Evidence of character displacement in microhabitat use between two tropical sympatric Holcosus lizard species (Reptilia, Teiidae)

Interspecific competition between sympatric related species leading to character displacement is critical for species coexistence, especially in tropical habitats. We examined microhabitat use of two sympatric species of tropical lizards of the genus Holcosus in relationship to the microhabitats available in two ecosystems. The species H. festivus lives exclusively in the forest and uses microhabitats in proportion to their availability; while the other, H. quadrilineatus, lives both in forest and on the beach and selects microhabitats with specific characteristics. In the ecosystem where these two lizards live in sympatry (forest), we observed a differential microhabitat use between the two species. However, these differences indicated changes in habitat use by H. quadrilineatus (the smaller species) concerning its patterns of habitat selection in the ecosystem (beach) where only this species occurs. The age of the lizards did not affect the patterns of selection of microhabitats of either species. Shifts in microhabitat use may allow coexistence in sympatry of both species, which might result from the competitive exclusion of the smaller species by the larger species. Key words: Interspecific competition, Holcosus, Lizards, Microhabitat use, Tropical habitats

Potential Distribution Shifts of Plant Species under Climate Change in Changbai Mountains, China

Shifts in alpine tundra plant species have important consequences for biodiversity and ecosystem services. However, recent research on upward species shifts have focused mainly on polar and high-latitude regions and it therefore remains unclear whether such vegetation change trends also are applicable to the alpine tundra at the southern edges of alpine tundra species distribution. This study evaluated an alpine tundra region within the Changbai Mountains, China, that is part of the southernmost alpine tundra in eastern Eurasia. We investigated plant species shifts in alpine tundra within the Changbai Mountains over the last three decades (1984–2015) by comparing contemporary survey results with historical ones and evaluated potential changes in the distribution of dwarf shrub and herbaceous species over the next three decades (2016–2045) using a combination of observations and simulations. The results of this study revealed that the encroachment of herbaceous plants had altered tundra vegetation to a significant extent over the last three decades, especially within low and middle alpine tundra regions in Changbai Mountains, China. The herbaceous species would continue shifting upward and expanding while their dwarf shrub counterparts would continue shifting upward and shrinking over the next three decades under the RCP 4.5 and RCP 8.5 scenarios. The upward shifts of plant species would not keep up with the rate of climate warming under the RCP 8.5 scenarios. The dominant plant tundra species may transform from dwarf shrubs to herbaceous varieties. The results of this study provide a scientific basis for biodiversity protection under climate change and a reference data set for additional research on alpine vegetation dynamics.

Self-replacement after small-scale partial crown dieback in austral Nothofagus dombeyi forests affected by an extreme drought

The spectrum of structural response in drought-induced mortality (degree of partial crown mortality) could play a key role in pervasive changes in plant composition, as individual openings could reset self-replacement dynamics or trigger shifts in vegetation. Here we capture the community pattern 17 years after a drought episode over a range of canopy responses in Nothofagus dombeyi forests. We applied a widespread demographic approach to address evidence of species shifts vs. self-replacement and to relate partial dieback to understory structure and composition. Assuming that the outcome of growth release of the understory components can be observed 17 years after canopy loss, this study reveals evidence of self-replacement in N. dombeyi forests heavily affected by drought. Alternatively, when the co-dominant species A. chilensis is widely present in the understory and large gaps are opened, a compositional shift may be possible, with a potential change in forest functionality. Individual partial openings do not favor more shrubby communities or a shift toward a new community. Thus, partial crown dieback contributes to self-replacement mechanisms by hampering strong growth release in understory shrubs, as evident in plots with high mortality, and by facilitating the growth of dominant tree species.

Network reorganization and breakdown of an ant–plant protection mutualism with elevation

Both the abiotic environment and the composition of animal and plant communities change with elevation. For mutualistic species, these changes are expected to result in altered partner availability, and shifts in context-dependent benefits for partners. To test these predictions, we assessed the network structure of terrestrial ant-plant mutualists and how the benefits to plants of ant inhabitation changed with elevation in tropical forest in Papua New Guinea. At higher elevations, ant-plants were rarer, species richness of both ants and plants decreased, and the average ant or plant species interacted with fewer partners. However, networks became increasingly connected and less specialized, more than could be accounted for by reductions in ant-plant abundance. On the most common ant-plant, ants recruited less and spent less time attacking a surrogate herbivore at higher elevations, and herbivory damage increased. These changes were driven by turnover of ant species rather than by within-species shifts in protective behaviour. We speculate that reduced partner availability at higher elevations results in less specialized networks, while lower temperatures mean that even for ant-inhabited plants, benefits are reduced. Under increased abiotic stress, mutualistic networks can break down, owing to a combination of lower population sizes, and a reduction in context-dependent mutualistic benefits.