Ecosystem services provided by bats

Biological control was originally defined as “the action of parasites, predators, or pathogens in maintaining another organism’s population density at a lower average than would occur in their absence.” By this definition, biological control differentiates itself from other pest management techniques in that it operates in a density-dependant manner, i.e. natural enemies will increase in intensity to control a similarly increasing population of pests. In an ecological sense, biological control can be seen as a strategy to restore biodiversity in agro-ecosystems by adding ‘missing’ entomophagous (insect-eating) insects or by enhancing naturally occurring predators through habitat management.

South Africa is classified among the three world leaders in biological control of invasive plants, and more than 80 biological control agents have been released to control 35 problem plant species (Agricultural Research Council; The principles of Biological Control of Weeds). Caution should however be taken when importing foreign control agents. The Cane Toads in Australia which originally introduced to control the native Cane Beetle which causes huge damage to sugar cane plantations, are a perfect example of biological controls gone wrong. Originally introduced from Hawaii in 1935, the 102 originators bred with huge success and now number some 200 million and are known to spread diseases affecting local biodiversity ( "Institute for Molecular Bioscience, Killing off the cane toad").

With this in mind, a local approach should always be considered first and should be the driving force behind many burgeoning bio-control projects. One such project that EcoSolutions has recently undertaken is an investigation into the degree to which bats can exert population control on certain pest insect species, such as the False codling moth.

Bats belong to the order of mammals called Chiroptera, meaning ‘hand-wing’. There are more than 1 100 recognised species of bats on the world, almost one fifth of the total 5416 mammalian species listed by Wilson and Reader (2005). Bats occur worldwide, except in extreme polar and desert habitats and Southern Africa is home to 75 species.

Traditionally bats have been characterised into two sub-orders, Megachiroptera and Microchiroptera, although researchers have proposed alternate views of chiropteran phylogeny and classification. For the sake of simplicity, we will stick to the traditional method. Megachiroptera or fruit-eating bats are responsible for pollinating huge tracts of land whilst Microchiroptera or insect-eating bats are known as natures pesticides. Insectivorous bats are by far the larger group and should be welcome guests in any ecosystem. A colony of 300 000 bats in the De Hoop Nature Reserve consumes an estimated 100 tonnes of insects per year whilst a study in the USA estimated that a colony of 150 Big Brown Bats can eat up to 1.3 million insects a year (Whitaker, J.O., Am. Midl. Nat. 134, 346).

Using bats as a control measure in agriculture is no new science. Certain parts of the Southern USA and in particular, areas in Texas are home to colonies of over 1 million bats. Studies have been conducted in several of these areas to calculate the eco-agricultural contribution by bats, and a conservative estimate has put this figure at US$3.7 billion dollars, whilst other estimates have predicted a potential impact in excess of US$50 billion. These figures take into account a number of different factors including the reduced costs of pesticide applications that are not needed to suppress pests consumed by bats but do not include ‘downstream’ factors of reduced pesticide exposure to ecosystems which could be substantial (Boyles, JG. et al, Economic Importance of Bats in Agriculture, Science 332(6025): 41-42).

Our current work has the primary objective of establishing the agro-economic benefits provided by bats. Through habitat enhancement and the provision of roosting sites, it is possible to encourage greater habitation of bats in and around areas where their ‘pest control services’ are most needed. As a result of our ongoing investigations and regular monitoring of sites, we aim to establish traits that are most beneficial in encouraging bat habitation. The information collected from these investigations will go a long way to providing robust data in support of the contributions bats can have in agriculture which will further add to the conservation of these animals.

The initial phase of the project began in October 2010 with bat houses being installed across 10 farms in the Western and Eastern Cape.

If you are interested in the project or know of someone who is already undertaking something of a similar nature please let us know.

A view looking up at a range of our bat boxes installed on a farm in the Eastern Cape