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Weight-length relations of fishes are useful for estimation of biomass from length observations, e.g., in fisheries or conservation research. Here we provide some guidance to authors of such papers, in order to facilitate the publication and review process

Populations of mountain golden heather (Hudsonia montana), a threatened North Carolina shrub, are declining due to the suppression of natural fires and increased trampling by hikers and campers. Consequently, proposed management strategies have focused on conducting controlled burns and restricting human traffic. To help design an optimal management plan, we used demographic data from a 5-year field study of H. montana--which included a controlled burn--to construct size-based population projection matrices. Using these matrices, we projected the consequences of instituting controlled burns and hiking and camping restrictions separately and in tandem. We also determined the burn frequency that would maximize H. montana's population growth rate. Finally, we used a stochastic model to determine how environmental fluctuations could alter the efficacy of conservation measures. Our results suggest that, although neither burning nor trampling reduction alone can reverse H. montana's decline, a judicious combination of the two has an excellent chance of doing so. A burn frequency of once every 6-8 years should maximize H. montana's population growth, although the interburn interval could be increased to 12-16 years without significantly jeopardizing the success of the management plan. Our results show that, even with the limited data available, size-based projection matrix models can be useful tools for identifying promising combinations of multiple management strategies for most threatened plants.

Land managers often suggest fencing to protect rare plant species from being trampled in heavily used recreation areas, but there are few documented examples of the efficacy of this strategy. In a 7-year demographic study we examined the reproduction, survival, and long-term viability of the endangered sentry milk-vetch (Astragalus cremnophylax var. cremnophylax) before and after protection from trampling. Demographic monitoring and population viability analyses indicated that the population has fluctuated during the 7 years. Before protection the population declined: 26% of individuals died, mortality surpassed natality, and age of first reproduction was significantly older than post-protection. Fifty-eight percent of the population was severely damaged. Population viability analyses of pre-protection years predicted that the population would go extinct within 100 years. Since protection, the population stabilized, grew, and declined again. Seedlings reached reproductive maturity more quickly. Recruitment increased and peaked in 1993 coincident with abundant precipitation, but again declined in 1994. The total numbers of undamaged plants surpassed the numbers of damaged plants. Models of the post-protection population predict stability. Multiple-linear regression analysis indicated that winter and spring precipitation were significantly correlated with lambda. Both \"good\" and \"bad\" climatic conditions occurred during the pre- and post-protection periods. Because of small population size and depauperate genetic diversity, climate will continue to influence population growth. Nevertheless, models indicate that where trampling and bad climatic conditions were coupled, extinction was accelerated. Recovery of sentry milk-vetch will depend on continued protection, augmentation, and environmental factors, although risk of extinction remains very high.

In Poland Equisetum telmateia Ehrh. is a sub-mountainous species. In lowland regions it is fairly rare. A highly populated site of this species is noted near the village of Klasztorne in Western Pomerania. The investigation was carried out in the year 2006. In the investigated area giant horsetail chiefly occurs in forest phytocenoses on embankments and flood terraces of the river Kaczynka valley (Fraxino-Alnetum W.Mat. 1952, Ribeso nigri-Alnetum Sol.Górn. (1975) 1987). Very abundantly it grows in non-forest phytocenoses where on the river bank its fields are found on forest outskirts encroaching the area of a wet field (community of the Aegopodion podagrariae alliance). Horsetail shows different cover in the individual patches of phytocoenoses. However, it does not depend on the type of the phytocoenosis being directly associated with the degree of solar exposure.

Designing a reserve system for a threatened territorial species such as the Northern Spotted Owl requires the balancing of biological necessity against economic reality. The Spotted Owl conservation plan and the Pacific Northwest timber industry are in conflict because both demand large areas of mature and old-growth coniferous forest. The primary focus of this paper is the efficient design of a reserve system for territorial species with obligate juvenile dispersal. We examine the relationship between the degree of aggregation of suitable owl habitat, the level of occupancy of that habitat by pairs of Spotted Owls, and the likelihood of owl persistence given different amounts and spatial arrangements of suitable habitat across the landscape. We develop a population model for Spotted Owls that includes an abstracted forest landscape where suitable owl habitat is arrayed in clusters embedded in a matrix not suitable for owl habitation. We conclude from our study of this model that, for any given fraction of the landscape set aside in reserves, the level of occupancy (efficiency of use) of that area will increase as the aggregation of suitable habitat increases. After the reserves reach a size that includes territories for 20 to 25 owl pairs, however, there are diminishing returns from further increases. Preserving connectivity and increasing the geographical extent of the reserve begin to outweigh increased size in importance in insuring the long-term viability of the species.

Risk assessment to determine the probability of persistence of populations has an increasingly important role in the development of conservation and resource use strategies. We used the computer program VORTEX to estimate the viability of populations of Leadbeater's possum, Gymnobelideus leadbeateri, an endangered species of forest-dependent marsupial inhabiting timber production areas in southeastern Australia. The study simulated population dynamics and genetic variability in metapopulations occupying small numbers of habitat patches of varying size. The impacts of different rates of migration between subpopulations were also examined. Computer simulations with subpopulations of 20 or fewer G. leadbeateri were characterized by very rapid rates of extinction, and most metapopulations typically failed to persist for longer than 50 yr. Increasing either the rate of migration or the number of small subpopulations exacerbated the demographic instability of metapopulations when subpopulations contained <20 individuals and when migration rates were kept within plausible values for dispersal of this species between disjunct habitat patches. This was reflected by lower rates of population growth and depressed probabilities of metapopulation persistence. These effects appeared to be associated with substantial impacts of demographic stochasticity on very small subpopulations together with dispersal of animals into either empty patches or functionally extinct (i.e., single-sex) subpopulations. There were significant differences between metapopulation dynamics of 40 animals and those comprising 20 or fewer individuals. Increased migration and addition of subpopulations of 40 G. leadbeateri resulted in higher rates of population growth, lower probabilities of extinction, and longer persistence times. Extinctions in these scenarios were also more likely to be reversed through recolonization by dispersing individuals. At the highest rates of migration, subpopulations of 40 G. leadbeateri were essentially panmictic and behaved genetically as a single larger population. Increased numbers of subpopulations and accelerated rates of migration slowed the loss of expected heterozygosity in all scenarios. However, there was a significant (>10%) loss in expected heterozygosity over 100 yr even at the highest rates of migration among five subpopulations of 40 animals. Our analyses predicted that while demographic stability might occur in metapopulations of 200 G. leadbeateri, considerably more individuals than this might be required to avoid a significant decline in genetic variability over 100 yr. Thus, genetic and demographic stability in G. leadbeateri occurred at different metapopulation sizes. Metapopulation structures used in our investigation were hypothetical. However, our results might emulate the dynamics of some populations of arboreal marsupials over the next century within substantial areas of wood production forests in the Central Highlands of Victoria. In many of these areas, there are now only a few and typically very small remaining patches of old-growth forest that will provide suitable habitat for G. leadbeateri in the long term. Thus, over the next 100 yr, the species might be lost from extensive parts of its present range within montane ash forests that are utilized for timber production. Our study also indicated that there might be metapopulation structures in which the addition of subpopulations and moderate migration could have a negative effect on subpopulation persistence. These findings highlight the importance of understanding the size, number, and isolation of subpopulations that are targeted for management.

The US Fish and Wildlife Service uses a database that lists a speciesas endangered or threatened under the provisions of the Endangered Species Act. However, the database lacks biological data that could be used by officials to determine the vulnerability of species.

In 1990, in response to requests from the private sector, the U.S. Fish and Wildlife Service circulated draft guidelines to protect Northern Spotted Owls (Strix occidentalis caurina) from harm due to harvest of old-growth trees in proximity to nests or activity centers. The guidelines are often referred to as the \"40% guideline,\" the \"500-acre guideline,\" and the \"70-acre guideline.\" I comment on the rationales used to develop the guidelines and suggest ways the guidelines could be improved.