Reintroduction of large predators may affect ecosystem functions

Writing / Irene Vega

Trophic cascades are mechanisms that structure ecosystems from their upper levels (predators) to their lower levels (plants) through food chains. In this sense, superpredators, which are at the top of food chains, can cause the so-called effects top-down, altering the abundance and behavior of species found at lower trophic levels. This is the case of medium-sized mammals (sables and foxes), which play an important role as seed dispersers of many plants with fleshy fruits.

A new study, led by researchers from the Rey Juan Carlos University and published in the scientific journal Functional Ecology, reveals a novel trophic cascade from the Iberian lynx - the largest regional predator in southern Spain - to the community of plants with fleshy fruits dispersed by carnivorous and frugivorous mammals (since they also feed on fruits) in this Mediterranean ecosystem.

The research has compared the quantity and quality of the seed dispersal service that these mammals provide to plants between areas with lynxes and without lynxes in the Sierra de Andújar Natural Park (southern Spain). The researchers carried out the study by combining traditional and novel analytical techniques, such as diet analyzes to quantify seed dispersal and DNA analyzes (genetic barcoding) to identify the mammal species that dispersed the seeds.

“Although the study area lacks reintroduced lynx populations, the heterogeneous distribution of the Iberian lynx throughout the Natural Park and the rich community of fleshy fruit and carnivorous plants that inhabit the area represented a unique opportunity to carry out this experimental field study. ", highlights Tamara Burgos, the main author of the article and researcher in the Biodiversity and Conservation Area of ​​the URJC.

The lynx reduces the quantity and diversity of seed dispersal

The study shows that the quantity and diversity of seeds dispersed by medium-sized carnivores decreased drastically in the presence of lynxes. The researchers found that this effect was strongest for the marten, finding a marked reduction in the number of droppings containing seeds (93% less) and the diversity of seeds it dispersed (46% less) within the lynx's territories.

According to Emilio Virgós, one of the main researchers of this study: “large predators usually control the abundance and behavior of smaller predators through direct predation or other types of competitive interactions. Lynxes can easily kill foxes and martens or simply scare them away with their mere presence. “We observed that the combined effect of these two processes significantly reduced seed dispersal.”

Foxes dispersed fewer seeds in open environments within the lynx's range 

The red fox was the most abundant carnivorous species and the one that dispersed the most seeds. However, foxes dispersed 68% fewer seeds in open habitats when they coexisted with lynxes. This behavioral alteration is probably related to the instinct to avoid high-risk habitats, but could contribute to modifying the dynamics of forest regeneration and landscape structure in the long term.

However, as Tamara Burgos points out: “other frugivores not affected by the presence of lynxes, such as birds or larger mammals, could compensate for the reduction in seed dispersal services by foxes and martens within the areas of reintroduction of lynxes. However, the study region is a typical defaunated scenario in central and southern Europe, where large fruit-eating mammals such as the brown bear are extinct. Birds are the primary seed dispersers of many plants, but physical limitations based on beak width can limit seed dispersal of large-fruited plants. In this sense, mammals play a key role.”

Implications of trophic cascades in plant ecology

To date, restoring apex predators has been proven to be a successful conservation tool to save them from extinction. However, this study shows that attention should be paid to the possible impacts of trophic cascades before planning reintroduction programs for large predators. Furthermore, as this research reveals, it is especially important to take it into account in altered and defaunated ecosystems, where specialist frugivorous species are lacking and carnivores provide unique services to plants.

"Although we have evaluated trophic cascades at a local scale, we consider that our study may have broad application and we encourage reintroduction programs to consider cascading impacts as powerful effects that can alter key ecosystem functions in countless ways," concludes Tamara. Burgos.