scholarly journals Population Ecology of Caribou Populations without Predators: Southampton and Coats Island Herds

Rangifer ◽  
1996 ◽  
Vol 16 (4) ◽  
pp. 17 ◽  
Author(s):  
Jean-Pierre Quellet ◽  
Douglas C. Heard ◽  
Robert Mulders
Keyword(s):  
Food Availability ◽  
Weather Conditions ◽  
Food Competition ◽  
Plant Production ◽  
Population Increase ◽  
Delayed Puberty ◽  
Winter Food ◽  
Capita Food ◽  
Competition For Food ◽  
Per Capita

This paper is a review of the ecology of two caribou populations inhabiting predator-free northern islands, Coats and Southampton Island. Findings are analyzed in light of the hypothesis that in absence of prédation or high human harvest, food competition results in delayed puberty, reduced calf production, increased winter starvation of caribou and regulates populations at high densities (>2 km-2). Caribou were hunted to extinction on Southampton Island (Northwest Territories, Canada) by mid-century. In 1967, 48 caribou were captured on neighbouring Coats Island and released on Southampton Island. Southampton Island is characterized by a high per capita winter food availability in summer and in winter. The population on Southampton Island has been increasing at a rapid rate of growth since re-introduction (Lamba=1.27). Fast population growth was possible because females invested early in reproduction and over winter survival rate was high. The population on Coats Island is also characterized by high per capita food availability in summer but low food availability in winter. The population size has undergone some marked fluctuations, abrupt declines followed by relatively rapid recovery and, contrary to predictions, densities were always less than 1 km-2. Low population densities on Coats Island result primarily from low food availability. This review suggests that in the absence of prédation or high human harvest competition for food regulates caribou population abundance. However, caribou numbers can fluctuate markedly among years because inter-annual variation of weather conditions affects forage accessibility in winter. This review also emphasizes the importance of distinguishing between factors that determine absolute population density and variation in density among years (in our case probably plant production and winter weather conditions which influence forage accessibility) from the regulatory factors, processes that stop population increase (competition for winter food leading primarily to density dependent changes in mortality from starvation) when examining population dynamics.

scholarly journals Ecology of the Porcupine caribou herd

Rangifer ◽  
1996 ◽  
Vol 16 (4) ◽  
pp. 45 ◽  
Author(s):  
Kenneth R. Whitten
Keyword(s):  
Rangifer Tarandus ◽  
Climatic Factors ◽  
Weather Conditions ◽  
Nutritional Stress ◽  
Food Competition ◽  
Limiting Factors ◽  
Delayed Puberty ◽  
Adverse Weather Conditions ◽  
Adverse Weather ◽  
Long Time

Researchers have described general patterns of population regulation that fit most caribou (Rangifer tarandus) herds. Nevertheless, specific factors operating on particular populations vary greatly, and efforts to categorize herds according to the general patterns often lead to confusion. It is difficult for biologists to attempt to describe population dynamics in terms of density relationships for wide-ranging arctic caribou such as the Porcupine Herd. In these herds density varies as a function of dispersal and erratic movement patterns and is not simply the number of caribou divided by a fixed range area. Density is also a poor surrogate for resource availability per individual caribou because climatic factors affect forage and/or access to forage independendy of caribou numbers. Thus classic signs of nutritional stress such as delayed puberty, reduced productivity, and winter starvation can occur when a population is small as well as large and do not necessarily denote food competition brought on by high density, per se. Nutritional stress and exacerbated predation due to adverse weather conditions occasionally cause the Porcupine Herd to decline, and limiting factors such as poor nutrition, predation, harvest, accidents, and disease act in combination to keep herd growth rates low during periods of good weather. Adverse weather setbacks occur frequently, and the herd remains within a fairly restricted range of densities over long time periods. There is no true density dependent regulation and no equilibrium in this system.

Food Competition in Brown Capuchin Monkeys (Cebus Apella): Quantitative Effects of Group Size and Tree Productivity

Behaviour ◽  
1988 ◽  
Vol 105 (1-2) ◽  
pp. 53-76 ◽  
Author(s):  
Charles H. Janson
Keyword(s):  
Food Intake ◽  
Group Size ◽  
Food Competition ◽  
Capuchin Monkeys ◽  
Feeding Time ◽  
Net Energy ◽  
Large Trees ◽  
Capita Food ◽  
Per Capita ◽  
Large Groups

AbstractThe effects of group size and fruit availability in tree crowns on per-capita food intake was examined for wild brown capuchin monkeys living in groups of 3-12 individuals. Per-capita feeding time was nearly exactly inversely proportional to group size in small-crowned trees with little fruit, but was essentially independent of group size in large-crowned trees with abundant fruit. Despite the use of such productive trees, per-capita feeding time in the average tree visited decreased by 50% over a 4-fold range of group sizes. This cost of indirect food competition in large groups was not compensated by increased rates of ingestion, preferential use of large trees, of a higher rate of fruit tree encounter per distance travelled. Instead, foraging effort (distance travelled, number of minutes devoted to foraging, total activity minutes per day) increased at large group sizes. Estimates of total energy intake and expenditure suggest that net energy gain is constant for individuals in group sizes of 5-12. I suggest that the upper limit to group size is set by the daylength available for foraging in large groups. Aggression in food trees increased in frequency in larger groups, but the relative feeding rates of dominants and subordinates of a given rank did not appear to depend on group size. Observed decreases in per-capita food intake due to either indirect or aggressive food competition within large groups are substantially greater than the 4% gain in mean food intake that large groups achieve by displacing smaller groups from fruit trees.

An experimental test of the ecological mechanisms driving density-mediated carry-over effects in a seasonal population

2020 ◽  
Vol 98 (7) ◽  
pp. 425-432
Author(s):  
Joseph B. Burant ◽  
Aidan Griffin ◽  
Gustavo S. Betini ◽  
D. Ryan Norris
Keyword(s):  
Food Availability ◽  
Reproductive Output ◽  
Individual Performance ◽  
Breeding Period ◽  
Conspecific Density ◽  
Capita Food ◽  
Ecological Mechanisms ◽  
Per Capita ◽  
Carry Over ◽  
High Degree

Carry-over effects occur when past experience influences current individual performance. Although variation in conspecific density in one season has been shown to carry over to influence dynamics in the following season, the proximate ecological mechanisms driving these effects are unknown. One hypothesis is that high density decreases food availability, resulting in poor physiological condition, which in turn compromises performance the next season. Alternatively, high conspecific density could also lead to a high degree of antagonistic interactions, decreasing the amount of time individuals spend foraging. To investigate these hypotheses, we applied a factorial design where both conspecific density and per capita food availability during the non-breeding period were independently manipulated in seasonal populations of common fruit flies (Drosophila melanogaster Meigen, 1830). Individual condition at the beginning of the breeding period was influenced by per capita food availability but not density during the previous non-breeding period. In contrast, reproductive output was most strongly influenced by the interaction between per capita food availability and density in the previous non-breeding period, such that populations that experienced high non-breeding densities and low food availability had the lowest reproductive output. However, the strength of this effect was relatively weak. Our results demonstrate how environmental and social conditions in one part of the annual cycle can carry over to influence individual performance in subsequent periods.

scholarly journals Toward a Dualistic Growth? Population Increase and Land-Use Change in Rome, Italy

Land ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 749
Author(s):  
Leonardo Bianchini ◽  
Gianluca Egidi ◽  
Ahmed Alhuseen ◽  
Adele Sateriano ◽  
Sirio Cividino ◽  
...  
Keyword(s):  
Land Use ◽  
Land Use Change ◽  
Population Growth ◽  
Mediterranean Basin ◽  
Urban Expansion ◽  
Arable Land ◽  
Central Italy ◽  
Agricultural Landscapes ◽  
Population Increase ◽  
Per Capita

The spatial mismatch between population growth and settlement expansion is at the base of current models of urban growth. Empirical evidence is increasingly required to inform planning measures promoting urban containment in the context of a stable (or declining) population. In these regards, per-capita indicators of land-use change can be adopted with the aim at evaluating long-term sustainability of urbanization processes. The present study assesses spatial variations in per-capita indicators of land-use change in Rome, Central Italy, at five years (1949, 1974, 1999, 2008, and 2016) with the final objective of quantifying the mismatch between urban expansion and population growth. Originally specialized in agricultural productions, Rome’s metropolitan area is a paradigmatic example of dispersed urban expansion in the Mediterranean basin. By considering multiple land-use dynamics, per-capita indicators of landscape change delineated three distinctive waves of growth corresponding with urbanization, suburbanization, and a more mixed stage with counter-urbanization and re-urbanization impulses. By reflecting different socioeconomic contexts on a local scale, urban fabric and forests were identified as the ‘winner’ classes, expanding homogeneously over time at the expense of cropland. Agricultural landscapes experienced a more heterogeneous trend with arable land and pastures declining systematically and more fragmented land classes (e.g., vineyards and olive groves) displaying stable (or slightly increasing) trends. The continuous reduction of per-capita surface area of cropland that’s supports a reduced production base, which is now insufficient to satisfy the rising demand for fresh food at the metropolitan scale, indicates the unsustainability of the current development in Rome and more generally in the whole Mediterranean basin, a region specialized traditionally in (proximity) agricultural productions.

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