Predicting potential recovery of the endangered bromeliad Tillandsia utriculata: An agent-based modeling approach

TL;DR

This study uses computer models to explore how an invasive weevil affects the endangered Florida bromeliad and its chances of recovery.

Contribution

The paper introduces an agent-based model to simulate evolutionary and ecological responses of Tillandsia utriculata to weevil predation.

Findings

Weevil predation requires higher germination rates for population viability over 100 years.

The minimum rosette size for reproduction decreased over time, even without weevils.

Earlier reproduction due to weevil pressure may threaten long-term survival.

Abstract

Invasive pests and pathogens are a major driver of biodiversity loss. Some rare species may persist through rapid evolution to tolerate or escape new threats, but representing the underlying ecological and evolutionary processes at the appropriate scale is analytically and computationally challenging. Tillandsia utriculata has been classified as endangered in Florida where its population has decreased significantly due to predation by the invasive Mexican weevil Metamasius callizona. Adult female weevils deposit their eggs in leaves of epiphytic bromeliads, preferentially ovipositing in the largest rosettes. Once the eggs hatch, the larvae consume the core of the rosette, often leading to pre-reproductive death. During the past three decades of predation, the T. utriculata population has shifted to initiating the production of inflorescences (to commence its single attempt at sexual reproduction) at smaller rosette sizes. Importantly, the rosette size at induction is correlated with the number of seeds produced. We have constructed an agent-based model to simulate the dynamics of a Florida T. utriculata population over many generations where the minimum rosettes size required to initiate inflorescence production (minimum size of induction or MSI), is an inherited trait. We use the model to explore how predation may have shifted the population’s genetic composition and the impact this has on population viability. Our results show that larger germination rates are required for population viability when weevils are present. Parameter uncertainty analysis revealed that in the presence of weevil predation, only a population with a very high germination rate and a short period of predation would sustain its population for 100 years with sizes similar to simulations without weevil predation. Furthermore, uncertainty analysis showed that the mean MSI of the population decreased over a 100-year period without weevil predation, and this trend was exacerbated by the presence of weevil predation.

The giant air plant of Florida has been declared endangered due to predation from an invasive weevil. These plants are incredibly important to the biodiversity of Florida; they have a water retaining tank within which live ecosystems of thousands of individuals, some that are completely reliant on these types of micro ecosystems. The giant air plants have only a single reproduction event during their lifespans, and the predatory weevils target the reproductive portion of the plants. This has led to the population reproducing earlier, when they are of a smaller size. Our computer simulations have shown that, even in the absence of the weevil, the plants continue to follow this earlier reproduction trend, putting their long-term survival at risk.

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