Lineage diversification in a widespread species: roles for niche divergence and conservatism in the common kingsnake, Lampropeltis getula

Niche conservatism and niche divergence are both important ecological mechanisms associated with promoting allopatric speciation across geographical barriers. However, the potential for variable responses in widely distributed organisms has not been fully investigated. For allopatric sister lineages, three patterns for the interaction of ecological niche preference and geographical barriers are possible: (i) niche conservatism at a physical barrier; (ii) niche divergence at a physical barrier; and (iii) niche divergence in the absence of a physical barrier. We test for the presence of these patterns in a transcontinentally distributed snake species, the common kingsnake ( Lampropeltis getula ), to determine the relative frequency of niche conservatism or divergence in a single species complex inhabiting multiple distinct ecoregions. We infer the phylogeographic structure of the kingsnake using a range-wide data set sampled for the mitochondrial gene cytochrome b . We use coalescent simulation methods to test for the presence of structured lineage formation vs. fragmentation of a widespread ancestor. Finally, we use statistical techniques for creating and evaluating ecological niche models to test for conservatism of ecological niche preferences. Significant geographical structure is present in the kingsnake, for which coalescent tests indicate structured population division. Surprisingly, we find evidence for all three patterns of conservatism and divergence. This suggests that ecological niche preferences may be labile on recent phylogenetic timescales, and that lineage formation in widespread species can result from an interaction between inertial tendencies of niche conservatism and natural selection on populations in ecologically divergent habitats.     

Modelled spatial distribution of marine fish and projected modifications in the North Atlantic Ocean

The objectives of this work were to examine the past, current and potential influence of global climate change on the spatial distribution of some commercially exploited fish and to evaluate a recently proposed new ecological niche model (ENM) called nonparametric probabilistic ecological niche model (NPPEN). This new technique is based on a modified version of the test called Multiple Response Permutation Procedure (MRPP) using the generalized Mahalanobis distance. The technique was applied in the extratropical regions of the North Atlantic Ocean on eight commercially exploited fish species using three environmental parameters (sea surface temperature, bathymetry and sea surface salinity). The numerical procedure and the model allowed a better characterization of the niche (sensu Hutchinson) and an improved modelling of the spatial distribution of the species. Furthermore, the technique appeared to be robust to incomplete or bimodal training sets. Despite some potential limitations related to the choice of the climatic scenarios (A2 and B2), the type of physical model (ECHAM 4) and the absence of consideration of biotic interactions, modelled changes in species distribution explained some current observed shifts in dominance that occurred in the North Atlantic sector, and particularly in the North Sea. Although projected changes suggest a poleward movement of species, our results indicate that some species may not be able to track their climatic envelope and that climate change may have a prominent influence on fish distribution during this century. The phenomenon is likely to trigger locally major changes in the dominance of species with likely implications for socio‐economical systems. In this way, ENMs might provide a new management tool against which changes in the resource might be better anticipated.     

Phylogeographic and demographic effects of Pleistocene climatic fluctuations in a montane salamander, Plethodon fourchensis

Climatic changes associated with Pleistocene glacial cycles profoundly affected species distributions, patterns of interpopulation gene flow, and demography. In species restricted to montane habitats, ranges may expand and contract along an elevational gradients in response to environmental fluctuations and create high levels of genetic variation among populations on different mountains. The salamander Plethodon fourchensis is restricted to high-elevation, mesic forest on five montane isolates in the Ouachita Mountains. We used DNA sequence data along with ecological niche modelling and coalescent simulations to test several hypotheses related to the effects of Pleistocene climatic fluctuations on species in montane habitats. Our results revealed that P. fourchensis is composed of four well-supported, geographically structured lineages. Geographic breaks between lineages occurred in the vicinity of major valleys and a narrow high-elevation pass. Ecological niche modelling predicted that environmental conditions in valleys separating most mountains are suitable; however, interglacial periods like the present are predicted to be times of range expansion in P. fourchensis . Divergence dating and coalescent simulations indicated that lineage diversification occurred during the Middle Pleistocene via the fragmentation of a wide-ranging ancestor. Bayesian skyline plots showed gradual decreases in population size in three of four lineages over the most recent glacial period and a slight to moderate amount of population growth during the Holocene. Our results not only demonstrate that climatic changes during the Pleistocene had profound effects on species restricted to montane habitats, but comparison of our results for P. fourchensis with its parapatric, sister taxon, P. ouachitae , also emphasizes how responses can vary substantially even among closely related, similarly distributed taxa.     

Habitat mapping,population size and preventing extinction through improving the conservation status of Calamus nambariensis Becc. - an endemic and threatened cane of Assam,India

Cane is one of the important forest products after timber, form an integral part of a rural and tribal population of many of the tropical countries of South East Asia, Africa and America. Calamus nambariensis Becc. has been recognized as endemic and threatened cane to the North East region of India. The plant is restricted to only two pockets of Assam with a poor population size. Therefore, conservation of this plant through proper scientific investigation is utmost necessary. The present investigation has as its objectives to study the distribution, estimation of population size, standardization of suitable micropropagation methods for reintroduction and reinforcement in suitable wild habitat as determined by ecological niche modelling (ENM) for the purposes of conservation. For improving the conservation status of the species, potential area and habitat for reintroduction was determined using maximum entropy (MaxEnt) distribution modelling algorithm. The population size in both the site was found to be very poor i.e., mean density, frequency of occurrence and abundance in relation to other associated species was 0.600, 29.26 and 2.307 in Nambor Reserve Forest whereas 0.526, 27.407 and 2.112 respectively in Gibbon Wildlife Sanctuary. Macropropagation of C. nambariensis was standardized here through seed germination which was found to be more efficient in terms of time and cost which revealed 87% germination in treated seeds, followed by 61% only for untreated seeds till 90 days. It was also observed that seedlings in the hilly slope of Gibbon Wildlife Sanctuary (reinforcement) showed high survivability than that of the hilly slop of Lahorijan Reserve Forest (reintroduction). Further, survival rate was measured for 24 months, which revealed significantly very high on an average of 97.85% in both the locations, while 1200 numbers of C. nambariensis plantlets were transferred to the field. The present study could change the population size of C. nambariensis in its natural habitat, proving effective means for preventing extinction and improving conservation status of the plant.