Clustered or scattered? The impact of habitat quality clustering on establishment and early spread

The match between the environmental conditions of an introduction area and the preferences of an introduced species is the first prerequisite for establishment. Yet, introduction areas are usually landscapes, i.e. heterogeneous sets of habitats that are more or less favourable to the introduced species. Because individuals are able to disperse after their introduction, the quality of the habitat surrounding the introduction site is as critical to the persistence of introduced populations as the quality of the introduction site itself. Moreover, demographic mechanisms such as Allee effects or dispersal mortality can hamper dispersal and affect spread across the landscape, in interaction with the spatial distribution of favourable habitat patches. In this study, we investigate the impact of the spatial distribution of heterogeneous quality habitats on establishment and early spread. First, we simulated introductions in one‐dimensional landscapes for different dispersal rates and either dispersal mortality or Allee effects. The landscapes differed by the distribution of favourable and less favourable habitats, which were either clustered into few large aggregates of the same quality or scattered into multiple smaller ones. Second, we tested the predictions of simulations by performing experimental introductions of hymenopteran parasitoids (Trichogramma chilonis) in ‘clustered’ and ‘scattered’ microcosm landscapes. Results highlighted two impacts of the clustering of favourable habitat: by decreasing the risks of dispersal from the introduction site to unfavourable habitat early during the invasion, it increased establishment success. However, by increasing the distance between favourable habitat patches, it also hindered the subsequent spread of introduced species over larger areas.     

Modes of regeneration and adaptation to soft‐bottom substrates of the free‐living solitary scleractinian Deltocyathoides orientalis

Scleractinian corals adapt to various substrate conditions with a variety of growth morphologies and modes of life. The azooxanthellate solitary scleractinian Deltocyathoides orientalis exhibits slightly flattened, bowl‐shaped corallites. This study describes in detail the modes of skeletal regeneration after fragmentation in association with exquisitely adaptive strategies of the corals for life on soft substrates. Larger fragments of individuals retaining almost two‐thirds to five‐sixths of the original skeletal area inherit the densely dilated, lower central skeleton, so as to keep a stable life position on soft substrates and regenerate the lost parts promptly. Even highly fragmented individuals preserving less than 10% of the original skeleton still regenerate and repair. Fragmented individuals with almost one‐sixth to one‐third original skeleton actively maintain a posture with the oral disc upward using movements of remaining tentacles. Damaged and missing soft tissues are then efficiently regenerated to form a mouth and gastrovascular cavity near the new centre of the corallum. Every regenerated individual reuses skeleton and soft tissues, and is capable of burrowing before the completion of growth morphology. The mode of regeneration characteristic of D. orientalis is thus effective and adaptive for maintenance of a stable life position on soft substrates for this solitary scleractinian. As fragmentation in deeper‐water, soft‐bottom settings is likely due to predation rather than turbulence, the rapid corallum regeneration and burrowing strategy may both represent adaptive strategies for life on soft substrates and exploitation of new niches, such as an infaunal mode of life, in a predator‐rich environment.     

Linking scorpion (Arachnida: Scorpiones) assemblage with fragment restoration in the Brazilian Atlantic Forest

Habitat loss due to forest degradation can induce changes in species richness due to variation in species susceptibility to environmental stress. This is particularly important for species with highly specific microhabitats, such as scorpions that inhabit forest habitats. In this study, the richness and abundance of these arachnids were compared between an old-growth (mature) and secondary (65 years under natural restoration) forests. Seasonal influence was also evaluated by comparing diversity between dry and wet seasons. The animals were collected through nocturnal active search using UV lamps and pitfall traps in both areas (old-growth and secondary). Both environments showed similar breast heights of trees, litter depth, litter dry mass, and understory density, indicating a high level of restoration. Scorpion diversity (characterized by Tityus pusillus, T. neglectus, T. brazilae, Bothriurus asper, and Ananteris mauryi) and abundance were not influenced by the different historical usage of both areas. In contrast, the abundance of these arachnids was highly affected by rain regimes, and increased during the dry season. These results suggest that 65 years was a sufficient time period for restoration, making it possible to maintain similar scorpion assemblages in both environments.     

Habitat loss and fragmentation reduce effective gene flow by disrupting seed dispersal in a neotropical palm

Habitat loss and fragmentation often reduce gene flow and genetic diversity in plants by disrupting the movement of pollen and seed. However, direct comparisons of the contributions of pollen vs. seed dispersal to genetic variation in fragmented landscapes are lacking. To address this knowledge gap, we partitioned the genetic diversity contributed by male gametes from pollen sources and female gametes from seed sources within established seedlings of the palm Oenocarpus bataua in forest fragments and continuous forest in northwest Ecuador. This approach allowed us to quantify the separate contributions of each of these two dispersal processes to genetic variation. Compared to continuous forest, fragments had stronger spatial genetic structure, especially among female gametes, and reduced effective population sizes. We found that within and among fragments, allelic diversity was lower and genetic structure higher for female gametes than for male gametes. Moreover, female gametic allelic diversity in fragments decreased with decreasing surrounding forest cover, while male gametic allelic diversity did not. These results indicate that limited seed dispersal within and among fragments restricts genetic diversity and strengthens genetic structure in this system. Although pollen movement may also be impacted by habitat loss and fragmentation, it nonetheless serves to promote gene flow and diversity within and among fragments. Pollen and seed dispersal play distinctive roles in determining patterns of genetic variation in fragmented landscapes, and maintaining the integrity of both dispersal processes will be critical to managing and conserving genetic variation in the face of continuing habitat loss and fragmentation in tropical landscapes.     

Association of DNA with the nuclear lamina in Ehrlich ascites tumor cells

We have studied in vitro binding of DNA to nuclear lamina structures isolated from Ehrlich ascites tumor cells. At low ionic strength in the presence of Mg++, they bind considerable amounts of mouse and bacterial DNA, forming complexes stable in 2 M NaCl. Single-stranded DNA and pulse-labeled DNA show higher binding efficiencies than native uniformly labeled DNA. When mixing occurs in 2 M NaCl, complex formation is inhibited. When nuclei are digested with DNAse I under conditions that favor chromatin condensation, DNA associated with matrices subsequently prepared from such nuclei is markedly enriched in satellite DNA. If digestion is carried out with DNAse II while nuclei are decondensed in EDTA, no enrichment in satellite DNA is observed. Preparations of purified, high-molecular weight, double-stranded DNA contain variable amounts of fast-sedimenting aggregates, which are insoluble in 2 M NaCl but are dispersed by DNA fragmentation or denaturation. These results point at some artifacts inherent in studies of DNA bound to residual nuclear structures in vivo and suggest conditions expected to avoid these artifacts. Further, using controlled digestion with DNAse II, we have studied the in vivo association of DNA with nuclear lamina isolated from Ehrlich ascites tumor cells. In the course of DNA fragmentation from above 50 kbp to about 20 kbp average size, the following events were observed. The DNA of high molecular weight (much longer than 50 kbp) behaved as if tightly bound to the nuclear lamina, as judged by sedimentation in sucrose and metrizamide density gradients, electron microscopy, and retention on glass fiber filters. As the size of DNA decreased, it was progressively detached from the nuclear lamina, and at about 20 kbp average length practically all DNA was released. The last 1-4% of DNA, although cosedimenting with the nuclear lamina in sucrose gradients, behaved as free DNA, banding at 1.14 g/cm3 in metrizamide density gradients and showing less than 4% retention on filters. At no stage of digestion did the DNA cosedimenting with nuclear lamina show changes in satellite DNA content relative to that of total DNA or enrichment in newly replicated DNA. It was shown, however, that digestion of nuclear lamina-DNA complex with EcoRI or Hae III led to the formation of DNA-protein aggregates, which banded at 1.35 g/cm3 in high salt containing metrizamide density gradients and which were strongly enriched in satellite DNA.(ABSTRACT TRUNCATED AT 400 WORDS)     

Forest fragmentation and avian nest predation in forested landscapes

Summary The size of forest fragments, the use of land bordering fragments, and the distance of nests from an edge all affect the frequency of predation upon bird nests in Maine (USA), an area where the forest has been fragmented by roads, but not significantly reduced in area. We placed artificial nests containing quail eggs in forests of different sizes and at various distances from the edge to test which of these factors was most important in describing predation. Predation was greatest in small tracts surrounded completely by land. Large areas and those bordered on at least one side by a large water body had lower predation rates. This suggests that influx of predators from nearby habitats may be responsible for much of the nest predation in forest fragments.     

Can wing morphology inform conservation priorities for Southeast Asian cave bats?

Adaptations for foraging in the complex airspaces of forest interiors may make bat species in the Asian tropics particularly susceptible to forest loss. However, ecomorphological analysis of Vietnamese bat assemblages challenges the hypothesis that, due to their greater vagility, cave‐roosting bats are less vulnerable to habitat fragmentation than foliage‐roosting species. Of the 13 most highly adapted forest‐interior species in our study, eight were cave‐roosting members of the Rhinolophidae and Hipposideridae and had wing morphologies closely resembling five foliage‐roosting members of the Murininae and Kerivoulinae—species typically thought to have low vagility. Overall, both cave‐roosting and foliage‐roosting bats exhibited a wide range of flight indices and species' wing designs corresponded with preferred foraging habitats, suggesting that foraging strategy may outweigh roost preference as a determinant of bat wing morphology and flight performance. Consequently, where such variation occurs, cave‐roosting bat ensembles are likely to include species with low vagility and similar sensitivity to habitat fragmentation. This could have important conservation implications as Asian karst formations support high cave densities and important bat diversity yet increasingly represent forest refugia in anthropogenic landscapes. We, therefore, advocate greater consideration of species vagility in determining conservation priorities for the region's bat fauna.