Amphibian Declines: Judging Stability, Persistence, and Susceptibility of Populations to Local and Global Extinctions

Extinctions are normal biological phenomena. Both mass extinctions in geological time and local extinctions in ecological time are well documented, but rates of extinction have increased in recent years—especially in vertebrates, including amphibians—as illustrated by recent reports of their population declines and range reductions. We suggest that long-term population data are necessary for rigorously evaluating the significance of the amphibian declines. Due to the physiological constraints, relatively low mobility, and site fidelity of amphibians, we suggest that many amphibian populations may be unable to recolonize areas after local extinction.     

Sardine (Sardina pilchardus) spawning seasonality in European waters of the northeast Atlantic

Egg data from ichthyoplankton monitoring sites in the western English Channel (1988–2003) and northern Spain (1990–2000) and macroscopic maturity data from biological samples of purse seine landings in western and southern Iberia (1980–2004) are used to describe the spawning seasonality of sardine (Sardina pilchardus) in European waters of the northeast Atlantic using generalised additive models. The fitted models reveal a double peak in spawning activity during early summer and autumn in the western Channel, a wider spring peak off northern Spain and a broad winter season in the western and southern Iberian Peninsula. At all sites, a high probability of spawning activity was observed over at least 3 months of the year, with the duration of the season increasing with both decreasing latitude and increasing fish size. Off western and southern Iberia there are indications that the spawning season has been of longer duration in recent years for all size classes (reaching in some cases 8 months of the year for large fish). These patterns are in general agreement with existing literature and theoretical expectations of sardine spawning being driven locally by the seasonal cycle of water temperature, assuming preferences for spawning at 14 –15°C and avoidance for temperatures below 12°C and above 16°C. Regional quotient plots indicated that spawning tolerance to higher temperatures increases progressively with decreasing latitude. Despite the weak evidence for geographical differences in temperature tolerance that may have some genetic origin, the degree of spatio-temporal overlap in sardine-spawning activity within Atlantic European waters is unlikely to promote any reproductive isolation in that area.     

Models of fish school size in relation to environmental productivity

A simple energy-balance model, relating energetic requirements of fish schools to food production, was used to predict shoal sizes. Lower limits to school size are unlikely to be set by food but rather by predation. Upper limits depend on both food and school behavior, being greater for schools that break up to feed than for schools that remain continuously cohesive. Faced with a decreasing food supply, a school could either break into smaller schools or change behavior, increasing the area available for foraging. The models suggest that environmental productivity needs to be considered when examining fishery statistics such as (catch per unit effort), where maximum catch may be limited by maximum school size.     

Effects of Clear-Cut Harvesting on Boreal Ground-Beetle Assemblages (Coleoptera: Carabidae) in Western Canada

We compared pitfall catches from four types of mature lodgepole pine—white spruce forest with those from five age classes of young forest regenerating subsequent to clear-cutting. Ground beetles were most abundant in the youngest sites (1–2 years since cutting) and in the mature stands on moist soil. Species richness was higher in regenerating sites than in mature forest. Cluster analysis grouped the ground-beetle fauna according to forest age and forest type, suggesting that there is a general pattern of recovery after logging. Responses of common species to forest cutting fell into three groups: (1) forest generalists (2 species) were not dramatically affected, (2) species of open habitat (27 species) appeared and/or increased in abundance, and (3) mature forest species (10 species) disappeared or decreased in abundance. Populations of many mature forest species appear to recover following logging, but several specialists did not recolonize even the oldest regenerating stands. Furthermore, fragmentation and creation of large areas of relatively homogeneous young forest stages through logging may have detrimental long-term effects even on the more abundant forest generalists. We must better understand subtle variations in habitat in order to maintain invertebrate diversity while harvesting the boreal forest.     

The evolution of non-maternal caretaking among anthropoid primates: do helpers help?

Non-maternal infant care among nonhuman primates has frequently been investigated from the perspective of the caretaker. Here we examine whether allocaretaking behavior provides direct reproductive benefits to mothers. Comparative analyses that control for the effects of allometry and phylogeny reveal that allocaretaking behavior correlates with relatively fast infant growth and reproduction, but is not associated with the production of large infants. These results are consistent with those from studies of other taxa; primate helpers appear to increase the reproductive success of female breeders. In addition, our findings contrast with those derived from traditional allometric analyses and underscore the importance of controlling for the potentially confounding effects of phylogeny in comparative analyses. Received: 28 May 1996 / Accepted after revision: 16 November 1996     

Dispersal per recruit: an efficient method for assessing sustainability in marine reserve networks.

Marine reserves are an increasingly important tool for the management of marine ecosystems around the world. However, the effects of proposed marine reserve configurations on sustainability and yield of populations are typically not estimated because of the computational intensity of direct simulation and uncertainty in larval dispersal and density-dependent recruitment. Here we develop a method for efficiently assessing a marine reserve configuration for persistence and yield of a population with sedentary adults and dispersing larvae. The method extends the familiar sustainability criteria of individual replacement for single populations based on eggs-per-recruit (EPR) to spatially distributed populations with sedentary adults, a dispersing larval phase, and limited carrying capacity in the settlement-recruit relationship. We refer to this approach as dispersal-per-recruit (DPR). In some cases, a single DPR calculation, based on the assumption that post-settlement habitat is saturated (i.e., at maximum recruitment), is sufficient to determine population persistence, while in other cases further iterative calculations are required. These additional calculations reach an equilibrium more rapidly than a full simulation of age- or size-structured populations. From the DPR result, fishery yield can be computed from yield-per-recruit (YPR) at each point. We assess the utility of DPR calculations by applying them to single reserves, uniformly distributed systems of reserves, and randomly sized and spaced systems of reserves on a linear coastline. We find that for low levels of EPR in fished areas (e.g., 10% or less of the natural, unfished EPR when post-settlement habitats are saturated by 35% of natural settlement), a single DPR calculation is sufficient to determine persistence of the population. We also show that, in uniform systems of reserves with finite reserve size, maximal fisheries yield occurs when the density of reserves is such that all post-settlement habitat is nearly saturated with settlers. Finally, we demonstrate the application of this approach to a realistic proposed marine reserve configuration.     

A study of the genetic relationships within and among wolf packs using DNA fingerprinting and mitochondrial DNA

Summary DNA fingerprinting and mitochondrial DNA analyses have not been used in combination to study relatedness in natural populations. We present an approach that involves defining the mean fingerprint similarities among individuals thought to be unrelated because they have different mtDNA genotypes. Two classes of related individuals are identified by their distance in standard errors above this mean value. The number of standard errors is determined by analysis of the association between fingerprint similarity and relatedness in a population with a known genealogy. We apply this approach to gray wolf packs from Minnesota, Alaska, and the Northwest Territories. Our results show that: (1) wolf packs consist primarily of individuals that are closely related genetically, but some packs contain unrelated, non-reproducing individuals; (2) dispersal among packs within the same area is common; and (3) short-range dispersal appears more common for female than male wolves. The first two of these genetically-based observations are consistent with behavioral data on pack structure and dispersal in wolves, while the apparent sex bias in dispersal was not expected.USA Offprint requests to: N. Lehman at the present address     

It's a dirty job but someone has to do it: The role of marine benthic macrofauna in organic matter turnover and nutrient recycling to the water column

Benthic macrofaunal populations through their feeding, bioturbation, burrow construction and sediment irrigation activities have profound influences on organic matter inputs to marine sediments (biodeposition) and on the vertical distribution of deposited organic matter within the sediment. These effects in turn influence the rates and pathways of organic matter mineralisation, and element cycles. Similarly, bioturbation, burrow construction and burrow irrigation are major determinants of sediment-water column fluxes of oxygen and nutrients.

In this review, I discuss the influences of the different benthic macrofaunal feeding (functional) groups on mineralisation processes and sediment-water column fluxes of particulate and dissolved nutrients. How these effects influence diagenic processes, the balance between aerobic and anaerobic processes, and the redox status of the surficial sediments. Finally, I discuss some of the limitations of the predominantly laboratory techniques which have been used to study “macrofaunal effects” and how this hinders the inclusion of the effects in quantitative sediment biogeochemical models.     

Seasonal variation of total dissolved arsenic and arsenic speciation in a polluted surface waterway

Seasonal differences in the dissolved arsenic concentration and speciation in a contaminated urban waterway in northwest England have been determined using a coupled ion chromatography-inductively coupled plasma-mass spectrometry (IC-ICP-MS) technique. Waters sampled in the vicinity of an industrial works during relatively dry conditions in April 2000 were found to contain total arsenic concentrations (As) of up to 132 g L^–1, more than an order magnitude greater than the 4 g L^–1 maximum found in December 2000. The difference in As between the April and December sampling periods is speculated to be largely due to the irregular anthropogenic supply of arsenic to the watercourse. For both sampling periods, the dissolved arsenic was exclusively inorganic in nature and had an As(V)/As ratio of between 0.6 and 0.8. Analysis of samples taken downstream of the industrial site, after the confluence with a relatively As-poor stream, revealed that As(III), As(V) and As concentrations were lower than would be expected from conservative mixing. The As(V)/As ratio was also observed to decrease markedly. The loss of arsenic from solution is thought to be due to adsorption on the iron oxyhydroxide-rich sediment observed to coat the riverbed downstream of the confluence. The reduction in the As(V)/As ratio is believed to be due to the more rapid adsorption of As(V) compared to that of As(III). Deviations from conservative behaviour were more marked during the relatively dry April 2000 sampling period and suggest the increased importance of adsorption processes controlling arsenic availability during this time.     

Worker piping in honey bees (<Emphasis Type="Italic">Apis mellifera</Emphasis>): the behavior of piping nectar foragers

This study investigates the brief piping signals ("stop signals") of honey bee workers by exploring the context in which worker piping occurs and the identity and behavior of piping workers. Piping was stimulated reliably by promoting a colony's nectar foraging activity, demonstrating a causal connection between worker piping and nectar foraging. Comparison of the behavior of piping versus non-piping nectar foragers revealed many differences, e.g., piping nectar foragers spent more time in the hive, started to dance earlier, spent more time dancing, and spent less time on the dance floor. Most piping signals (approximately 99%) were produced by tremble dancers, yet not all (approximately 48%) tremble dancers piped, suggesting that the short piping signal and the tremble dance have related, but not identical, functions in the nectar foraging communication system. Our observations of the location and behavior of piping tremble dancers suggest that the brief piping signal may (1) retard recruitment to a low-quality food source, and (2) help to enhance the recruitment success of the tremble dance.