Date of this Version
TRENDS in Biotechnology 2007; Vol.25 No.12
The concept of ecological ‘traps’ is based in theory from ecology and conservation biology that has now found application to infectious diseases with a study from Paul Turner’s group. This study is important because it offers a mathematical model of ecological traps, applies this model to viruses, and tests the model in a bacteria– phage system. Although there will be technical hurdles to overcome, this concept might lead to benefits for both health and industry.
An ecological trap is defined as a habitat that is suboptimal for growth or for reproduction of a population, but that is preferred to the optimal habitat by members of the population , typically in response to a specific environmental cue . The concept has primarily been a topic of concern in conservation biology, invoked when species of interest choose an anthropogenically altered habitat over a more pristine counterpart, resulting in a negative effect on the population . The concept of the ecological trap derives from source-sink theory. This theory postulates that there are certain habitats for any given species that provide superior conditions for population growth, and which are therefore a source for individuals and genes moving to other habitat-types. The theory further postulates that other habitat-types support low or no reproduction, and are ‘sinks’ for individuals or genes from the source habitats; these populations are only maintained by continued emigration from the sources. A trap differs from a sink in that a trap habitat is actively preferred over the most suitable habitat, or source. Therefore, individuals are attracted to this unsuitable habitat, and the population might become trapped there, unable to maintain reproduction at a high enough level to sustain the population.
Organisms are thought to follow specific environmental cues that identify high-quality habitats and lead to optimization of organism fitness. Over time, populations presumably evolve to recognize cues from what are, by definition, the most favorable habitats. However, ecological traps occur when sub-optimal habitats present the same cues as the optimal habitat, luring the organism away from the optimal habitat, and resulting in a decline in organism fitness. What was once a specific adaptation for choosing the best habitat therefore becomes maladaptive. One frequently cited example is that of sea turtle hatchlings following artificial lights. Light cues on the horizon signaled the direction of the ocean, until recently when humans introduced artificial lighting from beachfront properties – in the opposite direction of the ocean . Traps such as this are suspected to exist in many contexts in which the environment has changed quickly, and the ability of the organism to discriminate between habitats has not had time to compensate .
In contrast to the central goal of conservation biology, which seeks to preserve rare species, ecological traps can be used to manipulate an undesirable species toward extinction. This approach has been investigated in agricultural systems, in which various species of plants can be used to attract insect pests away from commercial crops . The concept of the trap might also be used in medicine, for example to trap agents of disease in, or on, the human body. The trap habitat concept seems particularly appropriate for the fight against viral disease. For instance, a cell might attract and bind viruses by expressing appropriate receptors on its surface, but then fail to support viral replication, and thereby trap virions either inside the cell or on the cell exterior, leading to their clearance from the body.