Association patterns of swollen‐thorn acacias with three ant species and other organisms in a dry forest of Panama

Ants in obligate defense mutualisms with plants protect them against potentially damaging organisms. In the swollen‐thorn acacias, organisms linked to the plant inform about the interaction between the tree and the resident ant colony. Some organisms coexist with the aggressive mutualistic ants: specialized herbivores and organisms using the enemy‐free space. Conversely, trees inhabited by non‐defending ants usually hold a greater load of generalist herbivores and are avoided by organisms looking for the ant protection. We aimed to elucidate the association type between swollen‐thorn acacias (Vachellia collinsii) and the almost unstudied Pseudomyrmex simulans ants from Panama. We compared the presence of non‐ant organisms on trees inhabited by P. simulans, a well‐known mutualist (P. spinicola) and a facultative parasite (non‐defending ants; Crematogaster crinosa). We recorded non‐ant organisms (e.g., stem galls, acacia true bugs, spiders) that nest, lay eggs, or live on the trees. Except for stem galls, all other non‐ant organisms were mostly or exclusively found on trees with the mutualists, which is also the most common resident ant. P. simulans is less able to deter galling midges (Cecidomyiidae) than C. crinosa and even less than P. spinicola, because trees with P. simulans were more likely to have galls and in greater densities than on C. crinosa‐trees, and even more than on P. spinicola‐inhabited trees. The mechanism by which the Cecidomyiids occur in greater proportion on trees with P. simulans and C. crinosa is still unknown, but the pattern indicates an herbivory specialization or a potentially obligate weaker defender of the swollen‐thorn acacias. in Spanish is available with online material RESUMEN Las hormigas que viven en mutualismos de defensa obligatorios con plantas las protegen contra organismos potencialmente dañinos. Organismos asociados al mutualismo pueden informar sobre el tipo de interacción entre las hormigas residentes y el árbol. Algunos organismos son capaces de coexistir con las hormigas mutualistas: herbívoros especializados y organismos que anidan en la planta usando el espacio libre de enemigos que crean las hormigas agresivas. Por el contrario, árboles habitados por hormigas que no defienden (i.e. parásitas del mutualismo) usualmente tienen una carga mayor de herbívoros y son evitados para anidar por otros organismos. Intentamos entender el tipo de asociación entre árboles de acacia (Vachellia collinsii) y unas hormigas poco