Rodent Communities in an Exurbanizing Southwestern Landscape (U.S.A.)

Abstract:  Ranches are being converted to exurban housing developments in the southwestern United States, with potentially significant but little-studied impacts on biological diversity. We captured rodents on 48 traplines in grasslands, mesquite savannas, and oak savannas in southeastern Arizona that were grazed by livestock, embedded in exurban housing developments, grazed and embedded in development, or neither grazed nor embedded in development. Independent of habitat or development, rodent species richness, mean rank abundance, and capture rates of all rodents combined were negatively related to presence of livestock grazing or to its effects on vegetative ground cover. Exurban development had no obvious effects on rodent variety or abundance. Results suggest southwestern exurban developments can sustain a rich assemblage of grassland and savanna rodents if housing densities are low and houses are embedded in a matrix of natural vegetation with little grazing.     

Assessing the Potential to Restore Historic Grazing Ecosystems with Tortoise Ecological Replacements

The extinction of large herbivores, often keystone species, can dramatically modify plant communities and impose key biotic thresholds that may prevent an ecosystem returning to its previous state and threaten native biodiversity. A potentially innovative, yet controversial, landscape‐based long‐term restoration approach is to replace missing plant‐herbivore interactions with non‐native herbivores. Aldabran giant (Aldabrachelys gigantea) and Madagascan radiated (Astrochelys radiata) tortoises, taxonomically and functionally similar to the extinct Mauritian giant tortoises (Cylindraspis spp.), were introduced to Round Island, Mauritius, in 2007 to control the non‐native plants that were threatening persistence of native species. We monitored the response of the plant community to tortoise grazing for 11 months in enclosures before the tortoises were released and, compared the cost of using tortoises as weeders with the cost of using manual labor. At the end of this period, plant biomass; vegetation height and cover; and adult, seedling, flower, and seed abundance were 3–136 times greater in adjacent control plots than in the tortoise enclosures. After their release, the free‐roaming tortoises grazed on most non‐native plants and significantly reduced vegetation cover, height, and seed production, reflecting findings from the enclosure study. The tortoises generally did not eat native species, although they consumed those native species that increased in abundance following the eradication of mammalian herbivores. Our results suggest that introduced non‐native tortoises are a more cost‐effective approach to control non‐native vegetation than manual weeding. Numerous long‐term outcomes (e.g., change in species composition and soil seed bank) are possible following tortoise releases. Monitoring and adaptive management are needed to ensure that the replacement herbivores promote the recovery of native plants. Estudiando el Potencial para Restaurar Ecosistemas Históricos de Forrajeo con Reemplazos Ecológicos de Tortugas Terrestres     

Managing Invasive Aquatic Plants in a Changing System: Strategic Consideration of Ecosystem Services

Abstract:  Climate change is projected to increase stress for many coastal plant communities. Along large portions of the North American coast, habitat degradation from anthropogenic changes to the environment already threaten the community structure of tidal marshes and submerged aquatic grass beds. The potential loss of ecological services historically provided by these communities has been a long-standing rationale for aggressive control of invading plants such as Phragmites australis and Hydrilla verticillata . Increasing evidence of ecological services provided by invasive species such as P. australis and H. verticillata suggest that, in the face of increasing stress, it may be prudent to take a more pragmatic approach regarding the effect of these species on coastal ecosystems. The notable resilience of these species to control efforts and their competitive success and comparative vigor in stressed systems and capacity to provide at least some beneficial services combine to suggest some invasive species may have a useful role in managed coastal ecosystems.     

Inbreeding and Loss of Genetic Variation in a Reintroduced Population of Mauritius Kestrel

Abstract:  Many populations have recovered from severe bottlenecks either naturally or through intensive conservation management. In the past, however, few conservation programs have monitored the genetic health of recovering populations. We conducted a conservation genetic assessment of a small, reintroduced population of Mauritius Kestrel ( Falco punctatus ) to determine whether genetic deterioration has occurred since its reintroduction. We used pedigree analysis that partially accounted for individuals of unknown origin to document that (1) inbreeding occurred frequently (2.6% increase per generation; N _eI= 18.9), (2) 25% of breeding pairs were composed of either closely or moderately related individuals, (3) genetic diversity has been lost from the population (1.6% loss per generation; N _eV= 32.1) less rapidly than the corresponding increase in inbreeding, and (4) ignoring the contribution of unknown individuals to a pedigree will bias the metrics derived from that pedigree, ultimately obscuring the prevailing genetic dynamics. The rates of inbreeding and loss of genetic variation in the subpopulation of Mauritius Kestrel we examined were extreme and among the highest yet documented in a wild vertebrate population. Thus, genetic deterioration may affect this population's long-term viability. Remedial conservation strategies are needed to reduce the impact of inbreeding and loss of genetic variation in this species. We suggest that schemes to monitor genetic variation after reintroduction should be an integral component of endangered species recovery programs.     

A Comparison of Decentralized Minigrids and Dispersed Diesels for Irrigation Pumping in Sahelian Africa

A key ingredient in the expansion of agricultural output in many developing countries is the availability of reliable and cost-effective energy supplies for irrigation. Such supplies are also fundamental to any strategy to stimulate rural economic development. This paper compares the costs of water pumping through the use of commonly-used, small diesel-driven pumpsets versus a decentralized generator connected to a small electrified grid. An example representative of irrigated cropping systems found in the Senegal River Basin is used to compare costs. The results show that pumping costs from a decentralized power supply and minigrid are roughly comparable with those of direct-drive diesel pumpsets. Further, excess capacity would be available to provide power for small industries and other rural needs. In many sparsely populated rural locations where low capacity factors make central grid extension uneconomic, a minigrid with a guaranteed load of irrigation pumping can be an attractive alternative for providing power for rural development.     

Evaluating the Potential for Conservation Development: Biophysical, Economic, and Institutional Perspectives

Abstract:  The widespread conversion of rural land to low-density residential development poses an immediate threat to biodiversity and to the provision of ecosystem services. Given that development will continue and environmental stakes are high, analyzing alternative growth strategies is critical. Conservation development is one such strategy that has the potential to benefit ecosystems and diverse stakeholders including developers, homebuyers, governments, and society as a whole. Conservation development clusters homes on one part of a property to manage the most ecologically important land for the conservation of biodiversity and ecosystem services. We draw on lessons learned from landscape ecology, open-space development, and regional planning to weigh the biophysical, economic, and institutional evidence for and against conservation development. Conservation development offers many potential environmental and economic advantages: relatively high home values and appreciation rates, lower development costs, and social and ecological benefits to society including landscape connectivity, protection and active stewardship of important ecological assets, and the maintenance of ecosystem services. But this approach also has shortcomings: it may require enlightened institutional regulations and regional planning (and/or ecologically aware developers), it is not always more profitable than conventional development and thus may require subsidies or incentives, and additional research is required to fully understand its benefits and drawbacks. With more information on the effects of clustering, the development of flexible zoning laws, and effective regional planning, conservation development could be a viable strategy for sustaining biodiversity and ecosystem services in changing landscapes.