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Population Biology Readings 1 and 2.docx

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Department
Biology
Course
Biology 3446B
Professor
Robert Solomon
Semester
Winter

Description
Morphological responses of white­tailed deer to a severe population reduction Abstract: - Document responses in terms of mass, hind-foot length and antler beam diameter of white-tailed deer (Odocoileus virginianus borealis) - Dressed weights and yearling antler beam diameters of Long Point National Wildlife Area (LPNWA), Lake Erie and Ontario deer are among the lowest on record for this subspecies - Notable increase between 1989 and 1990 and in 1994 - 1989-1994: Mean mass of male fawns increase by 44%; mean mass of yearling males increased by 96% and 75% for 2.5y/o bucks - Antler beam diameters increase by 93% in yearlings and 35% in 2.5 y/o bucls between 1989 and 1994 - The significant increases in mean hind-foot length were also noted in male and female fawns - The significant and immediate responses to decrease density and competition demonstrate that the herd was under extreme environmental stress and show the exceptional resiliency of this species in withstanding severe environmental pressure Introduction: - The body morphology of white-tailed deer (Odocoileus virginianus) is an important indicator of how it responds to the environment - This paper documents the morphological responses of a free-ranging herd of white-tailed deer to an approximate 85% reduction in population over a 5-year period in the chronically overpopulation Long Point National Wildlife Area (LPNWA) in southern Ontario - The herd reduction was effected by a series of controlled public hunts from 1989 to 1994 held as part of a management program designed to promote the regeneration of severely overbrowsed habitat - Carrying capacity of winter range in LPNWA in 1993 estimated to be 35-42 animals - Prior to to the 1989 deer hunt, there were approximately 500 deer wintering in the LPNWA - The abundance of poor-quality browse (vegetation) supplemented by herbaceous plants, and moderate winters due to lake effect, helped to sustain the population at a level well above the carrying capacity of preferred browse species Study Area: - Long Point – 32km, 6450-ha sand pit on the north shore of Lake Erie - Max width = 2km - Uplands are a series of northeast-southwest rolling parallel sand ridges separated by various types of wetlands - The property is not managed as National Wildlife Area by the Canadian Wildlife Services (CWS) of Environment Canada - Vegetation communities of LPNWA are determined by topography, soils, climate, past fires and chronic overbrowsing by white-tailed deer o Record indicate that the vegetation composition was once very different – “dense jungle”, “naturally produces many vines” o Now: “park-like conditions” - Savannah-like conditions on the peninsula have been exacerbated by the activities of people. Much of the good timber was logged from 1850s to 1950. Development of savannah-like conditions also facilitated by fires - Estimate 750 species of vascular plants - 42 provincially rare species and 3 nationally rare species - 4 forest communities - 4 savanna communities - Other types of vegetation communities found in the peninsula: beach, dry dune, wetland, and aquatic communities Methods: - Population estimates o Size of LPNWA herd estimated by means of winter driver counts in 1986 and 1988 o 1990 and on: snow and ice conditions unfavourable for winter counts o Estimates of natural mortality and recruitment cased on the 1989 and 1990 age structure of harvested animals o Jan 1986: 475 deer o Jan 1988: 500 deer o 1989: 405 deer o Jan 1990: 156 deer o 1994: 120 deer - Public hunt o Applicants chosen by random draw and required to apply and hunt as parties of 2-8 o Participants required to attend information seminar prior to the hunt o Each hunter allowed two deer – at least 1 must be antlerless o Hunters permitted to harvest up to the part limit of available tags and were required to used centre-fire rifles, shotguns, or muzzle loaders o Six 2 day hunts held in 1989 o Three 3 day hunts held in 1990 and 1994 - Morphometrics o All deer processed at mandatory check stations operated by the CWS o Variable assessed:  Dressed (eviscerated) weight  Hind-foot length  Antler beam diameter  Udder (milk present?)  Age Results and Discussion: - Dressed weights of LPNWA deer from 1989 are among the lowest on record for the species O. v. borealis o Comparable to those of deer in protected and severely overbrowsed Harriman State Park in New York – “some of the poorest specimens in physical conditions ever recorded in New York and possibly the Northeast” - Mean mass of male fawns increased by % from 1989 to 1990 and by 44% from 1989 to 1994 - Yearling males showed the greatest response – initial increase of 25% from 1989 to 1990 and an overall increase of 96% by 1994 - Mass of yearling females increased by 23% in 1990, and significantly by 50% from 1989 to 1994 - LPNWA fawns harvested in 1994 weighed less, but in 1994, LPNWA yearlings exhibited exceptional growth - Mean mass of animals aged 2.5 years also exhibited significant increases between 1989 and 1990, and between 1990 and 1994 o Overall increase of 75% for bucks and 48% for does - Differences in density appear to affect the body mass of bucks to a greater degree than that of does o Stag mass tends to be more responsive to differences in density than that of hinds, in which density effects are reflected to a greater degree in reproductive effort than in mass - Older animals typically exhibited a reduced but significant response when sample size was not limiting – evidence of low birth masses and poor conditions experiences during their early growth years - Skeletal growth has the highest priority among the three indices of morphology (mass, hind-foot length, antler beam diameter) and is least affected by differences in range quality - Hind-foot length showed the least response - Antler growth is subordinate to maintenance and general body growth, consequently antlers tend to be more responsive to environmental stress than other morphological indices o Excellent indicators of the physical condition of the herd - Antler beam diameter and body mass are closely related o As deer responded to reduced density and competition, the responses of antler beam diameter and dressed body weight were not uniform  This may be due to the relative improvement in the quality of winter and summer range in LPNWA - The body mass of the deer is controlled by the history of the animal to a greater degree than is antler growth - The autumn body mass of a deer is affected by the feeding conditions in the previous summer, spring, and winter o Antler growth is not as affected by winter food restrictions, but depends to a greater extent upon spring and early-summer feeding conditions - This is likely the most extreme case of white-tailed deer suppression and subsequent release ever documented - These results show that the environment was limiting its genetic potential, and illustrated the exceptional ability of the species to withstand severe environmental pressure Female survival rates in a declining white­tailed deer population Abstract: - Objective: identify seasonal and annual survival rates, in the context of habitat and other environmental conditions, necessary to identify ultimate causes of proximate mortality for white-tailed deer in the central Black Hills - 1993-1996: monitored collared female (n=73) white-tailed deer in the central Black Hills of South Dakota and Wyoming - Natural mortality (coyotes, dogs, malnutrition, sickness) was the primary cause of mortality (71%), followed by harvest (22.6%) and accidental causes (6.5%) - More females died in spring (n=33) than in the call (n=14), winter (n=9), or summer (n=6) - For the entire study period (1993-1996), survival rate for female white-tailed deer was 10.4% - Annual survival rates of females ranged from 50.3-62.1% and were similar among years - Intraseasonal survival rates for females differed between winter and spring, whereas summer and fall were similar - High spring mortality of females
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