Insect Seed Predators as Important as Pollinators

Recent research published in the British Ecological Society’s Journal of Applied Ecology suggests greater attention ought to be paid to seed predators, especially in the context of natural and agro-ecosystems.

Whilst a great deal of work and policy has focused on the functional importance of pollinators in the agricultural landscape, scant attention has duly been paid to insect seed predators.

A body of work has shown that the experimental removal of insect seed predators can have positive effects on annual plant populations. Insect predators play an important role in competition, specifically apparent competition. Apparent competition is where for example, two tree species appear to compete for similar resources, yet are in fact limited by a shared natural enemy that in turn responds to changes in abundance or distribution of either species.

Although apparent competition is thought to be widespread, so far few studies have so far been able to quantify this effect in long-lived species. Food webs, that describe the abundance and interaction of different species within a community can reveal the importance of this effect. Research in Sarawak tropical forests has shown that the diet of insect predators depends heavily on the abundance of their favoured prey type.

Humans can also directly and indirectly mediate the impact of insect seed predation. Given how sensitive insects are to light and humidity, even if a logged area of rainforest retains an insect’s main food source, the change in local conditions could have seriously detrimental affects on the insect population. The resulting change in abundance and distribution of insect species could thus have serious consequences for local plant community dynamics.

Many scientists consider tropical forests to be more resilient to climate change than other ecosystems. Changes in the phenology of plants (timing of flowering), could result in asynchrony with insect predators. If plant species begin to bare fruit more regularly this could result in elevated insect predator populations. It is thought that increased predator numbers could thus reduce the rate of forest regeneration.

Thought should be given to the impacts of plant or seed predators introduced to combat invasive species, especially in the context of changes that could occur in the wider food web. The authors recommend that insect predators should be given equivalent consideration to functionally important groups such as pollinators, in the wider research agenda.

Source: Lewis, O.T. & Gripenberg, S. (2008) Insect seed predators and environmental change, Journal of Applied Ecology, DOI: 10.1111/j.1365-2664.2008.01575.