Bridging ecology and conservation: from ecological networks to ecosystem function, Harvey et al. 2017

This article emphasizes the importance of species interactions as drivers of ecosystem function.

The classic conservation approach is to set aside national parks or to target specific species for protection, based on their rarity or endangered status. However, these approaches can have trade-offs for non-target species, while also potentially failing to protect ecosystem function. The authors, therefore, suggest that species interactions based on their functional significance should be the main focus on conservation efforts.

We propose that a shift in focus from species to interaction networks is necessary to achieve pressing conservation management and restoration ecology goals of conserving biodiversity, ecosystem processes and ultimately landscape-scale delivery of ecosystem services [Harvey 2017: 371].

Species depend on many other species in their communities, either directly or indirectly. An example of indirect dependence is the Phengaris arion butterfly’s need for European rabbits. The butterfly uses ant nests made in the open areas supplied by rabbit grazing for development of its larvae. Thus, no rabbits means no ants, which means no Phengaris arion.

Focusing on species interactions is more meaningful even than measuring species richness (the number of different species), because interactions can disappear – even if both species are present – if either group’s abundance has significantly dropped. The authors offer the example of 59 regionally extinct lepidoptera (butterfly and moth) species of central Europe. Eight of these extinctions were associated with the loss of particular host plant species, which actually occurred after the lepidoptera went extinct.

Thus, strong declines of host plants can have cascading extinction effects on higher trophic levels before the plants actually go extinct, illustrating that interactions can be lost before any actual decline in species richness (plants persisted at low abundance). This illustrates that preserving keystone interactions, rather than species, can be a proactive way to maintain ecosystem integrity in the face of global change instead of allocating resources to already endangered species [Harvey 2017: 372].

There is interdependence among species even between neighboring ecosystems. For example, a manta ray species in the Palmyra Atoll south of Hawaii depends on two species of native trees to maintain its ocean plankton diet. When these trees were replaced with cultivated coconut palms, marine-foraging birds no longer nested on that shore, depriving the coastal waters of the nitrogen runoff from their guano, which had been feeding the plankton population.

The authors recommend that “the main lever to restore or conserve ecological network structure and stability is the management of spatial configuration” [Harvey 2017: 377]. Reflecting on the Palmyra Atoll, for example, it’s clear that a marine conservation plan would be incomplete without considering the nutrient flow from the tree-bird interactions on land.