Thirty years of vegetation dynamics in response to a fluctuating rabbit population on sub‐Antarctic Macquarie Island

Abstract

Summary Australia's sub‐Antarctic Macquarie Island is presently undergoing one of the most ambitious vertebrate pest eradication programmes ever undertaken. The anticipated success of this programme will release the island's tundra‐like vegetation from well over a century of grazing and disturbance from House Mouse (Mus musculus), Ship Rat (Rattus rattus) and most significantly European Rabbit (Oryctolagus cuniculus). This study describes results from 30 years of vegetation quadrat monitoring (prior to the most recent and comprehensive pest eradication programme) when lower level pest animal control programmes were underway. Plant species were assigned to one of five distinct functional plant groups: Indigenous short‐lived perennials, Introduced short‐lived perennials, Indigenous perennials rarely grazed by rabbits, Indigenous perennials occasionally grazed by rabbits and Indigenous long‐lived perennials heavily grazed by rabbits, with one species, Agrostis magellanica, analysed as a sixth monospecific group. Results from monthly rabbit counts were used to compare changes in abundance of these six groups under different rabbit populations. It was found that there were three distinct phases of rabbit activity during the study period, indicated by (i) an initial very high count year in 1980–1981, followed by (ii) 20 years of low counts ending in 2001–2002 after which (iii) counts rose to medium/high until the commencement of the eradication programme in 2010–2011. Vegetation composition and progression were distinct for these three rabbit count phases. The first four of the plant functional groups decreased under lower count periods and increased in cover under higher rabbit count periods. Agrostis magellanica appears to respond primarily to interspecies competition and is disadvantaged under extended periods of low rabbit numbers. Indigenous long‐lived perennials heavily grazed by rabbits, which includes the large tussocks and megaherbs, is inversely related to rabbit numbers. During the study period, there has also been an overall decline in plant species richness with average species count per quadrat falling by between 0.6 and 2.7 taxa. This study attempts to address the observed vegetation change from this long‐term monitoring, to discuss other potential contributing factors and to use the results to predict likely future vegetation changes after eradication of vertebrate pests.

Implications of shared predation for space use in two sympatric leporids

“…Intense grazing by rabbits can change the plant species composition, vegetation height, and perceived predation risk, thereby affecting the interaction between hares and rabbits (Bakker, Olff, & Gleichman, ; Shipley, ). For example, a change in the plant species composition could lead to an increase or decrease in preferred food plants available for hares (Kuijper & Bakker, ; Whinam, Fitzgerald, Visoiu, & Copson, ). Moreover, the interspecific interaction between hares and rabbits may also be affected by differences in body size, feeding style, digestive system, and morphology (Bell, ; Prins & Olff, ).…”

“…For example, a change in the plant species composition could lead to an increase or decrease in preferred food plants available for hares F I G U R E 2 Location of the three study areas with fox, hare, and rabbit populations: Vennewater (VW), Koningsbos (KB), and Infiltration area Castricum (ICAS) (Kuijper & Bakker, 2008;Whinam, Fitzgerald, Visoiu, & Copson, 2014). Moreover, the interspecific interaction between hares and rabbits may also be affected by differences in body size, feeding style, digestive system, and morphology (Bell, 1971;Prins & Olff, 1998).…”

Assessing the invasive risk of two non-native Agrostis species on sub-Antarctic Macquarie Island

“…As well as three non-native plants now established on the island (see below), the sealing era left a legacy of feral animals (including cats Felis catus Linnaeus, wekas Gallirallis australis scotti Ogilvie-Grant, ship rats Rattus rattus Linnaeus, mice Mus musculus Linnaeus and rabbits Oryctolagus cuniculus Linnaeus) which have had profound and far-reaching effects on the terrestrial environment (PWS 2007;Scott and Kirkpatrick 2013;Whinam et al 2014;Robinson and Copson 2014). After several campaigns over the past few decades, all feral animals have now been eradicated (PWS 2014).…”

“…It is recognized that Macquarie Island's terrestrial ecosystems are vulnerable to the invasion and establishment of introduced non-native plants due to widespread habitat degradation caused by rabbits, and also changing climatic conditions (Whinam et al , 2014PWS 2009). In recent years, introduced non-natives species in polar ecosystems find less physical and environmental barriers for colonization Convey 2010, 2012).…”

“…As an example, Poa annua has colonized, and largely dominates, nearly all suitable coastal habitats with animal disturbance on Macquarie Island. Moreover, the three established non-native plant species on the island have all spread and become more abundant in the past decade (Whinam et al 2014), although it has been predicted that with recovery of native species and plant communities, all three are likely to decline in importance (Copson and Whinam 2001;Scott and Kirkpatrick 2013;Whinam et al 2014). Of the three species, P. annua is the most invasive on Macquarie Island, although its displacement of native communities is considered to be minor (Frenot et al 2005) and it cannot compete long term with native species in the absence of disturbance (Scott and Kirkpatrick 2013).…”