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<p>The Optimal Defense Hypothesis (ODH) posits that investment in defense is proportional to the value of what is defended, predicting that the most valuable resources should have the strongest defenses. We determined whether an obligate ant-plant mutualism aligns with the predictions of the ODH and tested the impact of sporadic rainfall in this process. Sampling was performed in a tropical deciduous forest on the Yucatán Peninsula, Mexico, on <i>Vachellia globulifera</i> plants and one of their obligate mutualist ant species, <i>Pseudomyrmex ferruginosus</i>. We sampled ant activity before, during, and after an experimental rain event in branches with housing and food rewards (domatia and leaves with nectaries and food bodies) and in branches with only domatia (swollen spines). We found that: (a) before the experimental rain, the number of patrolling events was two-fold higher in branches with spines and leaves compared with branches with only spines, (b) during the experimental rain, ants on branches with spines and leaves stayed on the branch at a higher rate compared to branches with only spines, and (c) right after the experimental rain, while branches with the two types of resources reach levels of ant activity almost identical to those observed before the rain (90%), branches with only spines achieve only 20%. These results are consistent with the ODH, as ants showed greater activity toward the most valuable resources. Moreover, they provided experimental evidence of the impact of sporadic rainfall events on ant-plant mutualisms, suggesting that ant activity on these resources can be resilient to small climatic events.</p>

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The short-term response of ants to sporadic rain events is consistent with the optimal defense hypothesis in an ant-plant mutualism

  • 期刊论文

  • 发表日期：

    2026年7月20日

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  • A. G. Farji-Brener,
  • F. B. Flores,
  • E. René,
  • H. Flores-Hernández,
  • S. Amador-Vargas

摘要

The Optimal Defense Hypothesis (ODH) posits that investment in defense is proportional to the value of what is defended, predicting that the most valuable resources should have the strongest defenses. We determined whether an obligate ant-plant mutualism aligns with the predictions of the ODH and tested the impact of sporadic rainfall in this process. Sampling was performed in a tropical deciduous forest on the Yucatán Peninsula, Mexico, on Vachellia globulifera plants and one of their obligate mutualist ant species, Pseudomyrmex ferruginosus. We sampled ant activity before, during, and after an experimental rain event in branches with housing and food rewards (domatia and leaves with nectaries and food bodies) and in branches with only domatia (swollen spines). We found that: (a) before the experimental rain, the number of patrolling events was two-fold higher in branches with spines and leaves compared with branches with only spines, (b) during the experimental rain, ants on branches with spines and leaves stayed on the branch at a higher rate compared to branches with only spines, and (c) right after the experimental rain, while branches with the two types of resources reach levels of ant activity almost identical to those observed before the rain (90%), branches with only spines achieve only 20%. These results are consistent with the ODH, as ants showed greater activity toward the most valuable resources. Moreover, they provided experimental evidence of the impact of sporadic rainfall events on ant-plant mutualisms, suggesting that ant activity on these resources can be resilient to small climatic events.