Interspecific competition between mice: A reciprocal field manipulation experiment

Previous studies have demonstrated a species replacement sequence in disturbed forest and heathland, with the native New Holland mouse (Pseudomys novaehollandiae) replacing the introduced house mouse (Mus musculus) in the earliest part of the succession. The replacement appeared to be competitive displacement and this has been confirmed by controlled experimental removal of P. novaehollandiae from field sites, which produced significant increases in the abundance and habitat use of Mus musculus. This paper reports the results of the controlled reciprocal manipulation experiment in the field. A pulsed addition of M. musculus to three treatment plots produced significant reductions in the abundance and habitat use of P. novaehollandiae, when compared with control plots with no addition of M. musculus. This effect was observed only at high M. musculus densities, and the return to the control conditions within 3 months of the pulsed addition is consistent with asymmetric interspecific competition from competitively superior P. novaehollandiae. The importance of considering the regional abundance of M. musculus in relation to its competitive ability is stressed, as at high densities M. musculus is able to create its own ecological space contrary to its more usual competitively submissive status.     

DEVONIAN CONODONT APPARATUSES AND THEIR VICARIOUS SKELETAL ELEMENTS

Recognition of four types of skeletal apparatuses of Devonian compound and platform conodonts, which conform in their basic plan to those already established in the Ordovician, Silurian, and Carboniferous, emphasizes the persistence of but a few structural types in the Paleozoic. The vicarious nature primarily of compound but also of platform elements in different multielement associations demonstrates mosaic evolution in Devonian apparatuses and has far-reaching taxonomic implications. Homologies of skeletal elements, for which a system of symbols is introduced, are evident in different apparatus types and show that the relationships of elements have been obscured by the older form taxonomy. Multielement analysis revises the taxonomic scope of the common Devonian genera, Icriodus, Polygnathus , and Ozarkodina. As a consequence of apparatus reconstruction, four new genera are proposed: Parapolygnathus, Cryptotaxis, Delotaxis , and Pedavis.     

Leaf traits of congeneric host plants explain differences in performance of a specialist herbivore

1. Within the host range of herbivorous insects, performance hierarchies are often correlated with relatedness to a primary host plant, as plant traits are phylogenetically conserved. Therefore, it was hypothesised that differences in herbivore performance on closely related plant species are due to resistance traits that vary in magnitude, rather than in the nature of the traits. 2. This hypothesis was tested by manipulating putative resistance traits of three congeneric thistle species (Cirsium arvense, Cirsium palustre, and Cirsium vulgare) and assessing the performance of the oligophagous, leaf‐feeding beetle, Cassida rubiginosa. Measurements were done of survival, weight gain, and development time of the beetle on its primary host, C. arvense, and two alternative hosts under low and high nutrient availability, and on shaved and unshaved leaves. 3. Survival of C. rubiginosa was strongly dependent on plant species with final mean survival rates of 47%, 16%, and 8% on C. arvense, C. palustre, and C. vulgare, respectively. Survival was primarily explained by leaf trichome densities, and to a lesser extent by specific leaf area. Leaf flavonoid concentrations did not explain differences in beetle survival, and there were no differences in beetle weight gain or development time of individuals that survived to adulthood. 4. No beetles survived on unshaved (hairy) C. vulgare plants, but manipulating leaf trichome densities of the thistle species by shaving the leaves moderated the plant‐specific resistance, and equalised the survival rates. Survival of C. rubiginosa on alternative congeneric hosts was explained by a common physical resistance trait that varied in magnitude.     

Evidence for divergence and adaptive isolation in post‐glacially derived bimodal allopatric and sympatric rainbow smelt populations

The roles of ecological speciation and reinforcement in the formation of contemporary diversity remain contentious. In the present study, we contrast phenotypic and molecular divergence within morphologically diverged bimodal sympatric and allopatric pairs of rainbow smelt, Osmerus mordax. We hypothesize that, in sympatry, evidence of selection associated with resource partitioning will be visible through strong divergence, reinforcement, and greater character displacement. Parallel morphological divergence was observed between the two trophic forms (macrophagous and microphagous), with several examples of greater trait divergence in sympatry than allopatry. Mitochondrial DNA sequence analysis indicated no association between historical clades and morphology; however, Bayesian clustering using microsatellites supported the isolation of these morphs under both allopatry and sympatry. Estimates of genetic isolation were one order of magnitude lower than measures of morphological divergence, consistent with a hypothesis of strong contemporary selection. Using experimental crosses, we obtained similar rates of fertilization success among the allopatric hybrid and pure crosses; whereas, in the sympatric hybrid crosses, fertilization rates dropped by 30–50%, suggesting a clear role for reinforcement through prezygotic incompatibilities. The present study supports the hypothesis that processes of post‐glacial radiation and diversification differ between sympatry and allopatry, and indicates a role for reinforcement and ecological processes in recent sympatric diversification. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 583–594.     

Foraging behaviour and ecology of the Cape pangolin (Manis temminckii) in north‐western Zimbabwe

An ethogram was developed for the foraging Cape pangolin in order to construct activity budgets. Behaviour was classified into seven categories and nine types of feeding sites were recorded. Activity budgets of animals foraging in different vegetation types are presented to illustrate the importance of vegetation on behaviour patterns and feeding site utilization. Availability of feeding sites may depend on the vegetation type with trees, shrubs and woody debris comprising most feeding sites. Seven prey species were recorded. One animal displayed strictly diurnal activity which suggests greater variability in activity patterns than previously thought.     

The distribution and biology of Lonchopteridae (Diptera) in upland regions of northern England

Abstract. 1. A survey was made of the distribution of Lonchopteridae over 2 years at forty sites in northern England. Material was collected by pitfall trapping.
2. Two species, Lonchoptera lutea and L.furcata , were taken in approximately similar numbers. No other species were recorded.
3. Considerable separation of the two species was found, with both species occurring at ten sites, whilst one species only was taken at twenty-five sites. L.furcata occurred coinrnonly on upland mineral sods, shallow peat soils and on lowland bogs whilst L.lutea was numerically most abundant on upland blanket bog.
4. Almost 39% of the L.lutea specimens and 14% of the L.furcata captures were males.
5. The capture of numbers of males of L.furcata is unusual, since the species is regarded as being parthenogenetic and males occur only in a very small part of the species' range. Confirmation of the association between the males and females of L.furcata is given, whilst there is close agreement between the cliaetotaxy of British males and females, and British and continental European females. The suggestion that the males belong to an undescribed species is rejected.
6. The seasonal capture of L.lutea adults is similar at all altitudes. Captures of males of L.furcata show an abrupt seasonal change above and below about 420 m; captures being in mid-summer in the higher altitude zone and between October and December at lower altitudes. The captures of females of L.furcata show the same trend, but this is partially obscured by the longer life-span of the females. It is suggested that this difference represents a change in the lifecycle, possibly from an annual to a biannual one at the higher altitudes.
7. The biology and distribution of the Lonchopteridae at low altitudes requires investigation.     

Estimating Carrying Capacity for Sea Otters in British Columbia

ABSTRACT We estimated carrying capacity for sea otters (Enhydra lutris) in the coastal waters of British Columbia, Canada, by characterizing habitat according to the complexity of nearshore intertidal and sub-tidal contours. We modeled the total area of complex habitat on the west coast of Vancouver Island by first calculating the complexity of the Checleset Bay-Kyuquot Sound (CB-KS) region, where sea otters have been at equilibrium since the mid-1990s. We then identified similarly complex areas on the west coast of Vancouver Island (WCVI model), and adapted the model to identify areas of similar complexity along the entire British Columbia coast (BC model). Using survey data from the CB-KS region, we calculated otter densities for the habitat predicted by the 2 models. The density estimates for CB-KS were 3.93 otters/km² and 2.53 otters/km² for the WCVI and BC models, respectively, and the resulting 2 estimates of west coast of Vancouver Island complex habitat carrying capacity were not significantly different (WCVI model: 5,123, 95% CI = 3,337–7,104; BC model: 4,883, 95% CI = 3,223–6,832). The BC model identified the region presently occupied by otters on the central British Columbia coast, but the amount of coast-wide habitat it predicted (5,862 km²) was relatively small, and the associated carrying capacity estimate (14,831, 95% CI = 9,790–20,751) was low compared to historical accounts. We suggest that our model captured a type of high-quality or optimum habitat prevalent on the west coast of Vancouver Island, typified by the CB-KS region, and that suitable sea otter habitat elsewhere on the coast must include other habitat characteristics. We therefore calculated a linear, coast-wide carrying capacity of 52,459 sea otters (95% CI = 34,264–73,489)—a more realistic upper limit to sea otters in British Columbia. Our carrying capacity estimates are helping set population recovery targets for sea otters in Canada, and our habitat predictions represent a first step in Critical Habitat identification. This habitat-based approach to estimating carrying capacity is likely suitable for other nonmigratory, density-dependent species.     

Thermal niche, large-scale movements and implications of climate change for a critically endangered marine vertebrate

Climate change is expected to have a number of impacts on biological communities including range extensions and contractions. Recent analyses of multidecadal data sets have shown such monotonic shifts in the distribution of plankton communities and various fish species, both groups for which there is a large amount of historical data on distribution. However, establishing the implications of climate change for the range of endangered species is problematic as historic data are often lacking. We therefore used a different approach to predict the implications of climate change for the range of the critically endangered planktivourous leatherback turtle (Dermochelys coriacea). We used long‐term satellite telemetry to define the habitat utilization of this species. We show that the northerly distribution limit of this species can essentially be encapsulated by the position of the 15°C isotherm and that the summer position of this isotherm has moved north by 330 km in the North Atlantic in the last 17 years. Consequently, conservation measures will need to operate over ever‐widening areas to accommodate this range extension.