Novel weapons: invasive success and the evolution of increased competitive ability

Abstract

When introduced to new habitats by humans, some plant species become much more dominant. This is primarily attributed to escape from specialist consumers. Release from these specialist enemies is also thought by some to lead to the evolution of increased competitive ability, driven by a decrease in the plant's resource allocation to consumer defense and an increase in allocation to size or fecundity. Here, we discuss a new theory for invasive success – the “novel weapons hypothesis”. We propose that some invaders transform because they possess novel biochemical weapons that function as unusually powerful allelopathic agents, or as mediators of new plant–soil microbial interactions. Root exudates that are relatively ineffective against their natural neighbors because of adaptation, may be highly inhibitory to newly encountered plants in invaded communities. In other words, the novel weapons of some plant invaders provide them with an advantage that may arise from differences in the regional coevolutionary trajectories of plant communities. Furthermore, the selective advantage of possessing a novel weapon may result in rapid evolution of that weapon – for example, the production of greater quantities of allelopathic or antimicrobial root exudates. Direct selection of competitive traits provides an alternative to the “grow versus defend” trade‐offs that underpin the theory of the evolution of increased competitive ability.

Framing Sustainability in a Telecoupled World

“…For instance, relationships between governments and corporations are important to drive bilateral trade flows between Brazil and China in the soybean trade example (Niu 2010 For establishing new telecouplings, innovative agents that are flexible in their requirements may be most often successful, but different characteristics, such as resilience, may matter more for maintaining and strengthening an existing telecoupling. Alien species like the RIFA take hold and become invasive in receiving systems when they thrive in new biotic conditions and outcompete natives for limited resources (Callaway and Ridenour 2004). The soybean trade between Brazil and China has thrived in part because the flexible trade agreements adopted by Brazil and China allow the systems to adapt to new markets and opportunities, and because there are highly effective commodity value chains linking producing regions with the main markets abroad.…”

Conceptual Frameworks and Methods for Advancing Invasion Ecology

“…For example, the enemy release hypothesis is connected to the novel weapons hypothesis. The latter hypothesis suggests that invasive species can have a competitive advantage over native species because they possess a trait that the native species are not evolutionarily adapted to and therefore affects them negatively (Callaway and Ridenour 2004). A shared idea is that missing eco-evolutionary 'experience' of the resident species with the invader can be advantageous for alien species.…”

A non‐native invasive grass increases soil carbon flux in a Hawaiian tropical dry forest

“…Non-native invasive species most likely to alter ecosystem processes are those that: (i) differ from natives in resource acquisition and utilization, (ii) alter trophic structures, or (iii) influence disturbance regimes (Vitousek, 1990). The success of invasive plants has been at least partially linked to all three of these mechanisms (Mack et al, 2000;Daehler, 2003;Callaway & Ridenour, 2004).…”