Effects of urbanisation on medium-sized and large mammals in the lowlands around Mt. Tsukuba

Abstract

Urbanisation is ongoing worldwide and has various effects on wildlife. The changes in mammal communities caused by urbanisation are important for biodiversity conservation because mammals are large, consume large amounts of energy, and tend to occupy higher positions in trophic webs than other species classes. Furthermore, in urban and rural landscapes, conflicts between mammals and humans, such as damage to agricultural crops or road kills, are increasing. The city of Tsukuba in Ibaraki Prefecture, Japan, is undergoing rapid urbanisation. Tsukuba is characterised by a large continuous forest around Mt. Tsukuba and highly fragmented forests in urban areas. This ecological setting allows us to examine the effects of urbanisation on mammal communities at a relatively small spatial scale. With this advantage, we used camera trap surveys to investigate the variation in mammal species composition, diversity, and diel activity from the foothills of Mt. Tsukuba to urbanised lowland areas. From July to November 2019, we conducted camera trap monitoring at 24 forest sites. At each site, a camera was set in a place with relatively little groundcover vegetation to maximise the consistency of detection rates. Camera data were collected monthly and the captured 15-second-long videos were analysed. The 24 sites were classified by forest continuity (continuous or fragmented), amount of vehicular traffic (high, medium, or low), and vegetation type (natural, semi-natural, or artificial). The relationships between these factors and the number of records per species were examined using a generalised linear model (GLM). The number of camera trap days per site averaged 81 and 525 video files of 10 mammal species were obtained. Wild boar (Sus scrofa), Japanese badger (Meles meles), Japanese marten (Martes melampus), and Japanese squirrel (Sciurus lis) were recorded mainly in continuous forests. Raccoon dog (Nyctereutes procyonoides), Japanese hare (Lepus brachyurus), and masked palm civet (Paguma larvata) were recorded in both fragmented and continuous forests. The common raccoon (Procyon lotor), an introduced species, was recorded only in fragmented forests. The GLM analyses revealed that forest continuity had significant positive effects on the number of records of wild boar and masked palm civet. The amount of vehicular traffic had significant negative effects on the number of records of wild boar and Japanese marten, but positive effects on those of raccoon dogs and common raccoons. Before the study, we expected that the presence of natural and semi-natural forests would have positive effects on the abundances of all mammals, but the common raccoon was captured significantly more frequently in artificial forests than in natural or semi-natural forests. Species accumulation curve analysis demonstrated that forest fragmentation markedly reduced native species richness. The diel activity patterns of raccoon dogs differed significantly with differences in forest continuity, amount of vehicular traffic, and vegetation type, whereas those of Japanese hare and masked palm civet did not. In summary, urbanisation strongly influenced species composition, diversity, and diel activity, but the response patterns varied considerably among species.