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641.
Ohlberger J Langangen Ø Edeline E Claessen D Winfield IJ Stenseth NC Vøllestad LA 《Ecology》2011,92(12):2175-2182
Recently developed theoretical models of stage-structured consumer-resource systems have shown that stage-specific biomass overcompensation can arise in response to increased mortality rates. We parameterized a stage-structured population model to simulate the effects of increased adult mortality caused by a pathogen outbreak in the perch (Perca fluviatilis) population of Windermere (UK) in 1976. The model predicts biomass overcompensation by juveniles in response to increased adult mortality due to a shift in food-dependent growth and reproduction rates. Considering cannibalism between life stages in the model reinforces this compensatory response due to the release from predation on juveniles at high mortality rates. These model predictions are matched by our analysis of a 60-year time series of scientific monitoring of Windermere perch, which shows that the pathogen outbreak induced a strong decrease in adult biomass and a corresponding increase in juvenile biomass. Age-specific adult fecundity and size at age were higher after than before the disease outbreak, suggesting that the pathogen-induced mortality released adult perch from competition, thereby increasing somatic and reproductive growth. Higher juvenile survival after the pathogen outbreak due to a release from cannibalism likely contributed to the observed biomass overcompensation. Our findings have general implications for predicting population- and community-level responses to increased size-selective mortality caused by exploitation or disease outbreaks. 相似文献
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644.
Verina Ingram Julius Chupezi Tieguhong Jolien Schure Eric Nkamgnia Maurice Henri Tadjuidje 《Natural resources forum》2011,35(4):304-320
While mineral exploitation can provide significant income and employment, it may negatively impact the environment, being ultimately detrimental to livelihoods in the long term. The consequences of mining are of concern in high value forest ecosystems such as the Sangha Tri‐National (TNS) landscape covering Cameroon, the Central African Republic and Republic of the Congo. This paper captures the socio‐economic and environmental impacts of small‐scale mining in the TNS. Using structured questionnaires, consultations and observation, diamonds and gold were found to contribute directly to the livelihoods of at least 5% of the landscape's population. Although up to eight income‐generating strategies are used, mining contributes on average to 65% of total income and is used mainly to meet basic needs. A gold miner's average income is US$ 3.10 a day, and a diamond miner earns US$ 3.08, making them slightly wealthier than an average Cameroonian and three times wealthier than an average non‐miner in the TNS. Environmental impacts were temporary, low impact and of limited scale. However, with mining likely to increase in the near future, an increasing population and miners' low environmental awareness, measures are needed to ensure and reinforce the positive impact of artisanal mining on livelihoods and maintain its low environmental footprint in the TNS landscape. 相似文献
645.
Nicole E. Phillips 《Marine Biology》2011,158(10):2335-2342
This study evaluated whether larvae of the Indo-Pacific vermetid gastropod Dendropoma maximum are obligate planktotrophs, or whether they exhibit an intermediate feeding strategy. Experiments were conducted in Moorea,
French Polynesia (149°50′W, 17°30′S), Sep–Oct 2009, to examine D. maximum larval growth and metamorphic responses to different diets and amounts of food. Dendropoma maximum larvae required particulate food to undergo metamorphosis, but were able to survive and grow in the absence of food for up
to 20 days. Larvae in Low and Unfed food treatments exhibited phenotypic plasticity by growing a larger velum (the larval
feeding structure) compared with those in high food. Unfed D. maximum larvae had a slower initial growth rate; however, by 11-day post-hatch fed and unfed larvae had converged on the same mean
shell height (553 μm), which was only 10% larger than the initial size at hatching. Therefore, although the nutritional strategy
of D. maximum larvae is best described as obligate planktotrophy, it appears to approach an intermediate feeding strategy. 相似文献
646.
The aim of this study was to examine the effects of litter size and parity on sibling competition, piglet survival, and weight
gain. It was predicted that competition for teats would increase with increasing litter size, resulting in a higher mortality
due to maternal infanticide (i.e., crushing) and starvation, thus keeping the number of surviving piglets constant. We predicted
negative effects on weight gain with increasing litter size. Based on maternal investment theory, we also predicted that piglet
mortality would be higher for litters born late in a sow's life and thus that the number of surviving piglets would be higher
in early litters. As predicted, piglet mortality increased with increasing litter size both due to an increased proportion
of crushed piglets, where most of them failed in the teat competition, and due to starvation caused by increased sibling competition,
resulting in a constant number of survivors. Piglet weight at day 1 and growth until weaning also declined with increasing
litter size. Sows in parity four had higher piglet mortality due to starvation, but the number of surviving piglets was not
affected by parity. In conclusion, piglet mortality caused by maternal crushing of piglets, many of which had no teat success,
and starvation caused by sibling competition, increased with increasing litter size for most sow parities. The constant number
of surviving piglets at the time of weaning suggests that 10 to 11 piglets could be close to the upper limit that the domestic
sow is capable of taking care of. 相似文献
647.
Nearly all social spiders spin prey-capture webs, and many of the benefits proposed for sociality in spiders, such as cooperative
prey capture and reduced silk costs, appear to depend on a mutually shared web. The social huntsman spider, Delena cancerides (Sparassidae), forms colonies under bark with no capture web, yet these spiders remain in tightly associated, long-lasting
groups. To investigate how the absence of the web may or may not constrain social evolution in spiders, we observed D. cancerides colonies in the field and laboratory for possible cooperative defense and foraging benefits. We observed spiders’ responses
to three types of potential predators and to prey that were introduced into retreats. We recorded all natural prey capture
over 447 h both inside and outside the retreats of field colonies. The colony’s sole adult female was the primary defender
of the colony and captured most prey introduced into the retreat. She shared prey with younger juveniles about half the time
but never with older subadults. Spiders of all ages individually captured and consumed the vast majority of prey outside the
retreat. Young spiders benefited directly from maternal defense and prey sharing in the retreat. However, active cooperation
was rare, and older spiders gained no foraging benefit by remaining in their natal colony. D. cancerides does not share many of the benefits of group living described in other web-building social spiders. We discuss other reasons
why this species has evolved group living. 相似文献
648.
Altruism in the social Hymenoptera is generally considered to be a feature of females rather than males. A popular explanation
for this is that in the solitary ancestors of today's social species, males provided little brood care. Males might therefore
lack the preadaptations necessary to evolve altruism in social contexts. While anecdotal observations of male contributions
to colony life have been reported, there are few reports of male participation in nest defence. In apoid wasps, there have
been several reports of male nest-guarding behaviour in solitary species, potentially setting the evolutionary stage for similar
behaviours in social lineages. Here, we present evidence of active and effective nest defence in males of the social apoid
wasp Microstigmus nigrophthalmus. Males were observed chasing intruders away from the nest, and the presence of males had a significant effect on nest survival
when females were removed. Males potentially obtained direct benefits through defence, so that defence may not represent male
altruism. However, our results do show that males can perform acts that benefit their colony. 相似文献
649.
Peter Schippers Eric W.M. StienenAlex G.M. Schotman Robbert P.H. SnepPieter A. Slim 《Ecological modelling》2011,222(17):3061-3070
Most seabirds live in large colonies. This fact signifies that there is an advantage in living and breeding together. Four explanations are put fore ward for this colonial behaviour, more birds have: (1) a reduced per capita predation of chicks in colonies, (2) a better anti-predator defence, (3) a more efficient foraging in temporally patchy environments and (4) sex ratios that are more likely to be close to one. These factors induce a strong Allee-type density-dependent relation, a positive relation between density and population growth rate at low density. Nevertheless, these Allee effects are generally ignored in seabird population studies. Therefore we study the consequences of introducing Allee-type density-dependent relations in a spatially explicit metapopulation model for the Common Tern (Sterna hirundo). Simulations show that Allee effects might be responsible for a 20-fold decline in the recolonization distances, causing patches and parts of metapopulations to effectively become more isolated. This leads to long recolonization times of empty breeding patches which consequently cause slower metapopulation expansion and recovery. Additionally, we show that the typical early warning signals, that show that a population is near its critical threshold induce by Allee effects, is less pronounced in colonies that are part of a metapopulation. Hence, we offer some simple equations to estimate critical densities and thresholds in a colony. 相似文献
650.
Ruo-Qian Wang Adrian Wing-Keung Law E. Eric Adams Oliver B. Fringer 《Environmental Fluid Mechanics》2011,11(6):591-609
A series of Large Eddy Simulations (LES) are performed to investigate the penetration of starting buoyant jets. The LES code
is first validated by comparing simulation results with existing experimental data for both steady and starting pure jets
and lazy plumes. The centerline decay and the growth rate of the velocity and concentration fields for steady jets and plumes,
as well as the simulated transient penetration rate of a starting pure jet and a starting lazy plume, are found to compare
well with the experiments. After validation, the LES code is used to study the penetration of starting buoyant jets with three
different Reynolds numbers from 2000 to 3000, and with a wide range of buoyancy fluxes from pure jets to lazy plumes. The
penetration rate is found to increase with an increasing buoyancy flux. It is also observed that, in the initial Period of
Flow Development, the two penetrative mechanisms driven by the initial buoyancy and momentum fluxes are uncoupled; therefore
the total penetration rate can be resolved as the linear addition of these two effects. A fitting equation is proposed to
predict the penetration rate by combining the two independent mechanisms. 相似文献