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Abstract Cooperative interactions may frequently be reinforced by “partner fidelity feedback,” in which high‐ or low‐quality partners drive positive feedbacks with high or low benefits for the host, respectively. Benefits of plant–animal mutualisms for plants have been quantified almost universally in terms of growth or reproduction, but these are only two of many sinks to which a host‐plant allocates its resources. By investigating how partners to host‐plants impact two fundamental plant resources, carbon and water, we can better characterize plant–partner fidelity and understand how plant–partner mutualisms may be modulated by resource dynamics. In Laikipia, Kenya, four ant species compete forAcacia drepanolobiumhost‐plants. These ants differ in multiple traits, from nectar consumption to host‐plant protection. Using a 5‐year ant removal experiment, we compared carbon fixation, leaf water status, and stem non‐structural carbohydrate concentrations for adult ant–plants with and without ant partners. Removal treatments showed that the ants differentially mediate tree carbon and/or water resources. All three ant species known to be aggressive against herbivores were linked to benefits for host‐plant resources, but only the two species that defend but do not prune the host,Crematogaster mimosaeandTetraponera penzigi, increased tree carbon fixation. Of these two species, only the nectivoreC. mimosaeincreased tree simple sugars.Crematogaster nigriceps, which defends the tree but also castrates flowers and prunes meristems, was linked only to lower tree water stress approximated by pre‐dawn leaf water potential. In contrast to those defensive ants,Crematogaster sjostedti, a poor defender that displaces other ants, was linked to lower tree carbon fixation. Comparing the effects of the four ant species across control trees suggests that differential ant occupancy drives substantial differences in carbon and water supply among host trees. Our results highlight that ant partners can positively or negatively impact carbon and/or water relations for their host‐plant, and we discuss the likelihood that carbon‐ and water‐related partner fidelity feedback loops occur across ant–plant mutualisms.
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A soil‐nesting invasive ant disrupts carbon dynamics in saplings of a foundational ant–plant
Abstract Nearly every terrestrial ecosystem hosts invasive ant species, and many of those ant species construct underground nests near roots and/or tend phloem‐feeding hemipterans on plants. We have a limited understanding of how these invasive ant behaviours change photosynthesis, carbohydrate availability and growth of woody plants.We measured photosynthesis, water relations, carbohydrate concentrations and growth for screenhouse‐rearedAcacia drepanolobiumsaplings on which we had manipulated invasivePheidole megacephalaants and nativeCeroplastessp. hemipterans to determine whether and how soil nesting and hemipteran tending by ants affect plant carbon dynamics. In a field study, we also compared leaf counts of vertebrate herbivore‐excluded and ‐exposed saplings in invaded and non‐invaded savannas to examine how ant invasion and vertebrate herbivory are associated with differences in sapling photosynthetic crown size.Though hemipteran infestations are often linked to declines in plant performance, our screenhouse experiment did not find an association between hemipteran presence and differences in plant physiology. However, we did find that soil nesting byP. megacephalaaround screenhouse plants was associated with >58% lower whole‐crown photosynthesis, >31% lower pre‐dawn leaf water potential, >29% lower sucrose concentrations in woody tissues and >29% smaller leaf areas. In the field, sapling crowns were 29% smaller in invaded savannas than in non‐invaded savannas, mimicking screenhouse results.Synthesis. We demonstrate that soil nesting near roots, a common behaviour byPheidole megacephalaand other invasive ants, can directly reduce carbon fixation and storage ofAcacia drepanolobiumsaplings. This mechanism is distinct from the disruption of a native ant mutualism byP. megacephala, which causes similar large declines in carbon fixation for matureA. drepanolobiumtrees.Acacia drepanolobiumalready has extremely low natural rates of recruitment from the sapling to mature stage, and we infer that these negative effects of invasion on saplings potentially curtail recruitment and reduce population growth in invaded areas. Our results suggest that direct interactions between invasive ants and plant roots in other ecosystems may strongly influence plant carbon fixation and storage.
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- PAR ID:
- 10362554
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Ecology
- Volume:
- 110
- Issue:
- 2
- ISSN:
- 0022-0477
- Page Range / eLocation ID:
- p. 359-373
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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