生物学上的假设包括生态变化，这些变化是由昆虫和开花植物之间的共同进化，或海洋中以海底生物为食的捕食者的进化所带来的。
Biological hypotheses include ecological changes brought about by the evolution of cooperation between insects and flowering plants or of bottom-feeding predators in the oceans.
有证据表明，这一时期发生了重大的生态和地质变化。
There is evidence of major ecological and geological changes during this period.
由于其中可能涉及复杂的物种相互作用，通过移除一个关键物种并观察生态系统的变化来确定该物种是有问题的。
Because complex species interactions may be involved, identifying a keystone species by removing the species and observing changes in the ecosystem is problematic.
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