Demography Of Sympatric Arctic And Snowshoe Hare Populations

Author : Jacob Scott Ivan
Publisher :
ISBN 13 :
Total Pages : 141 pages
Book Rating : 4.:/5 (758 download)

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Download or read book Density, Demography, and Seasonal Movements of Snowshoe Hares in Central Colorado written by Jacob Scott Ivan and published by . This book was released on 2011 with total page 141 pages. Available in PDF, EPUB and Kindle. Book excerpt: Snowshoe hares (Lepus americanus), their famous 10-year population cycle, and close association with Canada lynx (Lynx canadensis) have been well-studied in boreal Canada for decades. Snowshoe hare range, however, extends south into the Sierra Nevada, Southern Rockies, upper Lake States, and Appalachian Mountains. Ecology of snowshoe hares in these more southerly regions is not as well understood, though hare research in the U.S. Rocky Mountains has accelerated over the past decade. Through this recent work, biologists have identified stands of young, densely-stocked conifers and those of mature, uneven-aged conifers as primary hare habitat in the region. Both stand types are characterized by dense understory vegetation that provides both browse and protection from elements and predators. From 1999 to 2006, Canada lynx were reintroduced into Colorado in an effort to restore a viable population to the southern portion of their former range. Snow tracking of released individuals and their progeny indicated that the majority of lynx winter diet in Colorado was comprised of snowshoe hares. Thus, long-term success of the lynx reintroduction effort hinges, at least partly, on maintaining adequate and widespread populations of snowshoe hares in the state. To improve our understanding of snowshoe hare ecology in the southern portion of their range, and enhance the ability of agency personnel to manage subalpine landscapes for snowshoe hares and lynx in Colorado, I conducted an observational study to evaluate purported primary hare habitat in the state. Specifically, I estimated snowshoe hare density, survival, recruitment, and movement indices in mature, uneven-aged spruce/fir (Picea engelmannii/Abies lasiocarpa) and 2 classes of young, even-aged lodgepole pine: 1) "small" lodgepole pine (Pinus contorta) stands, which were clear cut 20-25 years prior to this study and had regenerated into densely stocked stands with trees 2.54-12.69 cm in diameter, and 2) "medium" lodgepole pine stands (tree diameter = 12.70-22.85 cm) which were clear cut 40-60 years prior to this study and pre-commercially thinned ~20 years prior. I used a combination of mark-recapture and radio telemetry to estimate parameters. I sampled during both summer and winter to cover the range of annual variation in parameters. Animal density is one of the most common and fundamental parameters in wildlife ecology and was the first metric I used to evaluate the stand types. However, density can be difficult to estimate from mark-recapture data because animals move on and off of a trapping grid during a sampling session (i.e., lack of geographic closure). In Chapter 1, I developed a density estimator that uses ancillary radio telemetry locations, in addition to mark-recapture information, to account for lack of geographic closure resulting in relatively unbiased estimates of density. I derived the variance for this estimator, showed how individual covariates can be used to improve its performance, and provided an example using a subset of my snowshoe hare data. In Chapter 2, I completed a series of simulations to test the performance of this "telemetry" estimator over a range of sampling parameters (i.e., capture probabilities, sampling occasions, densities, and home range configurations) likely to be encountered in the field. I also compared the percent relative bias of the telemetry estimator to two other commonly used, contemporary estimators: spatially explicit capture-recapture (SECR), and mean maximum distance moved (MMDM). The telemetry estimator performed best over most combinations of sampling parameters tested, but was inferior to SECR at low capture probabilities. The telemetry estimator was unaffected by home range configuration, whereas performance of SECR and MMDM was dependent on home range shape. Density is an important metric of habitat quality, but it can be misleading as some habitats with high animal density may function as population sinks. A complete assessment of habitat quality requires estimation of habitat-specific demographic rates in addition to density. In Chapter 3, I used the telemetry estimator to estimate snowshoe hare densities in each stand type during summer and winter, 2006-2009. I then combined mark-recapture and telemetry data to estimate survival via the Barker robust design model as implemented in Program MARK. Finally, I used age- and habitat-specific density and survival estimates to estimate recruitment in each stand type. During summer, hare densities were highest in small lodgepole (0.20 ± 0.01 (SE) to 0.66 ± 0.07 hares/ha), lowest in medium lodgepole pine (0.01 ± 0.04 to 0.03 ± 0.03 hares/ha), and intermediate in spruce/fir (0.01 ± 0.002 to 0.26 ± 0.08 hares/ha). During winter, densities became more similar among the 3 stand types. Annual survival was highest in spruce/fir (0.14 ± 0.05 (SE) to 0.20 ± 0.07) and similar among the 2 lodgepole stands types (0.10 ±0.03 to 0.16 ± 0.06). Across stands, summer-winter survival was nearly twice as high as winter-summer survival. Recruitment of juvenile hares occurred during all 3 summers in small lodgepole stands, 2 of 3 summers in spruce/fir stands, and in only 1 of 3 summers in medium lodgepole. Stand attributes indicative of dense cover were positively correlated with density estimates and explain relatively more process variance in hare densities than other attributes. These same attributes were not positively correlated with hare survival. In addition to density and demography, movement is an informative aspect of animal ecology. Timing, extent, and frequency of movements can reflect predation pressure, food scarcity/abundance, availability of mates, or seasonal changes in any of these parameters. In Chapter 4, I used telemetry data to assess movement patterns of snowshoe hares at 2 scales (within-season, between-season) in all 3 stand types. Within-season movements of hares were larger during winter than during summer and tended to be larger in small lodgepole stands. Within-season movements of males tended to be larger than females during summer, possibly as a means of maximizing mating opportunities. Movements were similar between the sexes during winter. Hares in both small and medium lodgepole stands tended to make larger movements between seasons than hares in spruce/fir stands, possibly reflecting the variable value of these stands as mediated by snow depth. In summary, snowshoe hare density, survival, and recruitment were relatively low in thinned, medium lodgepole stands compared to spruce/fir or small lodgepole. Thus, while hares occur in these stands, they do not appear to be capable of supporting self-sustaining hare populations, and this stand type is probably less important than mature spruce/fir and small lodgepole stand types. Management for snowshoe hares (and lynx) in central Colorado should focus on maintaining the latter. Given the more persistent nature of spruce/fir compared to small lodgepole, and the fact that such stands cover considerably more area, mature spruce/fir may be the most valuable stand type for snowshoe hares in the state.