Impacts of climate warming and habitat loss on extinctions at species' low-latitude range boundaries

Polewards expansions of species' distributions have been attributed to climate warming, but evidence for climate‐driven local extinctions at warm (low latitude/elevation) boundaries is equivocal. We surveyed the four species of butterflies that reach their southern limits in Britain. We visited 421 sites where the species had been recorded previously to determine whether recent extinctions were primarily due to climate or habitat changes. Coenonympha tullia had become extinct at 52% of study sites and all losses were associated with habitat degradation. Aricia artaxerxes was extinct from 50% of sites, with approximately one‐third to half of extinctions associated with climate‐related factors and the remainder with habitat loss. For Erebia aethiops (extinct from 24% of sites), approximately a quarter of the extinctions were associated with habitat and three‐quarters with climate. For Erebia epiphron, extinctions (37% of sites) were attributed mainly to climate with almost no habitat effects. For the three species affected by climate, range boundaries retracted 70–100 km northwards (A. artaxerxes, E. aethiops) and 130–150 m uphill (E. epiphron) in the sample of sites analysed. These shifts are consistent with estimated latitudinal and elevational temperature shifts of 88 km northwards and 98 m uphill over the 19‐year study period. These results suggest that the southern/warm range margins of some species are as sensitive to climate change as are northern/cool margins. Our data indicate that climate warming has been of comparable importance to habitat loss in driving local extinctions of northern species over the past few decades; future climate warming is likely to jeopardize the long‐term survival of many northern and mountain species.     

A carboniferous chondrichthyan assemblage from residues within a Triassic karst system at Cromhall quarry,Gloucestershire, England

Abstract. Sixteen different Lower Carboniferous (Tournaisian Courceyan to Chadian age, Mississippian) chondrichthyan teeth types have been extracted from Triassic erosional/aeolian fills in shallow karst systems found in the limestone quarry at Cromhall, Gloucestershire, England. These Carboniferous teeth have been found within a much larger assemblage of disarticulated bones and teeth belonging to small late Triassic terrestrial reptiles, for which Cromhall quarry is famous. The Carboniferous teeth are derived fossils, released during subaerial dissolution of the surrounding limestones. Owing to low specimen numbers and uncertainty of intraspecific character, 10 types of teeth are left in open nomenclature, although it is likely they represent new taxa. They belong to Jalodus, Ctenacanthiformes, Protacrodus, Orodus, Chomatodus, Petalodontidae, Euchondrocephali?, Helodus and Psephodus. A new genus and species, Cromhallia parvunda, of indeterminate phylogenetic relationships, is also erected. The assemblage includes also an identified suite comprising Thrinacodus ferox, Bransonella cf. nebraskensis and Stethacanthus cf. altonensis. The identification of all fish teeth found in the Cromhall assemblages as derived fossils from the Carboniferous removes any ambiguity regarding the fully terrestrial nature of the late Triassic fauna preserved in the residue‐bearing karst systems.     

Convergent evolutionary processes driven by foraging opportunity in two sympatric morph pairs of Arctic charr with contrasting post‐glacial origins

The expression of two or more discrete phenotypes amongst individuals within a species (morphs) provides multiple modes upon which selection can act semi‐independently, and thus may be an important stage in speciation. In the present study, we compared two sympatric morph systems aiming to address hypotheses related to their evolutionary origin. Arctic charr in sympatry in Loch Tay, Scotland, exhibit one of two discrete, alternative body size phenotypes at maturity (large or small body size). Arctic charr in Loch Awe segregate into two temporally segregated spawning groups (breeding in either spring or autumn). Mitochondrial DNA restriction fragment length polymorphism analysis showed that the morph pairs in both lakes comprise separate gene pools, although segregation of the Loch Awe morphs is more subtle than that of Loch Tay. We conclude that the Loch Awe morphs diverged in situ (within the lake), whereas Loch Tay morphs most likely arose through multiple invasions by different ancestral groups that segregated before post‐glacial invasion (i.e. in allopatry). Both morph pairs showed clear trophic segregation between planktonic and benthic resources (measured by stable isotope analysis) but this was significantly less distinct in Loch Tay than in Loch Awe. By contrast, both inter‐morph morphological and life‐history differences were more subtle in Loch Awe than in Loch Tay. The strong ecological but relatively weak morphological and life‐history divergence of the in situ derived morphs compared to morphs with allopatric origins indicates a strong link between early ecological and subsequent genetic divergence of sympatric origin emerging species pairs. The emergence of parallel specialisms despite distinct genetic origins of these morph pairs suggests that the effect of available foraging opportunities may be at least as important as genetic origin in structuring sympatric divergence in post‐glacial fishes with high levels of phenotypic plasticity. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

Long‐term impacts of invasive species on a native top predator in a large lake system

1. Declining abundances of forage fish and the introduction and establishment of non‐indigenous species have the potential to substantially alter resource and habitat exploitation by top predators in large lakes. 2. We measured stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) in field‐collected and archived samples of Lake Ontario lake trout (Salvelinus namaycush) and five species of prey fish and compared current trophic relationships of this top predator with historical samples. 3. Relationships between δ¹⁵N and lake trout age were temporally consistent throughout Lake Ontario and confirmed the role of lake trout as a top predator in this food web. However, δ¹³C values for age classes of lake trout collected in 2008 ranged from 1.0 to 3.9‰ higher than those reported for the population sampled in 1992. 4. Isotope mixing models predicted that these changes in resource assimilation were owing to the replacement of rainbow smelt (Osmerus mordax) by round goby (Neogobius melanostomus) in lake trout diet and increased reliance on carbon resources derived from nearshore production. This contrasts with the historical situation in Lake Ontario where δ¹³C values of the lake trout population were dominated by a reliance on offshore carbon production. 5. These results indicate a reduced capacity of the Lake Ontario offshore food web to support the energetic requirements of lake trout and that this top predator has become increasingly reliant on prey resources that are derived from nearshore carbon pathways.     

A meta‐analysis of latitudinal variations in life‐history traits of roach,Rutilus rutilus,over its geographical range: linear or non‐linear relationships?

1. We collated information from the literature on life history traits of the roach (a generalist freshwater fish), and analysed variation in absolute fecundity, von Bertalanffy parameters, and reproductive lifespan in relation to latitude, using both linear and non-linear regression models. We hypothesized that because most life history traits are dependent on growth rate, and growth rate is non-linearly related with temperature, it was likely that when analysed over the whole distribution range of roach, variation in key life history traits would show non-linear patterns with latitude.
2. As fecundity depends strongly on length, and the length structure of females varied among populations, latitudinal patterns in fecundity were examined based on residuals from the length–fecundity relationship. The reproductive lifespan of roach was estimated as the difference between age at maturity and maximum age of females in each population.
3. The three life history traits of roach analysed all varied among populations and were non-linearly related to latitude. Only the relationship between reproductive lifespan and latitude was a better fit to a linear that to a quadratic model, although Loess smoothing curves revealed that this relationship was actually closer to biphasic than linear in form. A latitude of 50°N formed a break point in all three life history traits.
4. The negative relationships we have described between (i) fecundity and reproductive lifespan and (ii) fecundity and egg mass suggest that lower fecundity is compensated for by longer lifespan, while lower fecundity is compensated for by an increased egg mass, when analysed independently of location.     

Cheilostomatous Bryozoa from Vanuatu

The present account of some Bryozoa from Vanuatu is the first study of reef-flat species from the eastern Coral Sea. Based on samples collected from several shallow water localities on the island of Efate, a total of 92 species is described, including a new family, three new genera and 20 new species. Some of the newly recognized species are the result of taxonomic revision stimulated by these new samples, while others are entirely new to science. Of the new taxa described here, 16 are presently known only from Vanuatu. The total number of species recorded does not accurately represent the true taxonomic diversity of the Cheilostomatida of Vanuatu, and further sampling, at other localities and in other habitats, is needed before it can be reasonably estimated. The fauna is predominantly Indo-West Pacific in character with a high proportion of species apparently known only in the Southwest Pacific.