Climatic factors and population demography in big-eared woodrat, Neotoma macrotis

Changes in temperature and rainfall patterns can have marked impacts on small mammal populations that inhabit environments with highly fluctuating water availability. With projected increases in droughts and fewer but more intense rainfall events in the Southwestern United States, the persistence of many wildlife populations may be threatened. Our goal was to assess how temperature and rainfall during distinct dry and wet seasons influenced the dynamics of a population of big-eared woodrats (Neotoma macrotis) in a mixed oak woodland of coastal central California. We applied Pradel’s temporal symmetry models to our 21-year biannual capture–mark–recapture data set (1993–2014) to determine the effects of climatic factors on the woodrats’ apparent survival (Φ) and recruitment rate (f). Monthly Φ averaged 0.945 ± 0.001 and varied with season. Monthly f was 0.064 ± 0.001 in the wet season (f was fixed to 0 in the dry season). Monthly population growth rate (λ) varied from 0.996 ± 0.001 during the dry season to 1.001 ± 0.001 during the wet season, which indicated a stable population (0.999 ± 0.001). Total rainfall from the previous season and mean temperature during the same season positively influenced Φ and f. By contrast, Φ and f were negatively influenced by mean temperature from the previous season and total rainfall in the same season. The resulting λ fluctuated with total rainfall, particularly in the wet season. Our results suggest that the big-eared woodrat population may not be substantially affected by warm temperatures per se, potentially because of the microclimate provided by its stick houses. We also discuss its adaptability to local food resources and relatively slow life history relative to other cricetids, and propose that the big-eared woodrat population may be equipped to cope with future climate change.

Population recovery of a common vole population (Microtus arvalis) after population collapse

BACKGROUND

Population collapses in small mammals occur naturally after natural disasters and during multi-annual population fluctuations as well as after man-made intervention such as rodent management action. Although there has been extensive previous work on patterns and mechanisms of population fluctuations and cyclicity, little is known about population recovery after collapse. In Europe, the common vole (Microtus arvalis) is the major pest species in agriculture, damaging crops, competing with livestock and potentially posing a health risk to people. In this study, we investigated population recovery, recovery mechanism and recovery time of common vole populations after artificially inducing a collapse through rodenticide application.

RESULTS

The rodenticide treatment reduced abundance in spring (by about 90%) but not in summer. Demographic data (age, sex-ratio, breeding activity) suggest that it was mostly immigration and not reproduction that led to population recovery after collapse.

CONCLUSIONS

The findings indicate that rodenticide treatment should be conducted in spring before the main reproductive season starts. The treatment effect was transient and lasted for about 3 months before immigration offset the initial reduction in population abundance. This indicates that immigration patterns should be considered by managing vole populations at an appropriate spatial scale and frequency to prevent rapid repopulation. © 2018 Society of Chemical Industry.

Recovery of small rodent populations after population collapse

In this review we summarise published knowledge regarding small mammal population recovery following sudden population collapse, regardless as to whether the collapse is caused by natural or man-made events. We determine recovery mechanisms, recovery time and recovery rate, and suggest how to adapt and optimise current methods to regulate small mammal population size, for pest management and/or conservation. It is vital that the principles underlying the recovery mechanisms are known for both pest control and conservation to align management methods to either maintain animal numbers at a permanent minimum level or increase population size. Collapses can be caused naturally, as in the declining phase of multi-annual fluctuations and after natural disasters, or by man-made events, such as pesticide application. In general, there are three ways population recovery can occur: (1) in situ survival and multiplication of a small remaining fraction of the population; (2) immigration; or (3) a combination of the two. The recovery mechanism strongly depends on life history strategy, social behaviour and density-dependent processes in population dynamics of the species in question. In addition, the kind of disturbance, its intensity and spatial scale, as well as environmental circumstances (e.g. the presence and distance of refuge areas) have to be taken into account. Recovery time can vary from a couple of days to several years depending on the reproductive potential of the species and the type of disturbances, regardless of whether the collapse is man made or natural. Ultimately, most populations rebound to levels equal to numbers before the collapse. Based on current knowledge, case-by-case decisions seem appropriate for small-scale conservation. For pest control, a large-scale approach seems necessary. Further investigations are required to make sound, species-specific recommendations.

Case report: Emergence of autochthonous cutaneous leishmaniasis in northeastern Texas and southeastern Oklahoma

Autochthonous human cases of leishmaniasis in the United States are uncommon. We report three new cases of cutaneous leishmaniasis and details of a previously reported case, all outside the known endemic range in Texas. Surveys for enzootic rodent reservoirs and sand fly vectors were conducted around the residences of three of the case-patients during the summer of 2006; female Lutzomyia anthophora sand flies were collected at a north Texas and southeast Oklahoma residence of a case-patient, indicating proximity of a suitable vector. Urban sprawl, climatologic variability, or natural expansion of Leishmania mexicana are possible explanations for the apparent spread to the north and east. Enhanced awareness among healthcare providers in the south central region of the United States is important to ensure clinical suspicion of leishmaniasis, diagnosis, and appropriate patient management.

Sensationalistic journalism and tales of snakebite: are rattlesnakes rapidly evolving more toxic venom?

Recent reports in the lay press have suggested that bites by rattlesnakes in the last several years have been more severe than those in the past. The explanation, often citing physicians, is that rattlesnakes are evolving more toxic venom, perhaps in response to anthropogenic causes. We suggest that other explanations are more parsimonious, including factors dependent on the snake and factors associated with the bite victim's response to envenomation. Although bites could become more severe from an increased proportion of bites from larger or more provoked snakes (ie, more venom injected), the venom itself evolves much too slowly to explain the severe symptoms occasionally seen. Increased snakebite severity could also result from a number of demographic changes in the victim profile, including age and body size, behavior toward the snake (provocation), anatomical site of bite, clothing, and general health including asthma prevalence and sensitivity to foreign antigens. Clinical management of bites also changes perpetually, rendering comparisons of snakebite severity over time tenuous. Clearly, careful study taking into consideration many factors will be essential to document temporal changes in snakebite severity or venom toxicity. Presently, no published evidence for these changes exists. The sensationalistic coverage of these atypical bites and accompanying speculation is highly misleading and can produce many detrimental results, such as inappropriate fear of the outdoors and snakes, and distraction from proven snakebite management needs, including a consistent supply of antivenom, adequate health care, and training. We urge healthcare providers to avoid propagating misinformation about snakes and snakebites.