Contrasting home-range size and spatial partitioning in cryptic and sympatric pipistrelle bats

The extent of spatial partitioning in insectivorous bats, whose prey is patchily distributed and transient in nature, remains a contentious issue. The recent separation of a common Palaearctic bat, the pipistrelle, into Pipistrellus pipistrellus and Pipistrellus pygmaeus, which are morphologically similar and sympatric, provides an opportunity to examine this question. The present study used radio telemetry to address the spatial distribution and foraging characteristics of P. pipistrellus and P. pygmaeus in northeast Scotland, to test the hypothesis that coexistence between these species is facilitated through spatial segregation. We reveal large and significant differences in the spatial distribution and foraging characteristics of these two cryptic species. Individual P. pipistrellus home ranges were on average three times as large as that of P. pygmaeus, and they foraged for approximately an hour longer each night. Inter-specific spatial overlap was minimal (<5%) and core foraging areas of either species were essentially mutually exclusive despite the proximity of the two roosts. Inter-specific differences in range size were associated with the spatial dispersion of productive foraging sites within individual foraging ranges. P. pipistrellus foraging sites were highly dispersed, necessitating larger ranges. It is predicted that the spatial segregation revealed by the present study is a result of selection favouring the avoidance of competition in these species through differential habitat use.     

Phylogenetics of American scallops (Bivalvia: Pectinidae) based on partial 16S and 12S ribosomal RNA gene sequences

Pectinids constitute one of the most conspicuous groups of marine bivalves, and include some of the most important species from the point of view of fisheries and aquaculture. In spite of this, their systematics and evolution are not well understood. Only two molecular phylogenetic analyses based on relatively wide taxonomic samplings have been published. These studies largely neglected American species, some of which are central for testing current models of pectinid evolution and diversification, or are commercially valuable. We have sequenced 820 nucleotide base pairs of the 12S and 16S ribosomal RNA genes in nine species of pectinids belonging to six genera living along American coasts. Sequences from homologous regions of 19 other species were gathered from public databases. We constructed phylogenetic maximum-parsimony and maximum-likelihood trees of this set of 28 taxa. Our phylogenetic analysis indicates that Crassadoma is polyphyletic, and cementation to the substrate as a life habit could have appeared independently in two geographic chlamydinid lineages. Nodipecten is placed in the subfamily Pectininae, and the suspected close relationship of Amusium, Euvola and Pecten within this subfamily is also supported. Zygochlamys patagonica appears in the Chlamydinae subfamily, as expected. The existence of a separate subfamily Palliolinae is suggested but not supported statistically. The position of Argopecten, Aequipecten and Flexopecten within the subfamily Pectinidae, suggested by a recent study, could not be confirmed, and we argue that it could be due to a combination of long branch attraction and incomplete sequencing.     

Integrating phenological, chemical and biotic defences in ant-plant protection mutualisms: a case study of two myrmecophyte lineages

Summary. We examined the role of plant phenology in the evolution of anti-herbivore defence in symbiotic ant-plant protection mutualisms. Phenology of the host-plant affects traits of its herbivores, including size, growth rate, development time, and gregariousness. Traits of herbivores in turn determine what traits ants must have to protect their host. Diversity in plant phenological traits could thus help explain the great ecological diversity of coevolved ant-plant mutualisms. We explored the postulated causal chain linking phenology of the plant, herbivore adaptations to phenology, and ant adaptations for protection, by comparing two myrmecophytes presenting strong contrasts in phenology. In Leonardoxa africana, a slow-growing understory tree, growth at each twig terminal is intermittent, the rapid flushing of a single leaf-bearing internode being followed by a pause of several months. In contrast, axes of Barteria nigritana, a tree of open areas, grow continuously. Analysis of the phenology (kinetics of expansion) and chemistry of leaf development (contents of chlorophylls, lignin, and nitrogen during leaf growth) showed that these two species exhibit strongly contrasting strategies. Leonardoxa exhibited a delayed greening strategy, with rapid expansion of leaves during a short period, followed by synthesis of chlorophylls and lignins only after final leaf size has been reached. In contrast, leaves of Barteria expanded more slowly, with chlorophylls and lignin gradually synthesised throughout development. Differences in the phenology of leaf development are reflected in differences in the duration of larval development, and thereby in size, of the principal lepidopteran herbivores observed on these two plants. This difference may in turn have led to different requirements for effective defence by ants. The strategy of phenological defence may thus affect the evolution of biotic defence.     

Population dynamics and growth of juveniles of the velvet swimming crab Necora puber (Decapoda: Portunidae)

Recruitment variability plays a critical role in determining local population densities of benthic organisms, but extreme vulnerability at the onset of juvenile life is a trait that is largely responsible for population survivorship trends. The aim of the present study was to determine the role of juvenile recruitment in the population structure of Necora puber. Juveniles of N. puber were collected from the lower intertidal of rocky shores of Plymouth Sound (southwest coast of the UK) and monthly size–frequency distribution were used to determine the dynamics and the growth of the population. The parameters of the von Bertalanffy growth function were estimated (K=0.281 year⁻¹; t ₀=0.043; C=0.103; and t _s=0.268) assuming a L _∞=105 mm. Growth was markedly seasonal and present results indicated a slower juvenile growth rate than described previously for N. puber. The recruitment period was extensive and was two times higher in 2001 than in 2000 at the start of the 1+ year, but levelled off at the end of the 1+ year class on three of the four shores studied. Instantaneous mortality as high as 5.1 year⁻¹(99.4% year⁻¹) was observed during the higher recruitment year. Early juvenile mortality appears to be density dependent and a demographic bottleneck appears to limit the number of juveniles on some shores.     

Importance of competition mechanisms in successive invasions by polyphagous tephritids in La Reunion

Understanding the strength and modes of interspecific interactions between introduced and resident species (native or previously introduced) is necessary to predict invasion success. We evaluated different mechanisms of interspecific competition among four species of polyphagous fruit flies (Diptera: Tephritidae) from the island of La Reunion: one endemic species, Ceratitis catoirii, and three exotic species, C. capitata, C. rosa, and Bactrocera zonata, that have successively invaded the island. Larval competition experiments, i.e., co-infestations of the same fruit, and behavioral interference experiments measuring the ability of one female to displace another from a fruit, were performed among all pairs of the four species. We observed asymmetric and hierarchical interactions among species in both larval and adult interference competition. In agreement with the hypothesis that invasion is competition-limited, the competitive hierarchy coincided with the temporal sequence of establishment on the island, i.e., each newly established species tended to be competitively dominant over previously established ones.     

Whole-system nutrient enrichment increases secondary production in a detritus-based ecosystem

Although the effects of nutrient enrichment on consumer-resource dynamics are relatively well studied in ecosystems based on living plants, little is known about the manner in which enrichment influences the dynamics and productivity of consumers and resources in detritus-based ecosystems. Because nutrients can stimulate loss of carbon at the base of detrital food webs, effects on higher consumers may be fundamentally different than what is expected for living-plant-based food webs in which nutrients typically increase basal carbon. We experimentally enriched a detritus-based headwater stream for two years to examine the effects of nutrient-induced changes at the base of the food web on higher metazoan (predominantly invertebrate) consumers. Our paired-catchment design was aimed at quantifying organic matter and invertebrate dynamics in the enriched stream and an adjacent reference stream for two years prior to enrichment and two years during enrichment. Enrichment had a strong negative effect on standing crop of leaf litter, but no apparent effect on that of fine benthic organic matter. Despite large nutrient-induced reductions in the quantity of leaf litter, invertebrate secondary production during the enrichment was the highest ever reported for headwater streams at this Long Term Ecological Research site and was 1.2-3.3 times higher than predicted based on 15 years of data from these streams. Abundance, biomass, and secondary production of invertebrate consumers increased significantly in response to enrichment, and the response was greater among taxa with larval life spans < or = 1 yr than among those with larval life spans >1 yr. Production of invertebrate predators closely tracked the increased production of their prey. The response of invertebrates was largely habitat-specific with little effect of enrichment on food webs inhabiting bedrock outcrops. Our results demonstrate that positive nutrient-induced changes to food quality likely override negative changes to food quantity for consumers during the initial years of enrichment of detritus-based stream ecosystems. Longer-term enrichment may impact consumers through eventual reductions in the quantity of detritus.     

Serengeti wildebeest migratory patterns modeled from rainfall and new vegetation growth

We used evolutionary programming to model innate migratory pathways of wildebeest in the Serengeti Mara Ecosystem, Tanzania and Kenya. Wildebeest annually move from the southern short-grass plains of the Serengeti to the northern woodlands of the Mara. We used satellite images to create 12 average monthly and 180 10-day surfaces from 1998 to 2003 of percentage rainfall and new vegetation. The surfaces were combined in five additive and three multiplicative models, with the weightings on rainfall and new vegetation from 0% to 100%. Modeled wildebeest were first assigned random migration pathways. In simulated generations, animals best able to access rainfall and vegetation were retained, and they produced offspring with similar migratory pathways. Modeling proceeded until the best pathway was stable. In a learning phase, modeling continued with the ten-day images in the objective function. The additive model, influenced 25% by rainfall and 75% by vegetation growth, yielded the best agreement, with a multi-resolution comparison to observed densities yielding 76.8% of blocks in agreement (kappa = 0.32). Agreement was best for dry season and early wet season (kappa = 0.22-0.57), and poorest for the late wet season (0.04). The model suggests that new forage growth is a dominant correlate of wildebeest migration.     

Growth inhibition in Japanese medaka (Oryzias latipes) fish exposed to tetrachloroethylene

A recent study in our laboratory has demonstrated that tetrachloroethylene (TCE) is acutely toxic to Japanese medaka (Oryzias latipes) larvae with a 96 hr-LC50 of 18 (17-19) mg/mL (Spencer et al., 2002). In the present study we hypothesize that TCE exposure induces a developmental effect in Japanese medaka. Growth and age specific sensitivity of Japanese medaka larvae were studied with four age groups (7, 14, 21 and 28 days old) to determine tetrachloroethylene effects on these parameters. The medaka larvae were exposed for 96 hours in a single concentration (10 mg/mL) of TCE. The toxic endpoints evaluated were larvae weight, length, water content and protein concentration. The study revealed that exposure of medaka larvae to this sub-acute concentration of TCE significantly reduced length and weight in the treated group. The difference in growth between control and treated groups was more obvious in age versus length, than in age versus weight. The dry weight-fresh weight ratio (dw/fw) was shown to be higher in the control group. Water content in TCE-treated medaka was higher than in the control group, and younger fry had more water content than older ones. A higher protein concentration was also observed in TCE-treated medaka compared to the control group. These results indicate that TCE has a profound effect on the growth and development of Japanese medaka larvae.     

Contrasting structure and composition of the understory in species-rich tropical rain forests

In large samples of trees > or = 1 cm dbh (more than 1 million trees and 3000 species), in six lowland tropical forests on three continents, we assigned species with >30 individuals to one of six classes of stature at maturity (SAM). We then compared the proportional representation of understory trees (1-2 cm dbh) among these classes. The understory of the three Asian sites was predominantly composed of the saplings of large-canopy trees whereas the African and American sites were more richly stocked with trees of the smaller SAM classes. Differences in class representation were related to taxonomic families that were present exclusively in one continent or another. Families found in the Asian plots but not in the American plot (e.g., Dipterocarpaceae, Fagaceae) were predominantly species of the largest SAM classes, whereas families exclusive to the American plots (e.g., Melastomataceae sensu stricto, Piperaceae, and Malvaceae [Bombacacoidea]) were predominantly species of small classes. The African plot was similar to Asia in the absence of those American families rich in understory species, while similar to America in lacking the Asian families rich in canopy species. The numerous understory species of Africa were chiefly derived from families shared with Asia and/or America. The ratio of saplings (1-2 cm dbh) to conspecific canopy trees (>40 cm dbh) was lower in American plots than in the Asian plots. Possible explanations for these differences include phenology, moisture and soil fertility regimes, phyletic constraints, and the role of early successional plants in forest development. These results demonstrate that tropical forests that appear similar in tree number, basal area, and the family taxonomy of canopy trees nonetheless differ in ecological structure in ways that may impact the ecology of pollinators, dispersers, and herbivores and might reflect fundamental differences in canopy tree regeneration.     

Carbon sequestration in California agriculture, 1980-2000.

To better understand agricultural carbon fluxes in California, USA, we estimated changes in soil carbon and woody material between 1980 and 2000 on 3.6 x 10(6) ha of farmland in California. Combining the CASA (Carnegie-Ames-Stanford Approach) model with data on harvest indices and yields, we calculated net primary production, woody production in orchard and vineyard crops, and soil carbon. Over the 21-yr period, two trends resulted in carbon sequestration. Yields increased an average of 20%, corresponding to greater plant biomass and more carbon returned to the soils. Also, orchards and vineyards increased in area from 0.7 x 10(6) ha to 1.0 x 10(6) ha, displacing field crops and sequestering woody carbon. Our model estimates that California's agriculture sequestered an average of 19 g C x m(-2) x yr(-1). Sequestration was lowest in non-rice annual cropland, which sequestered 9 g C x m(-2) x yr(-1) of soil carbon, and highest on land that switched from annual cropland to perennial cropland. Land that switched from annual crops to vineyards sequestered 68 g C x m(-2) x yr(-1), and land that switched from annual crops to orchards sequestered 85 g C x m(-2) x yr(-1). Rice fields, because of a reduction in field burning, sequestered 55 g C x m(-2) x yr(-1) in the 1990s. Over the 21 years, California's 3.6 x 10(6) ha of agricultural land sequestered 11.0 Tg C within soils and 3.5 Tg C in woody biomass, for a total of 14.5 Tg C statewide. This is equal to 0.7% of the state's total fossil fuel emissions over the same time period. If California's agriculture adopted conservation tillage, changed management of almond and walnut prunings, and used all of its orchard and vineyard waste wood in the biomass power plants in the state, California's agriculture could offset up to 1.6% of the fossil fuel emissions in the state.