Basal Metabolic Rate and Maternal Energetic Investment Durations in Mammals

Background The Metabolic Theory of Ecology (MTE) predicts that gestation duration, lactation duration, and their sum, total development time, are constrained by mass-specific basal metabolic rate such that they should scale with body mass with an exponent of 0.25. However, tests of the MTE’s predictions have yielded mixed results. In an effort to resolve this uncertainty, we used phylogenetically-controlled regression to investigate the allometries of gestation duration, lactation duration, and total development time in four well-studied mammalian orders, Artiodactyla, Carnivora, Primates, and Rodentia. Results The results we obtained are not consistent with the predictions of the MTE. Gestation duration scaling exponents are below 0.25 in all four orders. The scaling exponent for lactation duration is below 0.25 in Carnivora and Rodentia, indistinguishable from 0.25 in Artiodactyls, and steeper than 0.25 in Primates. Total development time scales with body mass as predicted by the MTE in Primates, but not in artiodactyls, carnivores, and rodents. In the latter three orders, the exponent is 0.15. Conclusions Together, these results indicate that the influence of basal metabolic rate on mammalian maternal investment durations must be more complicated than the MTE envisages, and that other factors must play an important role. Future research needs to allow for the possibility that different factors drive gestation duration and lactation duration, and that the drivers of the two durations may differ among orders

Snowshoe hare abundance and foraging behaviour in recently burned forests

A combination of climate change and decades of fire suppression has led to an increase in the size of wildfires in North American conifer forests. Large wildfires are more heterogeneous than smaller fires because of their landscape context and fire-weather that ignites them. Larger fires are patchier, and have more opportunities for good habitat, but they also produce large patches of open area where prey species are exposed to predation. For many mammal species, such as snowshoe hares (Lepus americanus) this patchiness means having to navigate quite different habitat patches while trying to locate adequate cover and food. The density of animals in burns of different sizes, and how individuals behave while foraging in those within-burn patches, is unknown for many species. This study addresses these knowledge gaps (fire size and within-burn patchiness) with two studies. First, I assessed densities of snowshoe hare in 9 wildfires that burned 13 years ago (3 each of small (~100 ha), medium (1000-5000 ha), and large (>10,000 ha)) and in mature forests in southern British Columbia to determine if fire size impacts hare density. I found that hares were highly variable in large burns but when they were present the densities were the highest of any sites. Hares were absent from small burns and most medium burns. Hares were commonly present in mature forests but at much lower densities than in large burns. Second, I assessed snowshoe hare foraging behaviour by measuring tortuosity, speed of movement, and amount of browse along winter foraging pathways in open and regenerating patches of the Okanagan Mountain Park fire (>25,000 ha) and surrounding mature forest. I found that hares moved the fastest and browsed the least in open patches, and moved slower and ate more in sapling patches. Hares did not change tortuosity. The data from these two studies show that fire size is an important predictor of snowshoe hare density and that hares change foraging behaviour to some degree based on the type of habitat they are in.Arts and Sciences, Irving K. Barber School of (Okanagan)Biology, Department of (Okanagan)Graduat

Impact of wildfire size on snowshoe hare relative abundance in southern British Columbia, Canada

Background: Large wildfires result in more heterogeneous fire scars than do smaller fires because of differences in landscape context and high variability in burn intensity and severity. Previous research on mammal response to wildfire has often considered all fires as comparable disturbances regardless of size. Here, we explicitly examine whether fire size affects relative abundances of a keystone herbivore, snowshoe hare (Lepus americanus Erxleben, 1777), in regenerating stands of the same age. We surveyed vegetation and fecal pellets of snowshoe hares in nine 13-year-old wildfires, specifically, three fires in three size categories—small (80 to 200 ha), medium (1000 to 5000 ha), and large (>10 000 ha)—and in mature forests in southern British Columbia, Canada. Results: Snowshoe hare density was low (0.4 hares ha−1), but hares were present at 57% of mature sites. Hares were absent from all areas where small fires had burned and were found in only one medium area post fire (0.2 hares ha−1). Hares were found within the fire scars of all three large burned areas, and with much higher numbers (3.8 hares ha−1) than in the medium fire area or mature forest. Snowshoe hare abundance was highly correlated with the number of sapling trees, especially lodgepole pine (Pinus contorta Douglas ex Loudon). Sapling densities were highly variable, but dense stands of saplings were found only in burn scars from large wildfires. Conclusions: Fire size is an important predictor of snowshoe hare relative abundance in areas that are regenerating post fire; fires of different sizes are not comparable disturbances. Specifically, the post-fire heterogeneity after large fires enabled both the highest hare numbers as well as patches with no hares. These results suggest that forest and wildlife managers should protect areas with dense regeneration post fire, as these sites are necessary for hares after large wildfires.Arts and Sciences, Irving K. Barber School of (Okanagan)Biology, Department of (Okanagan)ReviewedFacult