Abundance and Dynamics of Small Mammals in New Zealand: Sequential Invasions into an Island Ecosystem Like No Other

Abstract

New Zealand had no people or four-footed mammals of any size until it was colonised by Polynesian voyagers and Pacific rats in c. 1280 AD. Between 1769 and 1920 AD, Europeans brought three more species of commensal rats and mice, and three predatory mustelids, plus rabbits, house cats hedgehogs and Australian brushtail possums. All have in turn invaded the whole country and many offshore islands in huge abundance, at least initially. Three species are now reduced to remnant populations, but the other eight remain widely distributed. They comprise an artificial but interacting and fully functional bottom-up predator-prey system, responding at all levels to interspecific competition, habitat quality and periodic resource pulsing.

Biogeography and History of the Prehuman Native Mammal Fauna of the New Zealand Region

“…This late start did at least mean that successive New Zealand governments could avoid some of the mistakes made by other colonial powers, including the deliberate importation of at least the worst exotic mammalian species that have caused havoc elsewhere. Our acutely vulnerable native bats, birds, lizards, and land-breeding pinnipeds would have been even worse off but for the absence of foxes, squirrels and mink, but they have not escaped many other imported pests including rats, mice, cats, rabbits, mustelids and hedgehogs [5]. The once enormously abundant marine mammals (especially fur seals and commercially important whales), which were once the backbone of early colonial economics, have suffered decades of ruthless human exploitation.…”

“…In such severe solitude, priceless remnants of early experiments in evolutionary adaptation of frogs, lizards and invertebrates, which have been extinguished everywhere else, have been preserved alongside new lineages arising from scattered populations stranded by millions of years of varying sea levels or tectonic uplifts, as reviewed by Tennyson [4]. All land mammals other than bats have been introduced since the mid-18th century [5]. In the surrounding oceans, and in the Antarctic, native faunas evolved independently, far outside human view.…”

The genetic signature left by the range expansion of red foxes in Australia is detectable after more than 80 years of population stability

“…Understanding the origins, dynamics and course of biological invasions can provide clues to the management and eradication of the invaders and the prevention of future incursions (Banerjee et al., 2022; King, 2023; Konečný et al., 2013; Lee, 2002). Yet, reconstructing those processes from historical sources, sometimes well after the invasion has occurred, can be difficult and will generally give only part of the story.…”

The Abundance and Dynamics of Small Mammals and Their Predators: An Editorial

“…Almost all studies were conducted in European countries, with four from Spain [7][8][9][10], two from Lithuania [11,12], one from Greece [13], and one from Latvia [14]. The remaining two studies were conducted in New Zealand [15] and Chile [16]. Regarding the topics covered in this Special Issue, the last two mentioned articles addressed the effects of alien species in ecosystems, three focused on the presence and natural control of potential pest species in agroecosystems, two concerned the historical trends of small mammal populations and the effects on their predators, and one discussed the activity of small mammals along man-made gradients of vegetation affected by predation risk.…”

“…The review by Carolyn King [15] takes a historical approach to the arrival and spread of several alien species in New Zealand. The two islands were accidentally colonized by three species of rats and by the house mouse, and these alien species quickly dispersed because of a lack of competitors and predators.…”