The composition of an ecosystem is thought to be important for determining its resistance to invasion. Studies of natural ecosystems, from plant to microbial communities, have found that more diverse communities are more resistant to invasion. In some cases, more diverse communities resist invasion by more completely consuming the resources necessary for the invader. We show that Escherichia coli can successfully invade cultures of the alga Chlamydomonas reinhardtii (phototroph) or the ciliate Tetrahymena thermophila (predator) but cannot invade a community where both are present. The invasion resistance of the algae-ciliate community arises from a higher-order interaction between species (interaction modification) that is unrelated to resource consumption. We show that the mode of this interaction is the algal inhibition of bacterial aggregation, which leaves bacteria vulnerable to predation. This mode requires both the algae and the ciliate to be present and provides an example of invasion resistance through an interaction modification.

人们认为，生态系统的组成对于确定其对入侵的抵抗力很重要。从植物群落到微生物群落的自然生态系统研究都发现，越多样化的群落对入侵的抵抗力就越大。在某些情况下，更多样化的社区通过更完全地消耗入侵者所需的资源来抵制入侵。我们表明，大肠杆菌 可以成功地入侵藻类莱茵衣藻（光养）或纤毛四膜虫嗜热的文化。（捕食者），但无法入侵同时存在两者的社区。藻类纤毛虫群落的入侵抵抗力是由于物种之间的高级相互作用（相互作用修饰）引起的，而这种相互作用与资源消耗无关。我们表明这种相互作用的模式是藻类抑制细菌聚集，使细菌容易被捕食。该模式需要藻类和纤毛虫同时存在，并通过相互作用修饰提供了抗入侵性的实例。