Reconstruction of the historical range alters niche estimates in an endangered rodent

Defining historical baselines is critical for species conservation. Under the niche reduction hypothesis, species in decline may be restricted disproportionately from parts of their environmental niche. This bias likely has important implications for modeling species’ distributions if only contemporary occurrences (i.e. post‐range reduction) are used, because suitable habitat will be classified as unsuitable. Unfortunately, robust historical occurrence data is rarely available for sensitive species. In this study, we documented historical locations of the endangered, keystone giant kangaroo rat Dipodomys ingens by examining aerial imagery for burrow mounds. These burrow mounds are readily identifiable and distinguishable from other soil disturbances. We found giant kangaroo rat burrows well outside the currently accepted estimate of their historical distribution. Following the niche reduction hypothesis, we found that giant kangaroo rats have been extirpated from the flattest, hottest, driest parts of their range due to agricultural conversion. This reduction in their realized niche led to significant changes between historical and contemporary models of their distribution. We found that giant kangaroo rats may have occupied up to 56% more habitat historically than currently believed. Our results provide new guidance for managers working on restoration and habitat protection for this ecosystem engineer. This study highlights the critical importance of modeling historical distributions using the entire environmental niche once occupied by species of conservation need.     

On valuing patches: estimating contributions to metapopulation growth with reverse-time capture-recapture modelling

Metapopulation ecology has historically been rich in theory, yet analytical approaches for inferring demographic relationships among local populations have been few. We show how reverse-time multi-state capture-recapture models can be used to estimate the importance of local recruitment and interpopulation dispersal to metapopulation growth. We use 'contribution metrics' to infer demographic connectedness among eight local populations of banner-tailed kangaroo rats, to assess their demographic closure, and to investigate sources of variation in these contributions. Using a 7 year dataset, we show that: (i) local populations are relatively independent demographically, and contributions to local population growth via dispersal within the system decline with distance; (ii) growth contributions via local survival and recruitment are greater for adults than juveniles, while contributions involving dispersal are greater for juveniles; (iii) central populations rely more on local recruitment and survival than peripheral populations; (iv) contributions involving dispersal are not clearly related to overall metapopulation density; and (v) estimated contributions from outside the system are unexpectedly large. Our analytical framework can classify metapopulations on a continuum between demographic independence and panmixia, detect hidden population growth contributions, and make inference about other population linkage forms, including rescue effects and source-sink structures. Finally, we discuss differences between demographic and genetic population linkage patterns for our system.     

Further studies of Dirofilaria roemeri (Nematoda: Filarioidea) in naturally and experimentally infected Macropodidae.

Larval development of D. roemeri occurs in the subcutaneous and intermuscular connective tissue and intramuscularly in the pelvic region and hind limbs of the wallaroo and eastern grey kangaroo. Host response to developing larvae is not evident at 1, 14 and 28 days. The development of D. roemeri in the red kangaroo exhibits features previously observed in both normal and abnormal hosts. Low-level blood microfilaraemia of brief duration occurs in the red kangaroo, which may act as a secondary reservoir of infection for other kangaroo and wallaby species. Among commercially harvested Macropodidae in Queensland there is a greater prevalence of D. roemeri in wallaroos and grey kangaroos than in red kangaroos. Infection is most prevalent in animals from south-central and south-western districts.     

Structure and function of the eastern grey kangaroo (Macropus giganteus) foot thump

Most species of the family Macropodidae (kangaroos and wallabies) make a distinctive foot thump by striking the ground with their hind feet when they detect potential danger. I used the eastern grey kangaroo Macropus giganteus as a model to examine (1) the acoustic characteristics and structure of the thump, (2) the social context in which free-ranging kangaroos thumped when approached by a human observer on foot and (3) the intended recipient of the signal. Thumps were about two-thirds of a second in length, generally composed of two noisy pulses, and had the majority of the signal energy below 7 kHz. Only adult kangaroos, of both sexes, were observed to thump. A higher proportion of solitary kangaroos thumped than grouped kangaroos, and a higher proportion of kangaroos thumped when visibility was poor, either because of habitat type or low light levels. Given the context in which thumps were given, the foot thump appears to be a signal to a potential predator with three possible functions: to startle, signal detection or deter pursuit.     

Populations at risk: conservation genetics of kangaroo mice (Microdipodops) of the Great Basin Desert

The Great Basin Desert of western North America has experienced frequent habitat alterations due to a complex biogeographic history and recent anthropogenic impacts, with the more recent alterations likely resulting in the decline of native fauna and flora. Dark (Microdipodops megacephalus) and pallid (M. pallidus) kangaroo mice are ecological specialists found within the Great Basin Desert and are potentially ideal organisms for assessing ecosystem health and inferring the biogeographic history of this vulnerable region. Herein, newly acquired nuclear‐encoded microsatellite loci were utilized to assess patterns of variation within and among spatially discrete groups of kangaroo mice and to evaluate gene flow, demographic trends, and genetic integrity. Results confirm that there are at least three genetically distinct units within M. megacephalus and two such units within M. pallidus. The three units of M. megacephalus appear to have different demographic histories, with effectively no gene flow among them since their divergence. Similarly, the two units of M. pallidus also appear to have experienced different demographic histories, with effectively no gene exchange. Contemporary effective population sizes of all groups within Microdipodops appear to be low (<500), suggesting that each genetic lineage may have difficulty coping with changing environmental pressures and hence may be at risk of extirpation. Results of this study indicate that each Microdipodops group should be recognized, and therefore managed, as a separate unit in an effort to conserve these highly specialized taxa that contribute to the diversity of the Great Basin Desert ecosystem.