The One-Migrant-per-Generation Rule in Conservation and Management

In the face of continuing habitat fragmentation and isolation, the optimal level of connectivity between populations has become a central issue in conservation biology. A common rule of thumb holds that one migrant per generation into a subpopulation is sufficient to minimize the loss of polymorphism and heterozygosity within subpopulations while allowing for divergence in allele frequencies among subpopulations. The one-migrant-per-generation rule is based on numerous simplifying assumptions that may not hold in natural populations. We examine the conceptual and theoretical basis of the rule and consider both genetic and nongenetic factors that influence the desired level of connectivity among subpopulations. We conclude that one migrant per generation is a desirable minimum, but it may be inadequate for many natural populations. We suggest that a minimum of 1 and a maximum of 10 migrants per generation would be an appropriate general rule of thumb for genetic purposes, bearing in mind that factors other than genetics may further influence the ideal level of connectivity.     

Sexual selection and spring arrival times of red-necked and Wilson's phalaropes

Summary Seasonal changes in sex ratios during a 4-year study of red-necked phalaropes and a 3-year study of Wilson's phalaropes showed that females preceded males to breeding and/or courtship areas. The degree to which females preceded males may have been constrained by harsh weather, as the arrival of red-necked phalaropes was synchronous in 1983, when spring was unusually late. Neither sex defended territories; females competed vigorously for direct access to males. These findings show that selection for sexually asynchronous arrival need not act through territoriality. We interpret early female arrival as an adaptation for obtaining mates and coclude that sexual selection may be an important determinant of arrival times in mate defense social systems.     

Temporal variability in winter travel patterns of Yellowstone bison: the effects of road grooming.

The influence of winter recreation on wildlife in Yellowstone National Park (YNP), Wyoming and Montana, USA, is a controversial issue. In particular, the effects of road grooming, done to facilitate snowmobile and snowcoach travel, on bison (Bison bison) ecology are under debate. We collected data during winters, from 1997 to 2005, on bison road use, off-road travel, and activity budgets to quantify temporal trends in the amount of bison road and off-road travel and to identify the ecological factors affecting bison movements and use of the groomed road system in the Madison-Gibbon-Firehole (MGF) area of YNP. Using model comparison techniques, we found bison travel patterns to be influenced by multiple, interacting effects. Road travel was negatively correlated with road grooming, and we found no evidence that bison preferentially used groomed roads during winter. Snow water equivalent, bison density, and the springtime melt period were positively correlated with both bison road and off-road travel. From behavioral scans on 68,791 bison, we found that travel is only a small percentage (11%) of all bison activity, with foraging comprising 67% of observations. Also, only 7% of traveling bison and 30% of foraging bison were displacing snow, and we suggest foraging, rather than traveling, is likely the major energetic cost to bison in winter. Bison utilize their own trail network, connecting foraging areas using stream corridors, geothermal pathways, and self-groomed travel routes. Our results indicate that temporal patterns in bison road travel are a manifestation of general travel behavior and that groomed roads in the MGF do not appear to be a major factor influencing bison ecology and spatial redistribution. We suggest that the changes in bison spatial dynamics during the past three decades have likely been the result of the natural phenomenon of density-dependent range expansion, rather than having been caused by the anthropogenic influence of road grooming.     

Toward a high-rate enhanced biological phosphorus removal process in a membrane-assisted bioreactor.

A membrane enhanced biological phosphorus removal (MEBPR) process was studied to determine the impact of hydraulic retention time (HRT) and solids retention time (SRT) on the removal of chemical oxygen demand (COD), nitrogen, and phosphorus from municipal wastewater. The MEBPR process was capable of delivering complete nitrification independent of the prevailing operating conditions, whereas a significant improvement in COD removal efficiency was observed at longer SRTs. In the absence of carbon-limiting conditions, the MEBPR process was able to achieve low phosphorus concentrations in the effluent at increasingly higher hydraulic loads, with the lowest HRT being 5 hours. The MEBPR process was also able to maintain optimal phosphorus removal when the SRT was increased from 12 to 20 days. However, at higher suspended solids concentrations, a substantial increase was observed in carbon utilization per unit mass of phosphorus removed from the influent. These results offer critical insights to the application of membrane technology for biological nutrient removal systems.     

A closer look at detectability

Environmental and Ecological Statistics - The theory underlying line transect and variable circular plot surveys—distance sampling—begins with an assumed detectability function, giving...     

Reclamation techniques in southwestern wyoming

Bridger Coal Company operates a 5.8 million tpy surface coal mine thrity five miles northeast of Rock Springs. Wyoming. Approximately 20.000 acres are under permit, with disturbance over the life of the mine projected to reach 10,000 acres. Located on the western rim of the continental divide, the mine receives less than 8.5 inches of precipitation annually. Soils in the area are coarse-textured. and problems associated with elevated salinity and sodicity arc encountered. A variety of common reclamation techniques have been modified to reflect these conditions. Soil horizons are segregated during salvage operations (the surface six inches as topsoil and the balance as subsoil). Unsuitable materials are not salvaged. Direct application of soil is used (over 130 acres in 1983) to maximize native plant regeneration and conserve soil fertility. Inter-seeding of seeding failures has proven to be significantly more successful than chisel plowing and reseeding. Broadcast seeding has been ineffective because of strong winds, and a no till drill has been modified to handle diverse seed mixes and rock conditions. The utility of fertilization under typically xeric moisture regimes is being evaluated. A research project has been initiated to assess establishment of a predominately native, diverse seed mix under irrigation, as well as to determine irrigation rates and duration.     

Conditional and unconditional estimators of population size

Estimators for the population sizes of animal species are similar to Horvitz-Thompson estimators — they involve dividing counts of detected animals by the probabilities of detection. Knowing detection probabilities for different subpopulations allows one to estimate each sub-population size with such an estimator, and to add the results for an estimator of the total population. In the case where the proportions of animals belonging to the different sub-populations are also known, this paper shows that using those proportions to arrive at a common average detection probability will, when used in conjunction with the total number of animals detected, result in a better estimator. We provide two examples where the inferior estimator may seem sensible.     

Mating system and mating success of the desert spider Agelenopsis aperta

Field studies of the desert spider Agelenopsis aperta revealed a primarily monogamous mating system. However polygyny, polyandry and polygynandry were superimposed upon the primary system, with 9% of the marked males and 11% of the marked females in a field population mating more than once. In the laboratory males commonly mated multiply with fertile offspring resulting, while females were less likely than males to mate multiply. Monogamy under field conditions was enforced by two factors: (1) high travel costs to males, and (2) a significant decline in female receptivity after the first mating. Heavy males were more likely to be accepted by females both in the field, and in female choice experiments conducted in the laboratory. Finally, male weight determined the outcome of male-male agonistic interactions over females. One possible explanation for female choice in this system which lacks male parental investment is that females may be using male size as an indicator of future success of their offspring.     

Motivation and vector navigation in honey bees

Animals that forage from a central place can keep track of their displacement relative to home through a process called "path integration." During a study of the stability of homing information over time, we noticed that honey bees held at a feeding place for several hours sometimes headed not in the homeward compass direction on their release, but in the reverse compass direction. This behavior suggested that the path integration system had been reset to a state corresponding to an outward flight to the food. Most models of insect navigation assume that it is the experience of reaching home that resets the path integration system, enabling the activation of vectors appropriate for subsequent outbound foraging trips. Here we provide evidence that this resetting can be influenced by motivational cues associated with food deprivation. The effect of food deprivation is independent of any positional cues provided by familiar landmarks or by experience in traveling toward a goal.     

Local and Indigenous management of climate change risks to archaeological sites

Hundreds of thousands of significant archaeological and cultural heritage sites (cultural sites) along the coasts of every continent are threatened by sea level rise, and many will be destroyed. This wealth of artefacts and monuments testifies to human history, cosmology and identity. While cultural sites are especially important to local and Indigenous communities, a stall in coordinated global action means adaptation at a local scale is often unsupported. In response, this paper produces a practical climate change risk analysis methodology designed for independent, community-scale management of cultural sites. It builds on existing methods that prioritise sites most at risk from climate impacts, proposing a field survey that integrates an assessment of the relative cultural value of sites with assessment of exposure and sensitivity to climate impacts. The field survey also stands as a monitoring program and complements an assessment of organisational adaptive capacity. The preliminary field survey was tested by Indigenous land managers in remote northern Australia at midden and rock art sites threatened by sea level rise, extreme flood events and a range of non-climactic hazards. A participatory action research methodology—incorporating planning workshops, semi-structured interviews and participant observations—gave rise to significant modifications to the preliminary field survey as well as management prioritisation of 120 sites. The field survey is anticipated to have global application, particularly among marginalised and remote Indigenous communities. Well-planned and informed participation, with community control, monitoring and well-informed actions, will contribute significantly to coordinated global and regional adaptation strategies.