Restoring Western (Basalt) Plains grassland. 2. Field emergence, establishment and recruitment following direct seeding

Summary   Both reservation of small remnants and ecological restoration of degraded areas will be crucial if the Victorian Western (Basalt) Plains grassland community is to be conserved in the long term. This study examined the potential of direct seeding as a technique for grassland restoration by recording the initial establishment and subsequent recruitment success of 64 (predominantly perennial) grassland species direct sown onto a constructed site. Forty-three (67%) of the sown species emerged and established during the 2-year study and a further three species were recorded in subsequent years. In the second year, 32 species increased their number either through seedling or vegetative recruitment and 30 species dispersed beyond their original sown plot. Seed size was not correlated with field emergence but life form did influence initial field success for some groups. The finding that many species are able to establish and recruit under the study conditions supports the need for further investigation of direct seeding in the restoration of grassland communities.     

Extinction risk assessment for the species survival plan (SSP®) population of the Bali mynah (Leucopsar rothschildi)

The Bali mynah Species Survival Plan (SSP^®), an Association of Zoos and Aquariums program, strives to maintain the genetic and demographic health of its population, avoid unplanned changes in size, and minimize the risk of population extinction. The SSP population meets current demographic and genetic objectives with a population size of 209 birds at 61 institutions and 96% genetic diversity (GD) retained from the source population. However, participating institutions have expressed concerns regarding space allocation, target population size (TPS), breeding restrictions, inbreeding depression, and harvest in relation to future population availability and viability. Based on these factors, we assess five questions with a quantitative risk assessment, specifically a population viability analysis (PVA) using ZooRisk software. Using an individual-based stochastic model, we project potential population changes under different conditions (e.g. changes in TPS and genetic management) to identify the most effective management actions. Our projections indicate that under current management conditions, population decline and extinction are unlikely and that although GD will decline over 100 years the projected loss does not exceed levels acceptable to population managers (less than 90% GD retained). Model simulations indicate that the combination of two genetic management strategies (i.e. priority breeding based on mean kinship and inbreeding avoidance) benefits the retention of GD and reduces the accumulation of inbreeding. The current TPS (250) is greater than necessary to minimize the risk of extinction for the SSP population but any reduction in TPS must be accompanied by continued application of genetic management. If carefully planned, birds can be harvested for transfer to Bali for a reintroduction program without jeopardizing the SSP population. Zoo Biol 28:230–252, 2009. © 2009 Wiley-Liss, Inc.     

Conservation corridors affect the fixation of novel alleles

Corridors are a popular tool for conservation of small populations. However, two purported benefits of corridors, increasing gene flow and providing a means for the recolonization of extinct patches of habitat (population rescue), may have unappreciated impacts on the likelihood that a new allele will become incorporated (fixed) within a population. Using a simulation model, I demonstrate that connecting a stable, isolated population with a population that requires periodic rescue (due to extinction via natural or anthropogenic disturbance) can affect fixation of alleles in the stable population, largely by changing the effective population size Ne of the two-patch complex. When disturbance is rare, connecting the two patches with corridors can increase fixation of beneficial alleles and increase loss of harmful alleles. However, the opposite occurs when rates of disturbance are high: corridors can promote fixation of harmful alleles and reduce fixation of beneficial alleles. Because the impact of corridors hinges upon disturbance frequency (i.e. rate of population rescue), population growth rate, movement rates, and habitat quality, different species are likely to have different responses to corridor-mediated fixation, even if the species reside within the same ecological community. By changing fixation, corridors could thus either promote adaptation or extinction.     

Demography of the demosponge Amphimedon compressa: Evaluation of the importance of sexual versus asexual recruitment to its population dynamics

We used size-based population matrix models to describe the demography of the demosponge Amphimedon compressa. The relative importance of growth, survivorship, and recruitment to population growth (λ) was assessed by performing elasticity and life table response experiment (LTRE) analyses. We also evaluated the relative contribution of sexual and asexual recruitment to λ by analyzing four different scenarios: (1) the combined impact of sexual and asexual recruitment, (2) the impact of only sexual recruits, (3) the impact of only asexual fragmentation, and (4) the impact of no recruitment. Size-based transition matrices were parameterized with field data collected at two sites in the southwest coast of Puerto Rico: Media Luna West (MLW), a reef exposed to high water movement and at Las Pelotas (LP), a reef experiencing low water motion. Estimated λ of 0.8940 and 0.7973 at MLW and LP respectively suggest that both populations are declining. Elasticity analysis indicated that survivorship may be the most important contributor to λ at both sites. However, λ at MLW was influenced more by the survivorship of small individuals whereas survivorship of the large size-class contributed the most to λ at LP. LTRE analysis indicates that the difference in λ between sites was mostly due to difference in survivorship of small sponges. At both sites, λ decreased considerably when sexual recruitment was excluded from the model whereas the absence of asexual recruitment barely changed λ. Therefore, it is suggested that sexual recruitment plays a major role (in comparison to asexual fragmentation) in the population dynamics of this sponge at the studied sites. We conclude that spatial variability in water motion plays an important role in population dynamics of A. compressa by influencing survivorship patterns, including the relative contribution of asexual and sexual recruitment to population growth.