Competition-colonization dynamics of spore-feeding beetles on the long-lived bracket fungi Ganoderma in New Zealand native forest

Abstract

We investigated the competition–colonization dynamics of three species of spore-feeding beetles on wood-decaying bracket fungi, Ganoderma spp., in New Zealand. One beetle species (Holopsis sp. 1) was a pore-tube specialist hypothesized to be superior in exploitative competition; the other two (Zearagytodes maculifer and Holopsis sp. 2) were surface grazers. We surveyed beetle abundance, daily spore release per square centimetre, pore surface area, and environmental variables over 30 patches (sporocarps) monthly for one year. We constructed a competitive-interaction web by fitting models to the cross-sectional resource–multiconsumer data. We compared flight behaviour and the associated physiological traits of beetles in wind tunnel experiments, and morphological characters. An examination of the competition–colonization dynamics found (1) the competitive equivalence of Holopsis sp. 1 to Z. maculifer and superiority to Holopsis sp. 2; (2) a reduced population persistence time of Z. maculifer that results from the dominance of Holopsis sp. 1; (3) the dominance of Z. maculifer and Holopsis sp. 1 in larger patches and that of Holopsis sp. 2 in smaller patches; (4) a greater spatial extent of population synchrony in Z. maculifer than in the Holopsis spp.; and (5) more frequent departures (takeoffs) of Z. maculifer than of Holopsis spp., concordant with its greater development of flight muscles and longer hindwing. These beetles may coexist through two types of spatial niche partitioning, each of which explains the pairwise coexistence of competitors but not the coexistence of the three species: Z. maculifer can evade competition with Holopsis sp. 1 by flying frequently or strongly to colonize distant patches, whereas Holopsis sp. 2 can dominate only in smaller and newly emergent patches until the arrival of Holopsis sp. 1.