Unconnected Patches Research Articles

Connectivity and homogenisation of population sizes: an experimental approach in Lacerta vivipara

Summary At regional scales, dispersal is known to prevent metapopulation extinction by buffering stochastic processes. Theory predicts that connectivity, through density‐dependent dispersal rates, should spatially homogenize population density and synchronize local population dynamics in the long term. However, empirical evidence for the effect of connectivity on synchrony and local population dynamics remains scarce. We experimentally manipulated connectivity in order to investigate the homogenisation effect on population size. The experimental design consisted of 16 patches of common lizard populations (Lacerta vivipara), half of which were connected by dispersal. The design allowed us to identify candidates for dispersal in unconnected patches. We found that population sizes became spatially more and more homogeneous with time in connected patches, whereas extinctions or demographic explosions were observed in unconnected patches. Juvenile dispersal was density‐dependent in connected patches but not in unconnected ones. These results suggest that the loss of connection modifies population functioning by influencing how dispersal is determined by local conditions. Finally, population explosions in unconnected patches were followed by a sharp decrease in population size. So non‐extinct, unconnected populations did not stabilize. This could be due to over‐compensatory density dependence. Population viability analysis models suggest that environmental stochasticity and catastrophic events, in addition to the density‐dependent process, are required to explain population size variation and extinction.

SPATIAL ECOLOGY OF PREDATOR–PREY INTERACTIONS: CORRIDORS AND PATCH SHAPE INFLUENCE SEED PREDATION

Corridors that connect patches of disjunct habitat may be promising tools for mediating the negative impacts of habitat fragmentation, but little is known about how corridors affect ecological interactions. In eight 12-ha experimental landscapes, we examined how corridors affect the impact of invertebrate, rodent, and avian seed predators on pokeweed, Phytolacca americana. Over 13 months in 2000 and 2001, we quantified the effects of patch shape, connectivity, and predator type on the number of seeds germinating in the field (germinants), seed removal, and the viability of remaining seeds. Corridors did not affect the number of P. americana germinants in experimental exclosures or the viability of seeds remaining in exclosures. However, corridors affected the removal of seeds in a predator-specific manner: invertebrates removed more seeds in unconnected patches, whereas rodents removed more seeds in connected patches. Seed removal by birds was similar in connected and unconnected patches. Total seed removal by all seed predators was not affected by corridors, because invertebrates removed more seeds where rodents removed fewer seeds, and vice versa. Overall, seed predation significantly reduced the number and viability of remaining seeds, and reduced the number of germinants in 2000 but not in 2001. The abundance of naturally occurring P. americana plants in our experimental patches in 2000 decreased with increasing seed removal from exclosures but was not related to viability or germinants in 2000, suggesting that seed removal may shape the distribution and abundance of this species. Complementary patterns of seed removal by rodents and invertebrates suggest that corridors alter the effects of these predator taxa by changing the relative amounts of edge and core (nonedge) habitats in a patch. Because invertebrates and rodents do not completely overlap in the seeds they consume, corridors may change predation pressure on seeds that are primarily consumed by one predator type, with potential consequences for the composition of plant and seed predator communities.

CORRIDOR USE BY DIVERSE TAXA

One of the most popular approaches for maintaining populations and con- serving biodiversity in fragmented landscapes is to retain or create corridors that connect otherwise isolated habitat patches. Working in large-scale, experimental landscapes in which open-habitat patches and corridors were created by harvesting pine forest, we showed that corridors direct movements of different types of species, including butterflies, small mam- mals, and bird-dispersed plants, causing higher movement between connected than between unconnected patches. Corridors directed the movement of all 10 species studied, with all corridor effect sizes .68%. However, this corridor effect was significant for five species, not significant for one species, and inconclusive for four species because of small sample sizes. Although we found no evidence that corridors increase emigration from a patch, our results show that movements of disparate taxa with broadly different life histories and functional roles are directed by corridors.

Age- and sex-specific responses of the gray-tailed vole, <i>Microtus canicaudus</i>, to connected and unconnected habitat patches

We monitored demography, movement, and reproductive behavior of gray-tailed voles, Microtus canicaudus, in experimental habitat patches with and without corridors to test the hypotheses that more individuals would move among patches in corridor than in control unconnected habitats, and that individuals would distribute themselves more evenly among patches if corridors were present than if they were not. We predicted that more males than females would move among patches in both treatments and that juveniles in control habitats would exhibit delayed sexual maturation if their dispersal was delayed and opposite-sex relatives remained in proximity to each other. All experiments were conducted in eight 0.2-ha enclosures planted with alfalfa that was fragmented into four patches (each 156 m2) separated by 12.5 m of bare ground. In four of the enclosures, patches were connected by 1 m wide habitat corridors. Corridors facilitated movements, with males moving more than females. However, corridors did not result i...

Electron emission from ferroelectric ceramics with a special design patterned front electrode

Electron emission from a ceramic disk is due to spontaneous polarization switching induced by a high-voltage pulse applied to the surface electrodes. With a conventional front electrode, emission was erratic as a function of samples and decayed with shot number. On the contrary, when the front electrode consisted of a pattern of unconnected patches contained within a ring, emission was stable. The physics of the two configurations is investigated and a possible interpretation of the two different behaviors is given.

CORRIDOR AND DISTANCE EFFECTS ON INTERPATCH MOVEMENTS: A LANDSCAPE EXPERIMENT WITH BUTTERFLIES

The hypothesis that corridors increase animal movement between habitat fragments, a central tenet of conservation biology, has been virtually untested. This study demonstrates that corridors increase interpatch movement rates of two butterfly species. The hypothesis was tested in a large-scale, replicated experiment, in which 27 equal-sized (1.64-ha) patches of early successional habitat were created within large areas of pine forest. Patches varied in whether or not they were connected to another patch by a corridor, and in their distance from other patches (64–384 m). The results of mark–release–recapture studies showed that two open-habitat butterfly species, Junonia coenia and Euptoieta claudia, moved more frequently between patches connected by corridors than between unconnected patches. Interpatch movement was significantly, negatively related to interpatch distance. Interpatch movement rates of J. coenia were significantly, positively related to the density of its host and nectar resource, Linaria canadensis. Corridor effects were stronger for males than for females and were most pronounced within three days after butterflies were marked. Pine forest was not a complete barrier to butterfly movement; both species moved between unconnected patches, even at the longest distances. However, the results of this study suggest that corridors will increase long-distance movements of habitat-restricted species.