central Pacific's remote northern Line Islands, including a nearly pristine, baseline coral reef system, we found that changes in predation risk elicit strong behavioral responses in foraging patterns across multiple prey fish species. These responses were observed as a function of both short-term ("acute") risk and longer-term ("chronic") risk, as well as when prey were exposed to model predators to isolate the effect of perceived predation risk from other potentially confounding factors. Compared to numerical prey responses, antipredator behavioral responses such as these can potentially have far greater net impacts (by occurring over entire assemblages) and operate over shorter temporal scales (with potentially instantaneous response times) in transmitting top-down effects. A rich body of literature exists on both the direct effects of human removal of predators from ecosystems and predators' effects on prey behavior. Our results draw together these lines of research and provide the first empirical evidence that large-scale human removal of predators from a natural ecosystem indirectly alters prey behavior. These behavioral changes may, in turn, drive previously unsuspected alterations in reef food webs.     

Forest Restoration on a Closed Landfill: Rapid Addition of New Species by Bird Dispersal

Urban areas often contain sizeable pockets of degraded land, such as inactive landfills, that could be reclaimed as wildlife habitat and as connecting links to enhance remnant natural areas. In the northeastern U.S., many such lands fail to undergo natural succession to woodland, instead retaining a weedy, herbaceous cover for many years. We hypothesize that seed dispersal is a limiting factor, and that a form of secondary succession could be stimulated by introducing clusters of trees and shrubs to attract avian seed dispersers. As a direct test, we censused a 1.5-ha experimental plantation on the Fresh Kills Landfill (Staten Island, New York) one year after installation, in search of evidence that the plantation was spreading or increasing in diversity. The 17 planted species, many from coastal scrub forests native to this region, were surviving well but contributed almost no seedlings to the area, in part because only 20% of the installed trees or shrubs were reproductive. Of the 1079 woody seedlings found, 95% came from sources outside the plantation; most (71%) were from fleshy-fruited, bird-dispersed plants from nearby woodland fringes. Although the restoration planting itself had not begun to produce seedlings, it did function as a site for attracting dispersers, who enriched the young community with 20 new species. One-fourth of all new recruits were from nine additional wind-dispersed species. Locations with a high ratio of trees to shrubs had proportionately more recruits, indicating that plant size contributed to disperser attraction. The density of new recruits of each species was dependent on distance from the nearest potential seed source. Introducing native species with the capacity to attract avian dispersers may be the key to success of many restoration programs.