病原体感染对物种间资源竞争的影响——基于资源竞争理论

病原体感染对种间竞争的影响可能是因为改变了宿主的资源利用过程，然而竞争模型（Lotka-Volterra）由于参数化竞争系数而忽略了资源的动态变化过程，因此基于此类模型的研究无法揭示病原体对宿主资源利用的影响。基于Tilman的资源竞争理论构建了病原体感染一个物种的资源竞争模型，通过分析宿主物种资源利用效率的变化探讨了病原体对种间竞争的影响。结果表明：（1）病原体降低了宿主对资源的消耗率（消费矢量变短），抬高了对资源的最低需求（零等倾线上移），这意味着宿主的竞争力减弱；（2）虽然感染影响了竞争物种的密度，但不会改变共存物种的共存状态；（3）病原体可以使宿主物种的竞争对手更容易入侵，形成共存局面，极大地扩大了竞争物种共存的参数范围，本质上促进了物种多样性维持；（4）病原体的传播率和毒性也复杂地影响了竞争物种共存，传播率越大越能促进物种共存，而中等强度毒性最能促进物种共存。研究结果明确了病原体对物种资源利用模式的潜在改变，强调了病原体在物种共存和生物多样性维持中的重要性。

Effect of pathogen infection on resource competition between species: a study based on resource competition theory

There is growing evidence that pathogens can affect the outcomes of interspecific competition, which may arise indirectly because infection alters the resource utilization of the host. The direct effects of infection on host fitness (generally negative) and the consequences of indirect effects on other species (positive or negative) mediated by host species ultimately dictate species coexistence. Pathogens can adjust interspecific competition by affecting consumer-resource interactions. These indirect effects may transmit through food webs and ripple throughout the ecological communities, and thus possibly affect ecosystem functioning and resilience. Therefore, it is necessary to consider the role of indirect effects of pathogens in species coexistence and community construction. The existing theoretical studies of pathogen-mediated competition, however, are based on phenomenological models (e.g., the Lotka-Volterra competition model). As these models do not specify the mechanism of competition between species, they neither specify what the species compete for nor how they compete. These models use some parameters (e.g., the competition coefficient) to describe the effects of one species on the per capita growth rates of the other species in a community, ignoring the interaction between consumers and resources, and resource dynamics. Thus, using such phenomenological models, it is impossible to capture how pathogens mediate exploitative competition by influencing the resource utilization of their host. To better understand this process, based on resource competition theory (explicitly incorporating resource consumption), we constructed a specialist pathogen-mediated resource competition model in which two species compete for two abiotic essential resources, and one of the competitors can be infected by a directly transmitted specialist pathogen. Our motivation is to understand how the combination of two different interspecific interactions (parasitism and interspecific resource competition) determines species coexistence and community structure. Then, we conducted the analysis and computer simulations of the model. The results showed that:(1) pathogens reduced the host''s consumption rate of resources (shorter consumption vector) and raised the host''s resource requirement (upward shift of the zero isoclines), which implied a weakening of the host''s competitiveness. (2) Although specialist pathogen infection affects the density of the host, it does not change the coexistence status of co-existing species. (3) Specialist pathogens can make it easier for the non-host competitor to invade, resulting in a coexistence situation, which greatly increases the likelihood of the coexistence of competing species and essentially contributes to the maintenance of species diversity. (4) The transmission rate and virulence of specialist pathogens have complicated effects on the coexistence of competing species, with high transmission and moderate virulence promoting species coexistence the most. Our results clarify pathogens'' potential alteration of species resource utilization patterns and highlight the importance of pathogens in species coexistence, biological invasions, and maintenance of species diversity.