When there is conspicuous underexploitation of a limited resource, it is worth asking, what mechanisms allow presumably valuable resources to be left unused? Evolutionary biologists have generated a wide variety of hypotheses to explain this, ranging from interdemic group selection to selfishly prudent individual restraint. We consider a situation in which, despite high intraspecific competition, individuals leave most of a key resource unexploited. The parasitic wasp that does this finds virtually all host egg clusters in a landscape but parasitizes only about a third of the eggs in each and then leaves a deterrent mark around the cluster. We first test-and reject-a series of system-specific simple constraints that might limit full host exploitation, such as asynchronous maturation of host eggs. We then consider classical hypotheses for the evolution of restraint. Prudent predation and bet-hedging fail as explanations because the wasp lives as a large, well-mixed population. Additionally, we find no individual benefits to the parasitoid of developing in a sparsely parasitized host nest. However, an optimal foraging model, including empirically measured costs of superparasitism and hyperparasitism, can explain through individual selection both the consistently low rate of parasitism and deterrent marking.
The rapid increase in atmospheric CO2 concentrations (Ca ) has resulted in extensive research efforts to understand its impact on terrestrial ecosystems, especially carbon balance. Despite these efforts, there are relatively few data comparing net ecosystem exchange of CO2 between the atmosphere and the biosphere (NEE), under both ambient and elevated Ca . Here we report data on annual sums of CO2 (NEE(net) ) for 19 years on a Chesapeake Bay tidal wetland for Scirpus olneyi (C3 photosynthetic pathway)- and Spartina patens (C4 photosynthetic pathway)-dominated high marsh communities exposed to ambient and elevated Ca (ambient + 340 ppm). Our objectives were to (i) quantify effects of elevated Ca on seasonally integrated CO2 assimilation (NEE(net) = NEE(day) + NEE(night) , kg C m(-2) y(-1) ) for the two communities; and (ii) quantify effects of altered canopy N content on ecosystem photosynthesis and respiration. Across all years, NEE(net) averaged 1.9 kg m(-2) y(-1) in ambient Ca and 2.5 kg m(-2) y(-1) in elevated Ca , for the C3 -dominated community. Similarly, elevated Ca significantly (P < 0.01) increased carbon uptake in the C4 -dominated community, as NEE(net) averaged 1.5 kg m(-2) y(-1) in ambient Ca and 1.7 kg m(-2) y(-1) in elevated Ca . This resulted in an average CO2 stimulation of 32% and 13% of seasonally integrated NEE(net) for the C3 - and C4 -dominated communities, respectively. Increased NEE(day) was correlated with increased efficiencies of light and nitrogen use for net carbon assimilation under elevated Ca , while decreased NEE(night) was associated with lower canopy nitrogen content. These results suggest that rising Ca may increase carbon assimilation in both C3 - and C4 -dominated wetland communities. The challenge remains to identify the fate of the assimilated carbon.
The resilience of Caribbean coral reefs, which are an important source of biodiversity and provide essential ecosystem services, is constantly challenged by many reef stressors including ocean acidification, hurricane damage, and overharvesting of herbivorous reef fish. The presence of two alternative stable states-a desirable state with high levels of coral cover and its coral-depleted counterpart-has been widely documented in the literature. Increasing coral resilience to prevent phase shifts to the undesirable state is a critical research priority, and mathematical models can serve as an important tool to not only better understand the underlying dynamics of observed coral communities, but also to evaluate the potential impacts of stressors and the outcome of management strategies designed to promote coral persistence. Here, we review the existing literature of mathematical models designed to understand the processes that generate alternative stable states. We focus on models that are comprised of ordinary differential equations and, at their core, capture algal-coral dynamics. Recommendations for Resource Managers• Evidence for the existence of alternative stable states and the associated presence of hysteresis implies a need for management designed to increase the resilience of coral reef ecosystems.• In addition, holistic approaches to designing management strategies are required to both increase resilience of Natural Resource Modeling. 2018;31:e12157.wileyonlinelibrary.com/journal/nrm
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