| 41. |
- Knape, Jonas, et al.
(författare)
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An analysis of hatching success in the great reed warbler Acrocephalus arundinaceus
- 2008
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; :117, s. 430-438
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Tidskriftsartikel (refereegranskat)abstract
- Hatching success is a potentially important fitness component for avian species. Previous studies of hatching success in natural populations have primarily focused on effects of inbreeding but a general understanding of variation in hatching success is lacking. We analyse data on hatching success in a population of great reed warblers Acrocephalus arundinaceus in Lake Kvismaren in south central Sweden. The effects of a range of covariates, including three measures of inbreeding as well as effects of classifications in the data (such as identities of individuals), on hatching success are analysed simultaneously. This is done by means of fitting Bayesian binomial mixed models using Markov chain Monte Carlo methods. Using random effects for each individual parent we check for unexplained variation in hatching success among male and female individuals and compare it to effects of covariates such as degree of inbreeding. Model selection showed that there was a significant amount of unexplained variation in hatching probability between females. This was manifested by a few females laying eggs with a substantially lower hatching success than the majority of the females. The deviations were of the same order of magnitude as the significant effect of parent relatedness on hatching success. Whereas the negative effect of parent relatedness on hatchability is an expression of inbreeding, the female individual effect is not due to inbreeding and could reflect maternal effects, that females differ in fertilisation and/or incubation ability, or an over representation of genetic components from the female acting on the early developing embryo.
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| 42. |
- Kvist, Anders, et al.
(författare)
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Gluttony in migratory waders - unprecedented energy assimilation rates in vertebrates
- 2003
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 103:2, s. 397-402
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Tidskriftsartikel (refereegranskat)abstract
- Maximum energy assimilation rate has been implicated as a constraint on maximal sustained energy expenditure, on biomass production, and in various behavioural and life history models. Data on the upper limit to energy assimilation rate are scarce, and the factors that set the limit remain poorly known. We studied migratory waders in captivity, given unlimited food supply around the clock. Many of these waders assimilated energy at rates of seven to ten times basal metabolism, exceeding maximum rates reported for vertebrates during periods of high energy demand, for example during reproduction and in extreme cold. One factor allowing the high energy assimilation rates may be that much of the assimilated energy is stored and not concomitantly expended by muscles or other organs. The remarkable digestive capacity in waders is probably an adaptation to long and rapid migrations, putting a premium on high energy deposition rates. The upper limit to daily energy assimilation in vertebrates is clearly higher than hitherto believed, and food availability, total daily feeding time and, possibly, the fate of assimilated energy may be important factors to take into account when estimating limits to energy budgets in animals.
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| 43. |
- Lankinen, Åsa, et al.
(författare)
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Allocation to pollen competitive ability versus seed production in Viola tricoloras an effect of plant size, soil nutrients and presence of a root competitor
- 2012
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Ingår i: Oikos. - : John Wiley & Sons. - 0030-1299 .- 1600-0706. ; 122:5, s. 779-789
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Tidskriftsartikel (refereegranskat)abstract
- In hermaphroditic plants, the effect of a social environment on sex allocation has not been studied to our knowledge, while in hermaphroditic animals such effects are known to be common. In recent years, studies on root competition beyond the effects of nutrients have shown that plants can respond to their conspecific root competitors (social environment), making it interesting to ask if these effects could also influence sex allocation in addition to more commonly studied factors, such as plant size or resources. In this study on hermaphroditic Viola tricolor, we investigated how plant size, soil nutrients and presence of a root competitor influenced allocation to pollen competitive ability versus seed production, i.e. male and female reproductive functions. We allowed plants to grow in pairs with partly intermingled or separate roots in the same amount of soil. In additional treatments with intermingled roots (as part of the same experiment) one of the two competitors was given combinations of nitrogen (N), phosphorous (P) and micro nutrients. We found that pollen performance but not seed production increased when plants were in contact in the soil. Additionally, pollen performance was negatively correlated to plant size across fertilisation treatments. For seed production, the opposite relation to plant size was seen, indicating that large, fertilized plants invest relatively more in the female function. In conclusion, in violets, sex allocation appears to be size-dependent and influenced by both the presence of a root competitor and by nutrients. These results suggest that social environment can influence sex allocation in plants as well as in animals, indicating that such effects are important to consider in sex allocation studies across taxa.
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| 44. |
- Lankinen, Åsa, et al.
(författare)
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Evolution of pistil length as a choice mechanism for pollen quality
- 2001
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 92:1, s. 81-90
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Tidskriftsartikel (refereegranskat)abstract
- During the fertilisation process in plants, pollen tube growth rate may be selected as a trait important in male to male competition. Since female morphology provides the necessary selective arena for such competition. we investigate if sexual selection theory can be used to explain the evolution of pistil length as a female choice mechanism. This choice is performed by direct interference with male to male competition. Furthermore, the sessile nature of plants limits the number of mates a female can choose between, which could limit the benefit a female can gain from distinguishing between donors. To mirror these circumstances, we model a situation when there are only two competitors at a time. Using a game theoretical approach we show that if pollen tube growth rate can be used as an indication of heritable quality, pistil length can be selected in response to variation of this trait. We further find that length of the pistil affects selection of pollen tube growth rate. Thus female preference and male competitive ability co-evolve, but this does not necessarily lead to a positive relationship between the two. Under certain circumstances we find a negative relation instead. Given realistic differences in male quality, the model indicates that there is a potential for evolution of female morphology as a choice mechanism for pollen quality.
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| 45. |
- Lankinen, Åsa, et al.
(författare)
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The effect of pollen competition on maintenance of variation in fertilisation ability
- 2001
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 93:3, s. 459-469
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Tidskriftsartikel (refereegranskat)abstract
- Pollen competition in the pistil does not only give flowering plants the possibility to reduce inbreeding but also provides an opportunity for selection of pollen traits that increase male reproductive success. An objection to the existence of selection on pollen competitive ability is that individual variation should quickly vanish if selection is strong. A balance between selection for local adaptation of sporophytes within sites and pollen flow between sites could maintain variation in pollen competitive ability. A prerequisite is that variation in male competitive ability is condition dependent, i.e., influenced by sporophytic adaptation to a parch. This further means that selection on pollen competitive ability can occur both directly on the gamethophytic level and indirectly on the sporophytic level. Our dynamic model shows that maintenance of variation in male competitive ability is more probable when: differences in pollen competitive ability influence male fitness, i.e., in cases with pollen competition, than when differences in this trait only is a side effect of selection for more viable individuals. Since there is a connection between the gamethophytic and sporophytic life-phases, the incidence of pollen competition between donors should make it more probable that variability also in sporophyte fitness is preserved.
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| 46. |
- Lardner, Björn
(författare)
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Morphological and life history responses to predators in larvae of seven anurans
- 2000
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Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 88:1, s. 169-180
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Tidskriftsartikel (refereegranskat)abstract
- Amphibian larvae often face two major sources of mortality: pond desiccation and predation. Tadpoles of seven anuran species with different preferences for type of breeding habitat, on a hydroperiod scale, were tested for responses to the presence of predators by raising them experimentally in the presence and absence of a separately caged invertebrate predator that was fed on conspecific tadpoles. The species typically breeding in temporary or semi-permanent ponds (Rana temporaria, Rana arvalis, Rana dalmatina and Hyla arborea) - where invertebrate predator populations are predicted to vary considerably spatiotemporally - all showed marked induced increases in tail fin depth in response to predator presence. These species also tended to respond by reduced growth rates. The representative of the most ephemeral habitats, Bufo calamita, did not respond in any of these traits. Its congeneric, Bufo bufo, a toxic inhabitant of permanent ponds and lakes, tended to respond to predator presence by reducing its growth rate, though not by a tail depth increase. I argue that the rather poor swimming performance in Bufo tadpoles may opt for defences other than locomotor ability. The palatable, permanent pond species Pelobates fuscus did not alter either its growth rate or tail morphology. Possible explanations for this result are discussed.
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| 47. |
- Leps, J, et al.
(författare)
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Separating the chance effect from other diversity effects in the functioning of plant communities
- 2001
-
Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 92:1, s. 123-134
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Tidskriftsartikel (refereegranskat)abstract
- The effect of plant species diversity on productivity and competitive ability was studied in an experiment carried out simultaneously in five European countries: Czech Republic (CZ), the Netherlands (NL), Sweden (SE), Spain (SP), and United Kingdom (UK). The aim was to separate the 'chance' or 'sampling effect' (increasing the number of sown species increases the probability that a species able 'to do a job' will be included) from the complementarity effect (species-rich communities are better able to exploit resources and to take care of ecosystem functions than species-poor communities). In the experiment, low diversity (LD) and high diversity (HD) mixtures of grassland species were sown into fields taken out of arable cultivation. The HD mixture consisted of five grass species, five legumes and five other forbs. The LD mixtures consisted of two grasses, one legume and one other forb, with different plant species combinations in each replicate block. The design of the experiment was constructed in such a way that the total number of seeds of each species over all the replications was exactly the same in HD and LD treatments, and the total number of grass seeds, leguminous seeds and other forb seeds were the same in both LD and HD. The responses measured were the total above-ground biomass las a measure of productivity) and the average number of naturally establishing species in a plot las a measure of the competitive ability of the mixture), both measured in the third year of the experiment. The results show that, on average, the HD plots performed better (i.e., attained higher biomass, had better weed suppression), but that the best LD mixture was as good as the best HD mixture. On the contrary, the worst LD mixture was always less successful than the worst HD replicate. The performance of particular species in the HD mixtures was a good predictor of the success of a certain species combination in a LD mixture (explaining 61% of variability between particular LD mixtures). In all sites, the LD mixture composed of species which were the most abundant in HD mixtures was as efficient in suppressing weeds as the HD mixture itself. It is argued that the performance of a species assemblage is influenced mostly by the identity of species and the diversity effect is mainly due to the 'chance' or 'sampling' effect with increasing number of species the probability that an important species will be included in the mixture increases. Caution is urged in interpreting experiments with manipulated diversity and the possible limitations of such experiments are discussed.
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| 48. |
- Linden, Andreas, et al.
(författare)
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Estimating environmental effects on population dynamics: consequences of observation error
- 2009
-
Ingår i: Oikos. - : Wiley. - 1600-0706 .- 0030-1299. ; 118:5, s. 675-680
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Tidskriftsartikel (refereegranskat)abstract
- Within the paradigm of population dynamics a central task is to identify environmental factors affecting population change and to estimate the strength of these effects. We here investigate the impact of observation errors in measurements of population densities on estimates of environmental effects. Adding observation errors may change the autocorrelation of a population time series with potential consequences for estimates of effects of autocorrelated environmental covariates. Using Monte Carlo simulations, we compare the performance of maximum likelihood estimates from three stochastic versions of the Gompertz model (log-linear first order autoregressive model), assuming 1) process error only, 2) observation error only, and 3) both process and observation error (the linear state-space model on log-scale). We also simulated population dynamics using the Ricker model, and evaluated the corresponding maximum likelihood estimates for process error models. When there is observation error in the data and the considered environmental variable is strongly autocorrelated, its estimated effect is likely to be biased when using process error models. The environmental effect is overestimated when the sign of the autocorrelations of the intrinsic dynamics and the environment are the same and underestimated when the signs differ. With non-autocorrelated environmental covariates, process error models produce fairly exact point estimates as well as reliable confidence intervals for environmental effects. In all scenarios, observation error models produce unbiased estimates with reasonable precision, but confidence intervals derived from the likelihood profiles are far too optimistic if there is process error present. The safest approach is to use state-space models in presence of observation error. These are factors worthwhile to consider when interpreting earlier empirical results on population time series, and in future studies, we recommend choosing carefully the modelling approach with respect to intrinsic population dynamics and covariate autocorrelation.
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| 49. |
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| 50. |
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