A proposal to use plant demographic data to assess potential weed biological control agents impacts on non-target plant populations

Bernd Blossey,Wade Simmons,Jianqing Ding,Andrea Dávalos

doi:10.1007/s10526-018-9886-4

Abstract

Weed biocontrol programs aim to reduce the spread and population growth rate of the target plant while stabilizing or increasing populations of those native species considered under threat by invasive plants. This goal is not unique to weed biocontrol but applies to all other invasive plant management techniques, though such information is rarely collected. Without this information, success of management interventions can be ambiguous, and regulatory agencies, the public, policy makers, funders and land managers cannot be held accountable for chosen treatments. A fundamental reform, including use of demographic studies and long-term assessments, are essential to guide weed biocontrol programs. We propose to add use of plant demography (an assessment of how environmental factors and ecological interactions, for example competition, disease or herbivory, may affect plant populations by altering survival, growth, development and reproductive rates of plant individuals) during host specificity risk assessments of potential biological control agents. Demographic models can refine assessments of potential impacts for those plant species that experience some feeding or larval development during host specificity testing. Our proposed approach to focus on impact on plant demography instead of attack on plant individuals is useful in appropriately gauging threats potential weed biocontrol agents may pose to non-target species after field release.

Highlights

Biological weed control programs aim to find organisms able to reduce spread and population growth rate of target plants, while avoiding non-target impacts
At a time when it is becoming increasingly evident that many invasive species control methods, chemical management, are unable to achieve lasting control and may threaten non-target species (Kettenring and Adams 2011; Pearson et al 2016), we argue that it is time for fundamental reform of risk assessment and decision making processes in invasive plant management and weed biocontrol that is guided by appropriate scientific information and open dialogue, not fear (Blossey 2016b)
After ten years simulated populations increased from 1000 plants to [ 40,000 plants when attacked by G. nymphaeae, but declined to near zero individuals under G. birmanica attack (Fig. 3)

Summary

Introduction

Biological weed control programs aim to find organisms able to reduce spread and population growth rate of target plants, while avoiding non-target impacts. Similar demographic experiments with rare plants that are part of the fundamental host range of M. crucifer could help evaluate real (vs feared) threats to other US native Boraginaceae These examples showcase the value of detailed demographic studies to assess how attack by biocontrol agents may, or may not, contribute to harm, or endangerment of non-target species. Gmelin (Cabombaceae), the only other plant reported to be attacked in the field (Ding et al 2006a) (natural histories of T. natans, B. schreberi, G. nymphaeae and G. birmanica are provided in Supplementary Materials, Section 1) Both herbivores were evaluated as potential biocontrol agents in experiments that assessed their impact on growth and reproduction of T. natans at different larval densities (0–50 L1 per rosette) (Ding and Blossey 2005; Ding et al 2006b). We conducted all analysis using package popbio (Stubben and Milligan 2007) in R Core Team (2016)

Results of demographic analyses

Results from modelled simulations

Discussion