1,576 research outputs found
Lactation patterns of pinnipeds are not explained by optimization of maternal energy delivery rates
No full textTrillmich F, Weissing FJ. Lactation patterns of pinnipeds are not explained by optimization of maternal energy delivery rates. BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY. 2006;60(2):137-149.Within pinnipeds, phocids and otariids show differing maternal care. strategies. Phocids rear young out of body stores in a yearly cycle with a single stay ashore when the mother fasts while lactating, whereas otariids provision their young by repeated foraging trips to sea alternating with brief stays ashore where they suckle their young. In a previous optimality model, these differences have been interpreted as adaptations based on differing energy requirements of large (phocid) and smaller (otariid) species, and the time budget of the large elephant and the much smaller Antarctic fur seal were correctly predicted. Our refined model-extended to pinniped species of all sizes-predicts lactation strategies to shift from attendance cycles to 1-year cycles with increasing body mass and provides an explanation for the finding that phocid pups are weaned at lower relative mass than otariid pups. However, other predictions do not correspond to empirical findings. In particular, the model does not explain the behavior of large otariids and small phocids. Thus, maternal metabolic requirements alone appear insufficient to explain observed lactation patterns. In the light of our results, we discuss more generally the scope and limitations of optimality models when applied in a comparative framework to a group of related species
Selection and Segregation Distortion in a Sex-Differentiated Population
No full textthis paper, we will focus on the interaction of selection and segregation distortion, which is harder to analyze and less well understood (e.g., Taylor and Jonker, 1978; Weissing, 1991; Hofbauer and Sigmund, 1998). In this case, w ij should be interpreted as the fitness of an individual of genotype A i A j viewed from the perspective of allele A i . Hence, our model explicitly takes the point of view of the allele instead of that of the genotyp
Genetic versus phenotypic models of selection: Can genetics be neglected in a long-term perspective?
Get PDFGame theoretical concepts in evolutionary biology have been criticized by populations geneticists, because they neglect such crucial aspects as the mating system-or the mode of inheritance. In fact, the dynamics of natural selection does not necessarily lead to a fitness maximum or an ESS if genetic constraints are taken into account. Yet, it may be premature to conclude that game theoretical concepts do not have a dynamical justification. The new paradigm of long-term evolution postulates that genetic constraints, which may be dominant in a short-term perspective, will in the long run disappear in the face of the ongoing influx of mutations. Two basic results (see Hammerstein; this issue) seem to reconcile the dynamical approach of long-term population genetics with the static approach of evolutionary game theory: (1) only populations at local fitness optima (Nash strategies) can be long-term stable; and (2) in monomorphic populations, evolutionary stability is necessary and sufficient to ensure long-term dynamic stability. The present paper has a double purpose. On the one hand, it is demonstrated by fairly general arguments that the scope of the results mentioned above extends to non-linear frequency dependent selection, to multiple loci, and to quite general mating systems. On the other hand, some limitations of the theory of long-term evolution will also be stressed: (1) there is little hope for a game theoretical characterization of stability in polymorphic populations; (2) many interesting systems do not admit long-term stable equilibria; and (3) even if a long-term stable equilibrium exists, it is not at all clear whether and how it is attainable by a series of gene substitution event
Variation in habitat choice and delayed reproduction: Adaptive queuing strategies or individual quality differences?
Get PDFIn most species, some individuals delay reproduction or occupy inferior breeding positions. The queue hypothesis tries to explain both patterns by proposing that individuals strategically delay breeding (queue) to acquire better breeding or social positions. In 1995, Ens, Weissing, and Drent addressed evolutionarily stable queuing strategies in situations with habitat heterogeneity. However, their model did not consider the non - mutually exclusive individual quality hypothesis, which suggests that some individuals delay breeding or occupy inferior breeding positions because they are poor competitors. Here we extend their model with individual differences in competitive abilities, which are probably plentiful in nature. We show that including even the smallest competitive asymmetries will result in individuals using queuing strategies completely different from those in models that assume equal competitors. Subsequently, we investigate how well our models can explain settleme! nt patterns in the wild, using a long-term study on oystercatchers. This long-lived shorebird exhibits strong variation in age of first reproduction and territory quality. We show that only models that include competitive asymmetries can explain why oystercatchers' settlement patterns depend on natal origin. We conclude that predictions from queuing models are very sensitive to assumptions about competitive asymmetries, while detecting such differences in the wild is often problematic.
Constraints on Allele size at microsatellite loci: Implications for genetic differentiation
No full textMicrosatellites are promising genetic markers for studying the demographic structure and phylogenetic history of populations. We present theoretical arguments indicating that the usefulness of microsatellite data for these purposes may be limited to a short time perspective and to relatively small populations. The evolution of selectively neutral markers is governed by the interaction of mutation and random genetic drift. Mutation pressure has the inherent tendency to shift different populations to the same distribution of alleles. Hence, mutation pressure is a homogenizing force, and population divergence is caused by random genetic drift. In case of allozymes or sequence data, the diversifying effect of drift is typically orders of magnitude larger than the homogenizing effect of mutation pressure. By a simple model, we demonstrate that the situation may be different for microsatellites where mutation rates are high and the range of alleles is limited. with the help of computer simulations, we investigate to what extent genetic distance measures applied to microsatellite data can nevertheless yield useful estimators for phylogenetic relationships or demographic parameters. We show that predictions based on microsatellite data are quite reliable in small populations, but that already in moderately sized populations the danger of misinterpretation is substantial
Towards a unified theory of cooperative breeding: The role of ecology and life history re-examined
Get PDFWe present quantitative models that unify several adaptive hypotheses for the evolution of cooperative breeding in a single framework: the ecological constraints hypothesis, the life-history hypothesis and the benefits-of-philopatry hypothesis. Our goal is to explain interspecific variation in the occurrence of cooperative breeding in terms of interspecific variation in life-history traits and ecological conditions. We analyse two models, according to whether or not helpers can inherit their parents’ territory. Major results are (i) territory inheritance always promotes cooperative breeding; (ii) if territories are not inherited, neither ecological constraints nor variation in life-history traits predict interspecific variation in cooperative breeding; and (iii) if territories are inherited, the mechanism of density regulation is crucial in determining which factors promote cooperative breeding. If density dependence acts on the probability to obtain a free territory or on the survival of dispersers, variation in ecological constraints cannot explain variation in cooperative breeding. Lower adult mortality favours helping, not because it reduces the availability of free territories, but because it enhances the direct benefits of helpers. If density dependence acts on fecundity, lower probability of obtaining a free territory and lower survival of dispersers promote cooperative breeding. In this case, lower adult mortality works against the evolution of helping. We suggest that the difference between birds and social insects in the covariance between cooperative breeding and life-history traits is due to different mechanisms of density regulation that operate in these taxa, and we explain how natural selection on habitat choice might have caused these different mechanisms to operate
Sperm competition and sex allocation in simultaneous hermaphrodites: A new look at Charnov's invariance principle
No full textRecently, Charnov (1996) investigated the consequences of sperm competition for optimal sex allocation in simultaneous hermaphrodites. Charnov argued that the optimal sex allocation strategy can be derived on the basis of the 'sperm displacement rule'; that is, the function describing the relationship between sperm production and sperm displacement. Based on three specific examples of such sperm displacement rules, Charnov claimed that the details of the relationship between ejaculate volume and sperm displacement have only a minor effect on the optimal sex allocation strategy. We demonstrate that this 'invariance principle' is less general than suggested. The optimal sex allocation strategy as a function of the dimensionless quantity delta (ratio of maximum sperm volume to sperm storage volume) can have a wide variety of shapes. This is because Charnov's results depend crucially on two assumptions of questionable generality: diminishing displacement with investment in sperm and linear fitness returns with investment in eggs. We argue that deeper insights into optimal sex allocation are obtained if the allocation decision is partitioned into multiple components. Using this approach, we find a novel invariance principle: if egg survival only depends on the investment per egg (and not on clutch size), then the shape of this relationship has no effect whatsoever on optimal allocation to eggs versus sperm
Competition for nutrients and light in a mixed water column: a theoretical analysis
Get PDFInteractions between nutrient limitation and light limitation are fundamental for the dynamics and structure of phytoplankton communities. We investigate a model that predicts the outcome of competition for nutrients and light in a mixed water column on the basis of monoculture characteristics. Growth in monoculture leads to a steady state. The nutrient availability and light penetration in this steady state characterize the minimal resource requirements of a species. These minimal requirements not only determine monoculture growth but also the outcome of competition. We show that competition for nutrients and light can be investigated by means of a graphical isocline approach. In contrast to earlier resource-based approaches, our model predicts that it is not only the ratio of nutrient supply to light supply that matters for the outcome of competition but also their absolute supply rates. It is even possible that a species that competes successfully when there is a high or low light supply is displaced when the light supply is intermediate. Factors such as mixing depth and background turbidity also affect the composition of phytoplankton communities. Still. our model predicts that at most two species can stably coexist in a mixed water column. Hence, the spatial heterogeneity imposed by a light gradient is nor sufficient to solve Hutchinson's paradox of the plankton
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