0000000000129227
AUTHOR
Niclas Jonzén
Coexistence and resource competition.
How large numbers of species coexist on a seemingly limited number of different resources is a classic problem in ecology1, and attempts have been made to solve it experimentally. But we are not convinced that Huisman and Weissing's2 proposal to add non-stationary dynamics in species abundance to the list of possible explanations offers any new insight into this biodiversity enigma.
Density-dependent body growth reduces the potential of marine reserves to enhance yields
1. Some models of marine no-take reserves predict that reserves can enhance fishery yield. However, empirical evidence of this remains inconclusive. One reason for this may be the disregard for density-dependent body growth in most models. Density-dependent body growth links the number and size of individuals, and thus could influence the biomass of fishery yield. 2. We developed an age- and size-structured model of an exploited population and analysed the effect of implementing a no-take reserve of varying size. 3. Protecting part of a population from exploitation in a no-take reserve results in a rapid build-up of biomass inside the reserve because of increased survival. However, when bod…
Population dynamics of the Swedish Ornithological Society
It has recently been recognized that there is declining interest in ornithology among the younger generations. In this paper we analyse the short and long-term dynamics of the Swedish Ornithological Society (SOF) and the Swedish Society for Nature Conservation (SNF) by using analytical tools from population ecology. We first show that the increasing number of SOF and SNF members is not the result of a constant proportion of ornithologists or people interested in nature conservation among a growing Swedish population. Hence, the number of members most likely reflects the true interest in joining organizations such as SOF. We also demonstrate that the growth rate of SOF can be fairly well est…
Harvesting‐induced population fluctuations?
It has recently been shown that damped endogenous dynamics is a common feature in Finnish grouse species; In this paper, we demonstrate that time-variant harvesting may turn damped dynamics to quasi-periodic fluctuations. Exploited populations, e.g. grouse, may therefore fluctuate more than expected if we do not manage to keep the harvest fraction constant over time. However, the harvest fraction of Finnish grouse varies with the phase of the cycle. Such a harvesting strategy could potentially change the periodicity of the fluctuations, as can a threshold harvest strategy where a constant fraction is harvested above a density threshold. The two non-linear harvesting strategies investigated …
The irreducible uncertainty of the demography–environment interaction in ecology
The interpretation of ecological data has been greatly improved by bridging the gap between ecological and statistical models. The major challenge is to separate competing hypotheses concerning demography, or other ecological relationships, and environmental variability (noise). In this paper we demonstrate that this may be an arduous, if not impossible, task. It is the lack of adequate ecological theory, rather than statistical sophistication, which leads to this problem. A reconstruction of underlying ecological processes can only be done if we are certain of either the demographic or the noise model, which is something that can only be achieved by an improved theory of stochastic ecologi…