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121.
Early warning signals (EWS) of regime shifts are challenging in cases where the true natural data-generating process is uncertain. Nonparametric drift-diffusion-jump models address this problem by fitting a general model that can approximate a wide range of data-generating processes. Drift measures the local rate of change. Diffusion measures relatively small shocks that occur at each time step. Jumps are large intermittent shocks. Total variance combines the contributions of diffusion and jumps. Nonparametric methods are well suited to emerging technology for automated, high-frequency sensors. Total variance is the most precisely measured indicator. Jump intensity appears to be a useful EWS. Estimates of the drift are highly uncertain unless long time series with many regime shifts are available. EWS computed from drift estimates (such as autocorrelation coefficients or return rates) have low precision and should be used with caution. Nonetheless, in the current state of knowledge, it is premature to disregard any potential EWS. 相似文献
122.
Dubuc C Muniz L Heistermann M Engelhardt A Widdig A 《Behavioral ecology and sociobiology》2011,65(8):1615-1627
In mammals, when females are clumped in space, male access to receptive females is usually determined by a dominance hierarchy
based on fighting ability. In polygynandrous primates, as opposed to most mammalian species, the strength of the relationship
between male social status and reproductive success varies greatly. It has been proposed that the degree to which paternity
is determined by male rank decreases with increasing female reproductive synchrony. The priority-of-access model (PoA) predicts
male reproductive success based on female synchrony and male dominance rank. To date, most tests of the PoA using paternity
data involved nonseasonally breeding species. Here, we examine whether the PoA explains the relatively low reproductive skew
in relation to dominance rank reported in the rhesus macaque, a strictly seasonal species. We collected behavioral, genetic,
and hormonal data on one group of the free-ranging population on Cayo Santiago (Puerto Rico) for 2 years. The PoA correctly
predicted the steepness of male reproductive skew, but not its relationship to male dominance: the most successful sire, fathering
one third of the infants, was high but not top ranking. In contrast, mating success was not significantly skewed, suggesting
that other mechanisms than social status contributed to male reproductive success. Dominance may be less important for paternity
in rhesus macaques than in other primate species because it is reached through queuing rather than contest, leading to alpha
males not necessarily being the strongest or most attractive male. More work is needed to fully elucidate the mechanisms determining
paternity in rhesus macaques. 相似文献
123.
Brose U Jonsson T Berlow EL Warren P Banasek-Richter C Bersier LF Blanchard JL Brey T Carpenter SR Blandenier MF Cushing L Dawah HA Dell T Edwards F Harper-Smith S Jacob U Ledger ME Martinez ND Memmott J Mintenbeck K Pinnegar JK Rall BC Rayner TS Reuman DC Ruess L Ulrich W Williams RJ Woodward G Cohen JE 《Ecology》2006,87(10):2411-2417
It has been suggested that differences in body size between consumer and resource species may have important implications for interaction strengths, population dynamics, and eventually food web structure, function, and evolution. Still, the general distribution of consumer-'resource body-size ratios in real ecosystems, and whether they vary systematically among habitats or broad taxonomic groups, is poorly understood. Using a unique global database on consumer and resource body sizes, we show that the mean body-size ratios of aquatic herbivorous and detritivorous consumers are several orders of magnitude larger than those of carnivorous predators. Carnivorous predator-prey body-size ratios vary across different habitats and predator and prey types (invertebrates, ectotherm, and endotherm vertebrates). Predator-prey body-size ratios are on average significantly higher (1) in freshwater habitats than in marine or terrestrial habitats, (2) for vertebrate than for invertebrate predators, and (3) for invertebrate than for ectotherm vertebrate prey. If recent studies that relate body-size ratios to interaction strengths are general, our results suggest that mean consumer-resource interaction strengths may vary systematically across different habitat categories and consumer types. 相似文献