Shifting elasmobranch community assemblage at Cocos Island—an isolated marine protected area

Fishing pressure has increased the extinction risk of many elasmobranch (shark and ray) species. Although many countries have established no‐take marine reserves, a paucity of monitoring data means it is still unclear if reserves are effectively protecting these species. We examined data collected by a small group of divers over the past 21 years at one of the world's oldest marine protected areas (MPAs), Cocos Island National Park, Costa Rica. We used mixed effects models to determine trends in relative abundance, or probability of occurrence, of 12 monitored elasmobranch species while accounting for variation among observers and from abiotic factors. Eight of 12 species declined significantly over the past 2 decades. We documented decreases in relative abundance for 6 species, including the iconic scalloped hammerhead shark (Sphyrna lewini) (?45%), whitetip reef shark (Triaenodon obesus) (?77%), mobula ray (Mobula spp.) (?78%), and manta ray (Manta birostris) (?89%), and decreases in the probability of occurrence for 2 other species. Several of these species have small home ranges and should be better protected by an MPA, which underscores the notion that declines of marine megafauna will continue unabated in MPAs unless there is adequate enforcement effort to control fishing. In addition, probability of occurrence at Cocos Island of tiger (Galeocerdo cuvier), Galapagos (Carcharhinus galapagensis), blacktip (Carcharhinus limbatus), and whale (Rhincodon typus) sharks increased significantly. The effectiveness of MPAs cannot be evaluated by examining single species because population responses can vary depending on life history traits and vulnerability to fishing pressure.     

A molecular genetic analysis of social structure, dispersal, and interpack relationships of the African wild dog (Lycaon pictus )

The African wild dog is a highly social, pack-living predator of the African woodland and savannah. The archetypal wild dog pack consists of a single dominant breeding pair, their offspring, and non-breeding adults who are either offspring or siblings of one of the breeding pair. Non-breeding adults cooperate in hunting, provisioning and the protection of young. From these observations follows the prediction that the genetic structure of wild dogs packs should resemble that of a multigenerational family, with all same-sexed adults and offspring within a pack related as sibs or half-sibs. Additionally, a higher kinship between females from neighboring packs should be evident if females tend to have small dispersal distances relative to males. We test these predictions through analysis of mitochondrial DNA control region sequences and 14 microsatellite loci in nine wild dog packs from Kruger National Park, Republic of South Africa. We show that as predicted, African wild dog packs generally consist of an unrelated alpha male and female, subdominant close relatives, and offspring of the breeding pair. Sub-dominant wild dogs occasionally reproduce but their offspring rarely survive to 1 year of age. Relatedness influences the timing and location of dispersal events as dispersal events frequently coincide with a change in pack dominance hierarchy and dispersers often move to areas with a high proportion of close relatives. Received: 22 February 1996 / Accepted after revision: 16 November 1996     

Development of a multi-factor model for predicting the effects of ambient ozone on the biomass of white clover

Results are presented from the UN/ECE ICP Vegetation (International Cooperative Programme on effects of air pollution on natural vegetation and crops) experiments in which ozone(O(3))-resistant (NC-R) and -sensitive (NC-S) clones of white clover (Trifolium repens cv. Regal) were exposed to ambient O(3) episodes at 14 sites in eight European countries in 1996, 1997 and 1998. The plants were grown according to a standard protocol, and the forage was harvested every 28 days for 4-5 months per year by excision 7 cm above the soil surface. Biomass ratio (NC-S/NC-R) was related to the climatic and pollutant conditions at each site using multiple linear regression (MLR) and artificial neural networks (ANNs). Twenty-one input parameters [e.g. AOT40, 7-h mean O(3) concentration, daylight vapour pressure deficit (VPD), daily maximum temperature] were considered individually and in combination with the aim of developing a model with high r(2) and simple structure that could be used to predict biomass change in white clover. MLR models were generally more complex, and performed less well for unseen data than non-linear ANN models. The ANN model with the best performance had five inputs with an r(2) value of 0.84 for the training data, and 0.71 for previously unseen data. Two inputs to the model described the O(3) conditions (AOT40 and 24-h mean for O(3)), two described temperature (daylight mean and 24-h mean temperature), and the fifth input appeared to be differentiating between semi-urban and rural sites (NO concentration at 17:00). Neither VPD nor harvest interval was an important component of the model. The model predicted that a 5% reduction in biomass ratio was associated with AOT40s in the range 0.9-1.7 ppm x h (microl l(-1) h) accumulated over 28 days, with plants being most sensitive in conditions of low NO(x), medium-range temperature, and high 24-h mean O(3) concentration.     

Effect of surface coatings, grain size, and ionic strength on the maximum attainable coverage of bacteria on sand surfaces

The injection of bacteria in the subsurface has been identified as a potential method for in situ cleanup of contaminated aquifers. For high bacterial loadings, the presence of previously deposited bacteria can result in decreased deposition rates--a phenomenon known as blocking. Miscible displacement experiments were performed on short sand columns (approximately 5 cm) to determine how bacterial deposition on positively charged metal-oxyhydroxide-coated sands is affected by the presence of previously deposited bacteria. Approximately 8 pore volumes of a radiolabeled bacterial suspension at a concentration of approximately 1 x 10(9) cells ml-1 were introduced into the columns followed by a 2-pore-volume flush of cell-free buffer. It was found that the presence of Al- and Fe-coated sand increased both deposition rates and maximum fractional surface coverage of bacteria on the sediment surfaces. The effect of grain size on maximum bacterial retention capacity, however, was not significant. Decreasing ionic strength from 10(-1) to 10(-2) M KCl resulted in noticeable decreases in sticking efficiency (alpha) and maximum surface coverage (thetamax) for clean silica sand--results consistent with DLVO theory. In columns containing positively charged Al- and Fe-coated sands, however, changes in alpha and thetamax due to decreasing ionic strength were minimal. These findings demonstrate the importance of geochemical controls on the maximum bacterial retention capacity of sands.     

Mercury levels in the plumage of red-billed gulls Larus novaehollandiae scopulinus of known sex and age

Samples of 4-8 small body feathers were taken from 27 chicks and 35 adult red-billed gulls caught at their nests on the Kaikoura Peninsula, New Zealand, in December 1988. The adults had been ringed as chicks and were of known ages from 2 to 15 years old. Analysis of total mercury in the feather samples showed that levels were independent of sex and age in adults. Mean fresh weight concentration in adult body feathers was 2.4 microg g(-1). The lack of age accumulation of mercury in gull feathers contrasts with the well known age related accumulation of mercury in tissues of fish and marine mammals, but agrees with predictions of recent studies on mercury dynamics in birds. Mercury levels in chick feathers were about 80% of levels in adult feathers.     

Shifting prey selection generates contrasting herbivore dynamics within a large-mammal predator-prey web

Shifting prey selection has been identified as a mechanism potentially regulating predator-prey interactions, but it may also lead to different outcomes, especially in more complex systems with multiple prey species available. We assessed changing prey selection by lions, the major predator for 12 large herbivore species in South Africa's Kruger National Park. The database was provided by records of found carcasses ascribed to kills by lions assembled over 70 years, coupled with counts of changing prey abundance extending over 30 years. Wildebeest and zebra constituted the most favored prey species during the early portion of the study period, while selection for buffalo rose in the south of the park after a severe drought increased their vulnerability. Rainfall had a negative influence on the proportional representation of buffalo in lion kills, but wildebeest and zebra appeared less susceptible to being killed under conditions of low rainfall. Selection by lions for alternative prey species, including giraffe, kudu, waterbuck, and warthog, was influenced by the changing relative abundance and vulnerability of the three principal prey species. Simultaneous declines in the abundance of rarer antelope species were associated with a sharp increase in selection for these species at a time when all three principal prey species were less available. Hence shifting prey selection by lions affected the dynamics of herbivore populations in different ways: promoting contrasting responses by principal prey species to rainfall variation, while apparently being the main cause of sharp declines by alternative prey species under certain conditions. Accordingly, adaptive responses by predators, to both the changing relative abundance of the principal prey species, and other conditions affecting the relative vulnerability of various species, should be taken into account to understand the interactive dynamics of multispecies predator-prey webs.     

The One-Migrant-per-Generation Rule in Conservation and Management

In the face of continuing habitat fragmentation and isolation, the optimal level of connectivity between populations has become a central issue in conservation biology. A common rule of thumb holds that one migrant per generation into a subpopulation is sufficient to minimize the loss of polymorphism and heterozygosity within subpopulations while allowing for divergence in allele frequencies among subpopulations. The one-migrant-per-generation rule is based on numerous simplifying assumptions that may not hold in natural populations. We examine the conceptual and theoretical basis of the rule and consider both genetic and nongenetic factors that influence the desired level of connectivity among subpopulations. We conclude that one migrant per generation is a desirable minimum, but it may be inadequate for many natural populations. We suggest that a minimum of 1 and a maximum of 10 migrants per generation would be an appropriate general rule of thumb for genetic purposes, bearing in mind that factors other than genetics may further influence the ideal level of connectivity.