Climate driven seasonal patterns in an ant–plant–herbivore interaction

How do seasonal changes in climate influence ecological interactions in an extrafloral nectary‐bearing plant community? Find out in recently published Journal of Ecology paper by Calixto et al.

Author Kleber Del-Claro explains how climate can directly and indirectly impact ant–plant–herbivore interactions, and how we can better understand these changes by considering plant phenology over time.

Mutualistic interactions are ubiquitous in nature, yet their outcomes are highly variable across time and space. Identifying the biotic and abiotic drivers of such spatial and temporal variation has been a central goal in ecology and evolutionary biology during last decades. Some studies have demonstrated that variability in biotic and abiotic factors are fundamental drivers of spatiotemporal variation in mutualistic interactions. However, most research in this area has attempted to identify spatial drivers at different scales of variation, with a smaller area of emphasis dedicated to understanding the temporal dynamics.

Figure 1 – Ectatomma tuberculatum ant foraging on extrafloral nectaries of Lafoensia pacari plant in the Brazilian savanna, Cerrado. This mutualistic interaction is based on the supply of extrafloral nectar (carbohydrate-rich liquid) by plants and defense against herbivores by ants.

Interactions between ants and plants bearing extrafloral nectaries (EFNs) (Fig. 1) are among the most common mutualisms in Neotropical regions. Plants secrete extrafloral nectar, a carbohydrate-rich food that attracts ants, which in return protect plants against herbivores. This ant-plant mutualism is subjected to temporal variation, in which abiotic factors can drive the establishment and frequency of such mutualistic interaction. However, studies investigating how abiotic factors (e.g., climate) directly and indirectly influence ant-plant-herbivore interactions are incipient.

In this study, we investigated direct and indirect (via plant phenology) effects of temperature and rainfall on ant-plant-herbivore interactions. To address these goals, each month we estimated six plant phenophases (newly flushed leaves, fully-expanded leaves, deciduousness, floral buds, flowers, and fruits), the activity of EFNs and abundance of ants and herbivores in 18 EFN-bearing plant species growing in a markedly seasonal region (the Brazilian Cerrado) during a complete growing season. Our main hypothesis was that due to the strong climate seasonality of the Brazilian Cerrado, plants produce active EFNs at the beginning of the rainy season, when new leaves flush, resulting in the highest abundance of nectar-feeding ants and herbivores (i.e., temporal variation of ant-plant-herbivore interactions).

Figure 2. Annual peaks in six plant phenophases, the activity of extrafloral nectaries (EFNs), and the abundance of ants and herbivores in 18 EFN-bearing plant species in the Brazilian Cerrado. Arrow position represents the mean angle (mean month) where arrow length represents the length of mean vector (r). Rainy season (in blue) – October to March; Dry season (in gray) – April to September. Statistical results are depicted in Table 1.

Our results showed that (i) there were marked seasonal patterns in all plant phenophases, EFN activity, and the abundance of ants and herbivores; (ii) the peak of EFN activity and ant and herbivore abundance simultaneously occurred at the beginning of the rainy season, when new leaves flushed; and (iii) rainfall directly and indirectly (via changes in the production of new leaves) influenced EFN activity and this in turn provoked changes in ant abundance (but not on herbivores) (Fig. 2). Overall, our results build toward a better understanding of how climate drives seasonal patterns in ant-plant-herbivore interactions, explicitly considering plant phenology over time.

Kleber Del-Claro Universidade de São Paulo & Universidade Federal de Uberlândia, Brazil

Read the full paper online: Climate seasonality drives ant–plant–herbivore interactions via plant phenology in an extrafloral nectary‐bearing plant community by Calixto et al. (2020).

You can also read our recent blog, which describes related research from Del-Claro, Calixto and co-authors: Optimal Defense Theory in an ant–plant mutualism

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