Regulation Hypothesis (regulation + hypothesis)

Distribution by Scientific Domains


Selected Abstracts


Dynamics of an age-structured population drawn from a random numbers table

AUSTRAL ECOLOGY, Issue 4 2000
Bertram G. Murray JR
Abstract I constructed age-structured populations by drawing numbers from a random numbers table, the constraints being that within a cohort each number be smaller than the preceding number (indicating that some individuals died between one year and the next) and that the first two-digit number following 00 or 01 ending one cohort's life be the number born into the next cohort. Populations constructed in this way showed prolonged existence with total population numbers fluctuating about a mean size and with long-term growth rate (r) , 0. The populations' birth rates and growth rates and the females' per capita fecundity decreased significantly with population size, whereas the death rates showed no significant relationship to population size. These results indicate that age-structured populations can persist for long periods of time with long-term growth rates of zero in the absence of negative-feedback loops between a population's present or prior density and its birth rate, growth rate, and fecundity, contrary to the assumption of density-dependent regulation hypotheses. Thus, a long-term growth rate of zero found in natural populations need not indicate that a population's numbers are regulated by density-dependent factors. [source]


Dynamics of an age-structured population drawn from a random numbers table

AUSTRAL ECOLOGY, Issue 4 2000
BERTRAM G. MURRAY JR
Abstract I constructed age-structured populations by drawing numbers from a random numbers table, the constraints being that within a cohort each number be smaller than the preceding number (indicating that some individuals died between one year and the next) and that the first two-digit number following 00 or 01 ending one cohort's life be the number born into the next cohort. Populations constructed in this way showed prolonged existence with total population numbers fluctuating about a mean size and with long-term growth rate (r) , 0. The populations' birth rates and growth rates and the females' per capita fecundity decreased significantly with population size, whereas the death rates showed no significant relationship to population size. These results indicate that age-structured populations can persist for long periods of time with long-term growth rates of zero in the absence of negative-feedback loops between a population's present or prior density and its birth rate, growth rate, and fecundity, contrary to the assumption of density-dependent regulation hypotheses. Thus, a long-term growth rate of zero found in natural populations need not indicate that a population's numbers are regulated by density-dependent factors. [source]


Habitat heterogeneity affects population growth in goshawk Accipiter gentilis

JOURNAL OF ANIMAL ECOLOGY, Issue 2 2001
Oliver Krüger
Summary 1The concept of site-dependent population regulation combines the ideas of Ideal Free Distribution-type of habitat settlement and density dependence in a vital rate mediated by habitat heterogeneity. The latter is also known as habitat heterogeneity hypothesis. Site-dependent population regulation hypothesis predicts that increasing population density should lead to inhabitation of increasingly poor territories and decreasing per capita population growth rate. An alternative mechanism for population regulation in a territorial breeding system is interference competition. However, this would be expected to cause a more even decrease in individual success with increasing density than site-dependent regulation. 2We tested these ideas using long-term (1975,99) population data from a goshawk Accipiter gentilis population in Eastern Westphalia, Germany. 3Goshawk territory occupancy patterns and reproduction parameters support predictions of site-dependent population regulation: territories that were occupied more often and earlier had a higher mean brood size. Fecundity did not decrease with increasing density in best territories. 4Using time-series modelling, we also showed that the most parsimonious model explaining per capita population growth rate included annual mean habitat quality, weather during the chick rearing and autumn period and density as variables. This model explained 63% of the variation in per capita growth rate. The need for including habitat quality in the time-series model provides further support for the idea of site-dependent population regulation in goshawk. [source]


The relationship between socio-sexual behavior and salivary cortisol in bonobos: tests of the tension regulation hypothesis

AMERICAN JOURNAL OF PRIMATOLOGY, Issue 3 2009
Gottfried Hohmann
Abstract Bonobos are known for their pacifistic behavior and their large repertoire of behaviors that are thought to serve conflict resolution. One is an unusual form of ventro-ventral mounting that facilitates genital contacts (GC). Various hypotheses have been proposed to explain its function. In this study we tested predictions of the tension regulation hypothesis using salivary cortisol as a marker for social stress. The results indicate a temporal relationship between GC and cortisol levels. Compared with baseline data and matched samples of unrestricted food access, rates of GC increased when access to food sources was restricted. Cortisol levels were highest when access to food was constrained. However, because the behavioral and hormonal responses occurred when viewing the stimulus at a distance and preceded the physical presence of the stimulus, we conclude that the anticipation of a competitive situation was sufficient to induce social stress. Contrary to our prediction, targets of aggression did not have higher rates of GC nor did they solicit GC more often than others. Furthermore, higher GC rates did not correlate with a more pronounced decrease in cortisol levels. Not all results obtained in this study supported the predictions concerning the regulatory function of GC on social tension and further research is needed to explore this question. However, the results indicate that the anticipation of competition may be sufficient to induce a costly physiological response, and that high levels of resource competition may have lasting effects on physical stress and stress management. Am. J. Primatol. 71:223,232, 2009. © 2008 Wiley-Liss, Inc. [source]