| 1. |
- Andersson, Staffan, 1959, et al.
(författare)
-
Multiple receivers, multiple ornaments, and a trade-off between agonistic and epigamic signaling in a widowbird.
- 2002
-
Ingår i: The American naturalist. - : University of Chicago Press. - 1537-5323 .- 0003-0147. ; 160:5, s. 683-91
-
Tidskriftsartikel (refereegranskat)abstract
- Sexual displays often involve several different ornamental traits. Yet most indicator models of sexual selection based on a single receiver (usually a choosy female) find that multiple handicap signals should be unstable. Here we study reasons for this contradiction, analyzing signal function, signal content, and trade-offs between signals in the polygynous red-collared widowbird Euplectes ardens. Males have both a long, graduated tail and a red carotenoid collar badge. Territory-holding "residents" have slightly shorter tails than the nonbreeding "floaters," but their carotenoid collars are 40% larger, and they have (on the basis of reflectance spectrometry and objective colorimetry) a 23-nm more long-wave ("redder") hue than floaters. This corroborates experimental evidence that the red collar is selected by male contest competition, whereas female choice is based almost exclusively on male tail length. Tail length is negatively correlated with the carotenoid signal, which together with body size and condition explains 55% of the variation in tail length. The trade-off in tail length and carotenoid investment is steeper among residents, suggesting an interaction with costs of territory defense. We propose that the "multiple receiver hypothesis" can explain the coexistence of multiple handicap signals. Furthermore, the trade-off between signal expressions might contribute to the inverse relation between nuptial tail elongation and coloration in the genus Euplectes (bishops and widowbirds).
|
|
| 2. |
- Harding, Karin C., 1968, et al.
(författare)
-
A unifying framework for metapopulation dynamics.
- 2002
-
Ingår i: The American Naturalist. - : University of Chicago Press. - 1537-5323 .- 0003-0147. ; 160:2, s. 173-185
-
Tidskriftsartikel (refereegranskat)abstract
- Many biologically important processes, such as genetic differentiation, the spread of disease, and population stability, are affected by the (natural or enforced) subdivision of populations into networks of smaller, partly isolated, subunits. Such "metapopulations" can have extremely complex dynamics. We present a new general model that uses only two functions to capture, at the metapopulation scale, the main behavior of metapopulations. We show how complex, structured metapopulation models can be translated into our generalized framework. The metapopulation dynamics arising from some important biological processes are illustrated: the rescue effect, the Allee effect, and what we term the "antirescue effect." The antirescue effect captures instances where high migration rates are deleterious to population persistence, a phenomenon that has been largely ignored in metapopulation conservation theory. Management regimes that ignore a significant antirescue effect will be inadequate and may actually increase extinction risk. Further, consequences of territoriality and conspecific attraction on metapopulation-level dynamics are investigated. The new, simplified framework can incorporate knowledge from epidemiology, genetics, and population biology in a phenomenological way. It opens up new possibilities to identify and analyze the factors that are important for the evolution and persistence of the many spatially subdivided species.
|
|
| 3. |
- Persson, Anders, et al.
(författare)
-
Effects of enrichment on simple aquatic food webs
- 2001
-
Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 157:6, s. 654-669
-
Tidskriftsartikel (refereegranskat)abstract
- Simple models, based on Lotka-Volterra types of interactions between predator and prey, predict that enrichment will have a destabilizing effect on populations and that equilibrium population densities will change at the top trophic level and every second level below. We experimentally tested these predictions in three aquatic food web configurations subjected to either high or low nutrient additions. The results were structured by viewing the systems as either food chains or webs and showed that trophic level biomass increased with enrichment, which contradicts food chain theory. However, within each trophic level, food web configuration affected the extent to which different functional groups responded to enrichment. By dividing trophic levels into functional groups, based on vulnerability to consumption, we were able to identify significant effects that were obscured when systems were viewed as food chains. The results support the prediction that invulnerable prey may stabilize trophic-level dynamics by replacing other, more vulnerable prey. Furthermore, the vulnerable prey, such as Daphnia and edible algae, responded as predicted by the paradox of enrichment hypothesis; that is, variability in population density increased with enrichment. Hence, by describing ecosystems as a matrix of food web interactions, and by recognizing the interplay between interspecific competition and predation, a more complete description of the ecosystem function was obtained compared to when species were placed into distinct trophic levels.
|
|
| 4. |
- Strauss, S Y, et al.
(författare)
-
Effects of foliar herbivory by insects on the fitness of Raphanus raphanistrum : damage can increase male fitness.
- 2001
-
Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 158:5, s. 496-504
-
Tidskriftsartikel (refereegranskat)abstract
- Generally, effects of herbivory on plant fitness have been measured in terms of female reproductive success (seed production). However, male plant fitness, defined as the number of seeds sired by pollen, contributes half of the genes to the next generation and is therefore crucial to the evolution of natural plant populations. This is the first study to examine effects of insect herbivory on both male and female plant reproductive success. Through controlled field and greenhouse experiments and genetic paternity analysis, we found that foliar damage by insects caused a range of responses by plants. In one environment, damaged plants had greater success as male parents than undamaged plants. Neither effects on pollen competitive ability nor pollinator visitation patterns could explain the greater siring success of these damaged plants. Success of damaged plants as male parents appeared to be due primarily to changes in allocation to flowers versus seeds after damage. Damaged plants produced more flowers early in the season, but not more seeds, than undamaged plants. Based on total seed production, male fitness measures from the first third of the season, and flower production, we estimated that damaged and undamaged plants had equal total reproductive success at the end of the season in this environment. In a second, richer environment, damaged and undamaged plants had equal male and female plant fitness, and no traits differed significantly between the treatments. Equal total reproductive success may not be ecologically or evolutionarily equivalent if it is achieved differentially through male versus female fitness. Genes from damaged plants dispersed through pollen may escape attack from herbivores, if such attack is correlated spatially from year to year.
|
|
| 5. |
- Svensson, Erik, et al.
(författare)
-
Spatial scale and temporal component of selection in side-blotched lizards
- 2004
-
Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 163:5, s. 726-734
-
Tidskriftsartikel (refereegranskat)abstract
- Spatial variation in selection has long been recognized as promoting population divergence and in maintaining genetic polymorphisms, but selection at a fine spatial scale is seldom measured directly. We analyzed spatial and temporal variation in selective regimes on egg size using long-term population data of the side-blotched lizard ( Uta stansburiana). Juvenile survival rates varied between years at a small spatial scale that was reflected as a strong interaction between the local neighborhood level and year. Spatially and temporally variable selection acted jointly on egg mass, which presumably would facilitate the maintenance of high additive genetic variance for this trait. Local selection gradients calculated at the neighborhood level were significantly correlated with the annual global selection gradients calculated at the metapopulation level. However, there was substantial variance in these local selective regimes, which suggests that strong local selection could go undetected if the analysis was limited to the global level. We also investigated the degree of spatial synchronization among outcrop in local selection gradients. The degree of synchrony was higher among later-clutch hatchlings than among first-clutch hatchlings, and we suggest that more intense density- and frequency-dependent selection on egg size later in the season is responsible for this effect.
|
|
| 6. |
- Brodin, Anders, et al.
(författare)
-
The effect of dominance on food hoarding: A game theoretical model
- 2001
-
Ingår i: American Naturalist. - 0003-0147. ; 157:1, s. 66-75
-
Tidskriftsartikel (refereegranskat)abstract
- Many food hoarding animals live in small groups structured by rank. The presence of conspecifics in the hoarding area increases the risk of losing stored supplies. The possibility of stealing from others depends on a forager's rank in the group. Highly ranked individuals can steal from subordinates and also protect their own caches. Since storing incurs both costs and benefits, the optimal hoarding investment will differ between individuals of different rank. In a game theoretical model, we investigate how dominant and subordinate individuals should optimize their hoarding effort. Our model imagines animals that are large-scale hoarders in autumn and dependent on stored supplies for winter survival. Many examples can be found in the bird families Paridae and Corvidae, but the model can be used for any hoarding species that forage in groups. Predictions from the model are as follows: First, subordinates should store more than dominants, but in a predictable environment, this difference will decrease as the environment gets harsher. Under harsh conditions, dominants should store almost as much as subordinates and, later, spend almost as much time retrieving their own caches as subordinates. Second, if on the other hand, bad winter conditions were not expected when storing, dominants should spend more time pilfering caches from subordinates. Third, in populations that are highly dependent on stored supplies, dominants should store relatively more than in populations that are less dependent on stored supplies. Fourth, harsher environments will favor hoarding. And finally, if dominant individuals store, it implies that hoarders have a selfish recovery advantage over conspecific pilferers.
|
|
| 7. |
- Härdling, Roger, et al.
(författare)
-
Dynamics of the caring family
- 2003
-
Ingår i: American Naturalist. - 0003-0147. ; 161:3, s. 395-412
-
Tidskriftsartikel (refereegranskat)abstract
- When several individuals simultaneously provide for offspring, as in families, the effort of any one individual will depend on the efforts of the other family members. This conflict of interest among family members is made more complicated by their relatedness because relatives share genetic interest to some degree. The conflict resolution will also be influenced by the differences in reproductive value between breeders and helpers. Here, we calculate evolutionarily stable provisioning efforts in families with up to two helpers. We explicitly consider that the behavioral choices are made in a life-history context, and we also consider how group sizes change dynamically; this affects, for example, average relatedness among group members. We assume two different scenarios: intact families in which the breeder is 100% monogamous and stepfamilies in which the breeder shifts mate between breeding events. The average relatedness among family members is allowed to evolve in concert with changes in provisioning effort. Our model shows that an individual's provisioning effort is not easy to predict from either its relatedness to the offspring or its reproductive value. Instead, it is necessary to consider the inclusive fitness effect of provisioning, which is determined by a combination of relatedness, reproductive value, and the reproductive value of the offspring.
|
|
| 8. |
- Härdling, Roger, et al.
(författare)
-
Priority versus brute force: When should males begin guarding resources?
- 2004
-
Ingår i: American Naturalist. - 0003-0147. ; 163:2, s. 240-252
-
Tidskriftsartikel (refereegranskat)abstract
- When should males begin guarding a resource when both resources and guarders vary in quality? This general problem applies, for example, to migrant birds occupying territories in the spring and to precopula in crustaceans where males grab females before they molt and become receptive. Previous work has produced conflicting predictions. Theory on migrant birds predicts that the strongest competitors should often arrive first, whereas some models of mate guarding have predicted that the strongest competitors wait and then simply usurp a female from a weaker competitor. We build a general model of resource guarding that allows varying the ease with which takeovers occur. The model is phrased in terms of mate-guarding crustaceans, but the same logic can be applied to other forms of resource acquisition where priority plays a role but takeovers might be possible too. The race to secure breeding positions can lead to strong competitors (large males) taking females earliest, even though this means accepting a lower-quality female. Paradoxically, this means that small males, which have fewer breeding opportunities, are more choosy than larger ones. Such solutions are found when takeovers are impossible. The easier the takeovers and the higher the rate of finding guarded resources, the more likely are solutions where guarding durations are short, where strong competitors begin guarding only just before breeding, and where they do this by usurping the resource. The relationship between an individual's competitive ability and its timing of resource acquisition can also be nonlinear if takeovers are moderately common; if this is the case, then males of intermediate size guard the longest.
|
|
| 9. |
- Jonzén, Niclas, et al.
(författare)
-
A theory of stochastic harvesting in stochastic environments
- 2002
-
Ingår i: American Naturalist. - 0003-0147. ; 159:5, s. 427-437
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate how model populations respond to stochastic harvesting in a stochastic environment. In particular, we show that the effects of variable harvesting on the variance in population density and yield depend critically on the autocorrelation of environmental noise and on whether the endogenous dynamics of the population display over- or undercompensation to density. These factors interact in complicated ways; harvesting shifts the slope of the renewal function, and the net effect of this shift will depend on the sign and magnitude of the other influences. For example, when environmental noise exhibits a positive auto correlation, the relative importance of a variable harvest to the variance in density increases with overcompensation but decreases with undercompensation. For a fixed harvesting level, an increasing level of autocorrelation in environmental noise will decrease the relative variation in population density when overcompensation would otherwise occur. These and other intricate interactions have important ramifications for the interpretation of time series data when no prior knowledge of demographic or environmental details exists, These effects are important whenever the harvesting rate is sufficiently high or variable, conditions likely to occur in many systems, whether the harvesting is caused by commercial exploitation or by any other strong agent of density-independent mortality.
|
|
| 10. |
- Jonzén, Niclas, et al.
(författare)
-
Habitat selection and population regulation in temporally fluctuating environments
- 2004
-
Ingår i: American Naturalist. - 0003-0147. ; 164:4, s. 103-114
-
Tidskriftsartikel (refereegranskat)abstract
- Understanding and predicting the distribution of organisms in heterogeneous environments lies at the heart of ecology, and the theory of density-dependent habitat selection (DDHS) provides ecologists with an inferential framework linking evolution and population dynamics. Current theory does not allow for temporal variation in habitat quality, a serious limitation when confronted with real ecological systems. We develop both a stochastic equivalent of the ideal free distribution to study how spatial patterns of habitat use depend on the magnitude and spatial correlation of environmental stochasticity and also a stochastic habitat selection rule. The emerging patterns are confronted with deterministic predictions based on isodar analysis, an established empirical approach to the analysis of habitat selection patterns. Our simulations highlight some consistent patterns of habitat use, indicating that it is possible to make inferences about the habitat selection process based on observed patterns of habitat use. However, isodar analysis gives results that are contingent on the magnitude and spatial correlation of environmental stochasticity. Hence, DDHS is better revealed by a measure of habitat selectivity than by empirical isodars. The detection of DDHS is but a small component of isodar theory, which remains an important conceptual framework for linking evolutionary strategies in behavior and population dynamics.
|
|
