Responses of litter‐dwelling arthropods and house mice to beech seeding in the Orongorongo Valley, New Zealand

Abstract

||This study investigates further the possibility that eruptions of house mice in forests of southern beech (Nothofagus spp ) in New Zealand after mast seedings are triggered by increases in the populations of some arthropods, especially Lepidoptera larvae and spiders that are common foods of mice, rather than by the beech seed It reports on a 5-year study of arthropods of the forest floor in hard beech and silver beech forest in the Orongorongo Valley, near Wellington, in relation to (1) litter and seedfall, and (2) the numbers and diet of mice Litter-feeding larvae of Lepidoptera in both the litter and fermentation layers of the forest floor feed on the fallen male flowers of beech, and most species were more common after heavy flowering of the beeches A few of the common spiders (including Miturga sp , the main spider eaten by mice) were also more abundant after beech seeding Analysis of the long-term records of hard beech seeding, numbers of mice, and numbers of adults of the moth Gymnobathra tholodella (Oecophondae) showed that the number of mice was positively correlated with both the number of beech seeds and the number of moths These results indicate a more complex web of interactions in beech forest than was earlier suggested, but because the intensity of flowering in spring largely determines the numbers of both Lepidoptera larvae and beech seeds, the role of each in the population increase of mice can not be determined

Breeding of house mice and the mast seeding of southern beeches in the Orongorongo Valley, New Zealand

“…Invertebrates, especially Lepidoptera larvae and spiders, are commonly eaten by mice (Fitzgerald et al 1996;Miller & Webb 2001) and were more abundant in the forest in mast years and post-mast years than in non-mast years (Alley et al 2001). In Australian mallee wheatfields invertebrates were eaten significantly more by adult breeding mice than by non-breeding ones (Tann et al 1991).…”

“…Lepidoptera larvae were abundant in the litter of hard beech in summer of a mast year, but in silver beech litter larvae were most common in spring and autumn. The abundance of different species of invertebrates also varied between the two sites (Dugdale 1996;Alley et al 2001;unpubl. results).…”

“…We therefore consider it unlikely that consumption of seed by mice explains enhanced breeding in the summer of mast years. Lepidoptera larvae and spiders became abundant in hard beech litter in December (Alley et al 2001;unpubl. results); their continuing availability through summer may explain stronger breeding by mice in summer of mast years.…”

“…A distinction has been made, based on the presence or absence of beech trees at the trap sites, between 34 "beech" trap sites and 82 podocarp/ hardwood ("podocarp") trap sites (Choquenot & Ruscoe 2000;Alley et al 2001). Mice were, overall, caught fairly evenly at the two types of site (13.6 mice/beech trap site, 16.8 mice/podocarp trap site).…”

“…Some feed directly on fallen male beech flowers, whose biomass equals that of the seeds that fall later. These larvae, and some other arthropods, are important prey of mice and increase after beech flowering (Alley et al 2001). Under this view, arthropods provide abundant high-protein food that enables mice to breed and survive better in mast years.…”