competition

Cats (Felis catus) are among the most damaging invasive predators in the world, and their impacts in Aotearoa New Zealand (NZ) are particularly severe. However, unlike the invasive predators that are targeted for eradication under the Predator Free NZ initiative, cats are also highly valued by people and therefore will likely remain widespread in NZ for the foreseeable future. This raises the question of how to manage the impacts of cats, which include predation, competition, and disease affecting native species, livestock, and humans.

Recent advances in the control of mammalian predators have begun to reveal interspecific competition as a key driver in the structure of New Zealand forest bird communities once predation pressure is reduced. We present evidence that, when at high densities, South Island robins (Petroica australis) may be responsible for declines in a suite of smaller native and introduced songbird species. Bird surveys undertaken on 47 islands in Breaksea Sound and Dusky Sound, Fiordland, during 1974 to 1986, were repeated on the same islands in 2016 or 2019.

Many tree fern taxa have a skirt, an encircling structure of persistent dead fronds or stipes around the growing crown at the top of the trunk. Page and Brownsey (1986) hypothesised that the function of these skirts was to protect tree ferns against damage from large epiphytes, hemiepiphytes, and climbing plants. Tree fern trunks provide both suitable establishment surfaces for a range of woody epiphytes and hemiepiphytes in New Zealand, as well as attachment surfaces for climbing rātā (Metrosideros spp.).

It is common practice in New Zealand dryland areas to chemically or mechanically control invasive woody weeds, including Scotch broom (Cytisus scoparius). Such weed control is not always effective in achieving the often implicit aim of advancing the restoration of indigenous woody vegetation. We used a field experiment on a braided river terrace on the Canterbury Plains to test how five different management treatments of broom cover affected the germination, survival and growth of six indigenous tree and shrub species in a dryland setting.

Ship rats (Rattus rattus) were removed from sites on Pearl Island, southern Stewart Island, in 2004 and 2005, to test whether they excluded Pacific rats (R. exulans) or Norway rats (R. norvegicus) or both from podocarp-broadleaf forest. As predators can influence habitat use in rodents, Pearl Island was selected because no mammalian predators of rodents are present. Rats were trapped in two other habitats to clarify rat distribution on the island and to obtain samples for stable isotope investigation of food partitioning within habitats.

Possible control options are investigated for the introduced Hieracium weeds, particular problems in South Island high country, New Zealand. In a pot experiment regression of input to output ratios of above ground biomass over successive harvests, from binary mixtures was used to determine the competitive interaction between 13 pasture species and two Hieracium species, H. pilosella and H. praealtum, in a low fertility soil. Treatments also included a factorial of presence or absence of compartments separating root and shoots of species.

Indigenous peoples’ knowledge on changes in wildlife populations and explanations for these changes can inform current conservation and wildlife management systems. In this study, Tūhoe Tuawhenua interviewees provided mātauranga (traditional knowledge) about a repertoire of visual (e.g. decreasing flock size), audible (e.g. less noise from kererū in the forest canopy), and harvest-related (e.g.

Control of one pest species may permit increases in abundance of other pests, thereby reducing the overall net benefit from pest control. We provide evidence that control of introduced possums (Trichosurus vulpecula) may increase ship rat (Rattus rattus) abundance in some New Zealand native forests. Ship rat abundance in a podocarp–hardwood forest was assessed using simple interference indices over 14 years (1990–2004) that included two aerial possum-poisoning operations (1994, 2000).