Biological Control of Plant Invaders: Regional Patterns, Field Experiments, and Structured Population Models

Abstract

The traditional ways to design biological control systems for plant invaders include (in order of decreasing emphasis) introducing, augmenting, or conserving natural enemies. Manipulating consumer–resource relationships in this way (1) emphasizes top-down control of the invader by consumers rather than bottom-up control of the invader by limiting resources, and (2) contributes to a rising number of control organisms introduced to North America that is creating complexity, redundancy, and risk. New concepts and methods have started to transform the way biological control organisms are found and developed by (1) combining herbivore and resource limitation of plant population growth and (2) using targeted life-cycle disruption, which involves identifying plant life-cycle transitions that are both amenable to manipulation and influential on population growth, and then targeting these for control. To illustrate these developments, we outline an experimental and computational approach for measuring how the processes of disturbance, colonization, and organism interactions (plant competition and herbivory) manifest their influence on weed life cycles and population growth of ragwort Senecio jacobaea, a biennial or short-lived perennial herb. Manipulating these forces may lead to designs of biological control systems that are parsimonious, potent, and pose minimum risk to non-target organisms.