Perturbation analysis of competition and overlap in habitat utilization between Dipodomys ordii and Dipodomys merriami

Summary The populations of two coexisting species of Dipodomys (Heteromyidae, Rodentia) were manipulated on 10, large, unenclosed, trapping grids. These manipulations revealed that, although many kangaroo rats are established residents in an area, a large number are transient individuals who quickly occupy vacated habitats. On plots from which residents had been removed, transients settled at rates of up to 5% of carrying capacity per day. These immigrants were invariably of the same species that was removed, indicating a strong element of intraspecific competition with little or no evidence of competition between the species.Trapping records suggest that these species avoid competition through habitat selection. Dipodomys ordii prefer a grassier habitat, and D. merriami a habitat dominated by creosote bush. Apparent overlap in their utilization of habitats, based on sites of capture, predicts competition coefficients to be higher than those permitted by the theory of limiting similarity and much higher than those actually shown by the perturbation experiments.This study demonstrates the dangers of estimating alpha without experimentation. This is especially true in cases where habitat selection may be important, since organisms may travel in habitats without collecting resources therein. Our results are discussed in light of a theory which examines the optimal (rather than tolerable) amount of overlap in habitat utilization between two potential competitors in a mixed habitat. This theory predicts that the pressure of natural selection should eliminate the interspecific competition entirely.However, the conclusion that the interspecific competitive alpha is zero does not lead to the conclusion that interspecific competition is unimportant in the system. Instead, if our interpretation is correct, such competition has molded the system, and were there not a continual threat of interspecific competition, the habitat specializations would soon disappear.     

Biotic and abiotic effects on endoparasites infecting Dipodomys and Perognathus species

Between 1989 and 1998, 3,504 rodents of the genera Dipodomys and Perognathus were collected from 4 permanent collecting sites on the University of New Mexico's Long Term Ecological Research station, located on the Sevilleta National Wildlife Refuge (SNWR), Socorro County. New Mexico. All animals were killed and examined for endoparasites (acanthocephalans, cestodes, coccidia, and nematodes). The present report focuses on 3 endoparasite groups, cestodes, coccidia, and nematodes. Specific analyses address how prevalence changes were related to abiotic factors such as habitat, season, or precipitation, and how prevalence of each parasite species in each host species differed in relation to host age, host sex, host reproductive status, host body mass, host density, parasite-parasite interactions, and host specificity. A logistic regression was used to determine which host characters and which abiotic factors are correlated with a parasite infection. Significant variables for at least half of the parasites include season, site, and winter precipitation. However, no parasite prevalences were correlated, and significant variables were not identical between parasites, indicating that each parasite species varied independently and that no generalizations can be drawn. The parasite prevalences in these rodents on the SNWR vary in independent and complex ways.     

Captive reproduction in Heermann's kangaroo rat,Dipodomys heermanni

This paper summarizes 8 years of captive breeding experience with the endangered Morro Bay kangaroo rat (Dipodomys heermanni morroensis) and the non-endangered Lompoc kangaroo rat (D. h. arenae), a related form used as a surrogate. Kangaroo rats are aggressive and must be caged individually; copulation can only take place when the female is in estrus. The estrous cyle varies, but is usually 14–17 days long; gestation averages 31 days. Data on development of the young, animal health, mortality, and longevity are presented. The productivity of this project is compared with that of another long-term kangaroo rat breeding project in terms of the number of young produced per female per year. A captive breeding program can be initiated with 40–50 reproductive animals as a founder group.     

Spatial population structure in the banner-tailed kangaroo rat,Dipodomys spectabilis

I attempted to characterize spatial units of local dynamics and dispersal in banner-tailed kangaroo rats (Dipodomys spectabilis), to determine if spatial structure influenced population dynamics in the way predicted by current metapopulation models. D. spectabilis exhibited a hierarchical spatial structure. Local populations that appeared as discrete entities on a scale of kilometers were subdivided into clusters of mounds on a scale of meters. This structure, however, cannot be characyerized in terms of the discrete habitat patches envisioned by the metapopulation models. Occupied areas were statistically distinguishable from the surrounding matrix, but this difference was only quantitative. There were no discrete boundaries between occupied areas and the matrix. Habitat within occupied areas was heterogeneous, and occupied areas in different locations were statistically distinguishable from each other. High heterogeneity within occupied areas, and high contrast among them, make it difficult to define what is a suitable habitat patch for D. spectabilis. On a smaller spatial scale, there was significant aggregation of resident mounds within occupied areas. These aggregations, however, do not correspond to discrete habitat patches. Rather, they appear to result from an interaction between fine-scale habitat heterogeneity and limited dispersal due to natal philopatry and low adult vagility. These complications make it difficult to identify habitat patches independent of the species' distribution. For species like D. spectabilis that are patchily distributed but do not occupy discrete habitat patches, a patch occupancy approach does not seem appropriate for describing spatial structure. Hierarchical spatial structure underscores the need for a framework that incorporates multiple scales of spatial structure, rather than one that pre-imposes a single spatial scale as being important for population dynamics. A framework that (i) considers patchiness as a combination of both habitat heterogeneity, and life-history and behavioral characteristics, and (ii) incorporates hierarchical spatial structure, appears to be the most suitable for conceptualizing spatial dynamics of behaviorally complex vertebrates such as D. spectabilis.     

Seismic communication between the burrows of kangaroo rats, Dipodomys spectabilis

Banner-tailed kangaroo rats, Dipodomys spectabilis, footdrum to produce substrate-borne and airborne acoustic energy. Previous studies show that they communicate territorial ownership via airborne footdrumming signals. The research reported here used simulated footdrum patterns generated by an artificial `thumper' to address the question of whether kangaroo rats communicate through seismic components of these acoustic signals. With microphones suspended in sealed burrows, we found that airborne sounds were attenuated by approximately 40 dB as they passed through the burrow wall into the burrow chamber. The substrate-borne vibrations from the thumper yielded sound approximately 40 dB greater in peak amplitude than the attenuated airborne sound. Thus, 99.9% of the peak power of the thumper was transmitted directly through the substrate into the burrow. The rats in sealed burrows timed their responses to playbacks of footdrums from the thumper and a loudspeaker so they did not initiate a drumming sequence during either the seismic or airborne signals. When these signals were masked by loud noise, the rats continued to drum to the seismic signal but drummed randomly during the airborne playback. These results suggest that the sealed burrow provides a quiet place in which D. spectabilis can listen for substrate-borne communications from conspecifics. Accepted: 13 May 1997     

Neighbor Recognition in a Solitary Desert Rodent (Dipodomys merriami)

Neighbor recognition in the Merriam's kangaroo rat (Dipodomys merriami) was tested in neighbor and nonneighbor pairs of the same and opposite sex in a large enclosure in the field. Mutual tolerance, rather than aggression, occurred in the encounters, and neighbor recognition was more apparent in females than in males. Females tolerated and engaged in nonagonistic contact with familiar males and females; males approached and attempted to contact neighbors and nonneighbors alike. Neighbor recognition is important to both spacing and mating in females. Males' persistent attempts to interact with any conspecific may be important to their mating success.     

Chromosome banding and DNA replication studies on a cell line of Dipodomys merriami

The chromsomes of a cell line of Dipodomys merriami are described in terms of their C-, G- and Q-banding patterns. Studies on the buoyant density of DNA made at different times in the S phase show that the replication of HSα satellite and AT-rich main band DNA occurs preferentially late in the S phase, whereas MS satellite and GC-rich main band DNAs are replicated early in the S phase. Autoradiographic studies of chromosomes labelled early or late in the S phase are used to relate the banding patterns nf particular chromosome regions to the fraction of DNA which they may contain.     

Factors affecting pair compatibility in captive kangaroo rats,Dipodomys heermanni

Captive propagation is a critical component of the Morro Bay Kangaroo Rat Recovery Plan, but past attempts to breed this and other kangaroo rat species have had mixed success. In three experiments using a closely related surrogate species, the Lompoc kangaroo rat, we evaluated the effects of familiarity and long-term housing experience on the behavior of captive males and females during dyadic encounters in an attempt to devise husbandry methods most conducive to reproduction. Females exhibited less aggression with and were more likely to allow physical contact with familiar males, provided the males had had previous social experience, such as that provided by living in close sensory contact with female conspecifics. Socialized males (those housed adjacent to females, separated from them by a wire mesh screen) were cautious, rather than persistent, when interacting with unfamiliar or anestrous females. Males housed in isolation from conspecifics were persistent whether or not they were familiar to the female. Pairs with very long periods of familiarity exhibited more nonaggressive contact than newly acquainted pairs. Results suggest that housing structures allowing longterm sensory contact between potential mates may improve breeding success in kangaroo rats and other solitary, aggressive species. © 1995 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Search for lunar periodicity in the bannertail kangaroo rat (Dipodomys spectabilis)

Abstract

The endogenous activity cycle of the nocturnal bannertail kangaroo rat was investigated. Although bannertail activity is a function of the lunar day as well as the solar day, all ten subjects exhibited free‐running activity periods of solar‐day length; there was no evidence of an endogenous lunar‐day cycle. Animals were provided with a burrow system and a small pseudo‐desert, a laboratory facility in which animal activity data closely resembled measurements taken in the field. Several analytical techniques for quantifying the data were utilized, and one, the mean interval of activity, is recommended to other investigators.