Kulkarni Devdutt, De Laender Frederik
Laboratory of Environmental Ecosystem Ecology, Research Unit in Environmental and Evolutionary Biology (URBE), University of Namur, Namur, Belgium.
PLoS One. 2017 Mar 1;12(3):e0172828. doi: 10.1371/journal.pone.0172828. eCollection 2017.
Food web structure and species richness are both subject to biotic (e.g. predation pressure and resource limitation) and abiotic stress (e.g. environmental change). We investigated the combined effects of both types of stress on richness and connectance, and on their relationship, in a predator-prey system. To this end, we developed a mathematical two trophic level food-web model to investigate the effects of biotic and abiotic stress on food web connectance and species richness. We found negative effects of top-down and bottom-up control on prey and predator richness, respectively. Effects of top-down and bottom-up control were stronger when initial connectance was high and low, respectively. Bottom-up control could either aggravate or buffer negative effects of top-down control. Abiotic stress affecting predator richness had positive indirect effects on prey richness, but only when initial connectance was low. However, no indirect effects on predator richness were observed following direct effects on prey richness. Top-down and bottom-up control selected for weakly connected prey and highly connected predators, thereby decreasing and increasing connectance, respectively. Our simulations suggest a broad range of negative and positive richness-connectance relationships, thereby revisiting the often found negative relationship between richness and connectance in food webs. Our results suggest that (1) initial food-web connectance strongly influences the effects of biotic stress on richness and the occurrence of indirect effects on richness; and (2) the shape of the richness-connectance relationship depends on the type of biotic stress.
食物网结构和物种丰富度都受到生物因素（如捕食压力和资源限制）和非生物胁迫（如环境变化）的影响。我们研究了这两种胁迫对一个捕食者 - 猎物系统中丰富度、连通性及其关系的综合影响。为此，我们开发了一个数学两营养级食物网模型，以研究生物和非生物胁迫对食物网连通性和物种丰富度的影响。我们发现自上而下和自下而上的控制分别对猎物和捕食者的丰富度有负面影响。自上而下和自下而上控制的影响分别在初始连通性高和低时更强。自下而上的控制可能会加剧或缓冲自上而下控制的负面影响。影响捕食者丰富度的非生物胁迫对猎物丰富度有正向间接影响，但仅在初始连通性低时才出现。然而，在对猎物丰富度有直接影响之后，未观察到对捕食者丰富度的间接影响。自上而下和自下而上的控制分别选择了弱连接猎物和强连接捕食者，从而分别降低和增加了连通性。我们的模拟表明存在广泛的丰富度 - 连通性负向和正向关系，从而重新审视了食物网中丰富度与连通性之间常见的负向关系。我们的结果表明：（1）初始食物网连通性强烈影响生物胁迫对丰富度的影响以及对丰富度间接影响的发生；（2）丰富度 - 连通性关系的形状取决于生物胁迫的类型。
