The effects of grassland degradation on the genetic structure of a small mammal

Grassland degradation is challenging the health of grassland ecosystems globally and causing biodiversity decline. Previous studies have demonstrated the impact of grassland degradation on the abundance and behavior of small mammals. Little is known about how it affects the genetic structure of gregarious mammals in the wild. This study explores the effects of grassland degradation on the genetic structure of a small burrowing mammal, plateau pika (Ochotona curzoniae). We used nine microsatellite loci to analyze the genetic diversity and genetic differentiation between colonies and genetic relatedness between individuals within the colony. We found that pikas in severely degraded grasslands had a significantly higher genetic diversity within colonies, a higher level of gene flow between colonies, and a lower genetic differentiation between colonies compared to pikas in less degraded grasslands. Individuals within colonies had a significantly lower genetic relatedness in severely degraded grasslands than in less degraded grasslands. This study has provided potential evidence of a significant impact of grassland degradation on the genetic structure of pikas, which has caused a breakdown of their kin-selected colony structure.

Determining Extinction for Small Cryptic Species: The Morro Bay Kangaroo Rat

One third of missing mammal species thought to be extinct have been rediscovered. Determining extinction correctly, without misinterpreting negative evidence, is difficult and takes significant effort, especially for small, cryptic species. The Morro Bay kangaroo rat (MBKR), Dipodomys heermanni morroensis, is a small nocturnal rodent suspected of being extinct. This is because it has not been seen since 1986 despite three range-wide surveys conducted between 1995 and 2012, a recent scent-detecting dog survey, and over a dozen localized surveys. Causes of decline have been reported and the primary causes are thought to be development-driven habitat loss and ecological succession. Given this, we suspect that if the MBKR is extant, then it occurs in the periphery of its historical range. We summarize a survey of the Morro Bay sandspit, an area not previously considered part of MBKR’s range but that has the potential to be occupied. Inferences from the subspecies’ closest relative, Dipodomys heermanni arenae, were used to inform surveys and detection probability estimates for MBKR. Visual surveys of the sandspit in areas with the greatest probability of displaying signs yielded few occurrences of possible signs. Camera traps were deployed in winter and summer at locations with possible signs, but, despite occupancy model detection probabilities of 0.88 in winter and 0.97 in summer, there were no detections of MBKR. Given detection probability estimates inferred from Dipodomys heermanni arenae, the conditional occupancy estimate that MBKR are present on the sandspit but were missed by all cameras on all nights of surveying is extremely low (5 × 10−6). We conclude that the MBKR is not present on the Morro Bay sandspit, at least not in the habitat where its presence was most likely to be detected. Future surveys for this small, cryptic species will need to adapt to a combination of low expected occupancy and high expected detection probability.

Survey for Morro Bay Kangaroo Rat: A Rare Mammal of Uncertain Status

The Morro Bay kangaroo rat Dipodomys heermanni morroensis is a small, nocturnal, burrowing rodent endemic to the vicinity of Morro Bay in San Luis Obispo County, California. It was listed as endangered pursuant to the U.S. Endangered Species Act in 1973. Despite many searches over three decades, the Morro Bay kangaroo rat has not been captured or sighted in the wild since 1986. While recognizing that the Morro Bay kangaroo rat may be extinct, two of us in a previous paper also speculated it may be persisting at extremely low density in isolated colonies and recommended surveying with wildlife scent-detection dogs and baited camera traps. We searched with a wildlife scent-detection dog and baited camera traps in four historically occupied areas and detected no Morro Bay kangaroo rats. Unfortunately, our data combined with all other existing data do not allow us to conclude whether the Morro Bay kangaroo rat is extinct or extant. Essentially, the International Union for the Conservation of Nature international standard has not been met to make a definitive determination of extinction. That is, a species should be considered extinct only when there is no reasonable doubt that the last individual has died. We acknowledge that because of resource limitation we surveyed only a small sample of the numerous patches of habitat in the expansive landscape. Further, we now consider the Morro Bay sand spit (total area 4.35 km2, foredunes 3.75 km2), a peripheral area, as potentially part of the geographic range with suitable habitat, and it has never been searched. Therefore, considering all available information, we conclude that the Morro Bay kangaroo rat must be considered as possibly extant. We recommend that search efforts continue in several specific areas, including the Morro Bay sand spit. If the Morro Bay kangaroo rat still exists, it will be challenging and difficult to rediscover because of its likely low density and patchy distribution in the expansive landscape, combined with its small size, nocturnal nature, and secretive lifestyle.