|The passage suggests that Lack would agree with which of the following statements about factors affecting clutch size in birds?|
|An alarming number of Mediterranean monk seals, an endangered species, have recently died. Postmortem analysis showed the presence of an as yet unidentified virus, as well as evidence of a known bacterial toxin. Seawater samples from the area where the seals died did contain unusually high concentrations of the toxic bacterium. Therefore, although both viruses and bacterial toxins can kill seals, it is more likely that these deaths were the result of the bacterial toxin.|
|Which of the following, if true, provides additional evidence to support the conclusion?|
|Which of the following, if true, provides the strongest support for the argument given?|
Although many hypotheses have been proposed to explain why some plant communities are more susceptible than others to invasion by nonnative species, results from field studies have been inconsistent and no general theory of invasibility has yet emerged. However, a theory based on fluctuating resource availability could integrate most existing hypotheses and successfully resolve many of the apparently conflicting and ambiguous results of previous studies. The suggested theory is that a plant community becomes more susceptible to invasion whenever there is an increase in the amount of unused resources.
The diversity in the range of resource-release mechanisms could partly explain the absence of consistent ecological correlates of invasibility. In particular, the theory predicts that there will be no necessary relationship between the species diversity of a plant community and its susceptibility to invasion, since near-complete exploitation can each occur in both species-rich and species-poor communities. Though Lonsdale found a positive association between species richness and invasion, this may arise from the tendency of diverse plant communities to be nutrient poor and therefore more responsive to the effects of human-caused influxes of nutrients.