Mas-Carrió Eduard, Cornelissen Perry, Olff Han, Fumagalli Luca
Laboratory for Conservation Biology, Department of Ecology and Evolution, Biophore, University of Lausanne, Lausanne, Switzerland.
State Forestry Service, Amersfoort, The Netherlands.
Ecol Appl. 2025 Sep;35(6):e70090. doi: 10.1002/eap.70090.
In tropical grazer assemblies with abundant large predators, smaller herbivores have been shown to be limited by predation and food quality, while the larger species are regulated by food abundance. Much less is known about herbivore resource partitioning in temperate grazing ecosystems, where humans typically regulate large animal abundances. The Oostvaardersplassen ecosystem in the Netherlands is a unique multispecies assemblage of cattle, horses, red deer, and geese developed after the initial introduction of a few individuals in 1983. During the first 35 years, this herbivore assemblage without predation or human regulation gradually changed into an increasing dominance of the smaller herbivore species. Carrying capacity was reached around 2008, after which numbers started fluctuating depending on winter conditions. From 2018, management changed and population numbers became regulated for biodiversity and animal welfare reasons; however, population numbers still remained close to carrying capacity for several years. We used eDNA metabarcoding of dung to quantify the diet composition of cattle, horses, red deer, and geese, annually in early winter from 2018 to 2021 and calculated their niche overlap. We found strong interspecific diet overlap. Horse and cattle diets remained mostly stable with fluctuating densities of the different species, while only red deer diet showed density dependence. Interspecific niche overlap decreased with increasing red deer population size, the most abundant species. When calculated as total energy expenditure, we found that niche overlap was more linked to red deer abundance than to total herbivore energy intake. We suggest that red deer changed their diet mainly in response to their own population size, reducing their niche overlap in relation to their population increase. In this case, resource competition reduced resource availability and forced herbivores to consume different plant taxa. We conclude that in this predator-free temperate ecosystem, inter- and intraspecific resource competition are key factors structuring this assemblage of different size herbivores. We find a general competitive advantage of the more diet-flexible red deer over horses and cattle, but with also clear signs of resource partitioning.
在有大量大型食肉动物的热带食草动物群落中，较小的食草动物已被证明受到捕食和食物质量的限制，而较大的物种则受食物丰度的调节。对于温带放牧生态系统中食草动物的资源分配情况，人们了解得要少得多，在温带放牧生态系统中，人类通常会调节大型动物的数量。荷兰的奥斯特瓦尔德斯普拉森生态系统是一个独特的多物种组合，包括牛、马、马鹿和鹅，这是在1983年最初引入少数个体后发展起来的。在最初的35年里，这个没有捕食或人类调节的食草动物群落逐渐转变为较小食草动物物种的优势度不断增加。大约在2008年达到了承载能力，此后数量开始根据冬季条件波动。从2018年起，管理方式发生了变化，出于生物多样性和动物福利的原因，种群数量得到了调控；然而，种群数量在几年内仍接近承载能力。我们利用粪便的环境DNA宏条形码技术，在2018年至2021年每年初冬对牛、马、马鹿和鹅的饮食组成进行量化，并计算它们的生态位重叠。我们发现种间饮食重叠很强。马和牛的饮食大多保持稳定，不同物种的密度有所波动，而只有马鹿的饮食表现出密度依赖性。种间生态位重叠随着最丰富的物种——马鹿种群规模的增加而减少。当以总能量消耗来计算时，我们发现生态位重叠与马鹿的丰度比与食草动物的总能量摄入量的联系更为紧密。我们认为，马鹿主要根据自身种群规模改变其饮食，随着种群增加，减少了它们的生态位重叠。在这种情况下，资源竞争降低了资源可用性，并迫使食草动物食用不同的植物类群。我们得出结论，在这个没有捕食者的温带生态系统中，种间和种内资源竞争是构建这个不同体型食草动物组合的关键因素。我们发现饮食更具灵活性的马鹿相对于马和牛具有普遍竞争优势，但也有明显的资源分配迹象。
