Effects of possum browsing on northern rata, Orongorongo Valley, Wellington, New Zealand

Cowan, P. E.; Chilvers, B. Louise; Efford, Murray G.; McElrea, G. J.

doi:10.1080/03014223.1997.9517530

Cited by 12 publications

(4 citation statements)

References 4 publications

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“…Insects damaged all mistletoe plants in the present study during most seasons, whereas possums browsed a much smaller proportion of the plant population but inflicted severe defoliation over a short time period. Other studies are consistent with these relative patterns of vertebrate and invertebrate herbivory both on mistletoes (Wilson 1984; Owen 1993) and other plant species (Meads 1976; Cowan et al 1997b). Insect browse may constitute a predictable stress for some plants, whereas vertebrate damage is much less predictable, more concentrated and potentially more detrimental to plant health.…”

Section: Discussionsupporting

confidence: 60%

Heterogeneity in vertebrate and invertebrate herbivory and its consequences for New Zealand mistletoes

Sessions¹,

Kelly²

2001

Austral Ecology

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Vertebrate herbivores generally have greater effects than invertebrates on plants. However, few studies have investigated the effects of both invertebrate and vertebrate herbivores on a single plant species. In New Zealand, nationwide declines in mistletoe populations have often been attributed to possum herbivory, but never to insect herbivory. The main goal of the present study was to document levels of vertebrate and invertebrate herbivory on endemic New Zealand mistletoe plants to suggest whether herbivory is leading to mistletoe decline. In the present study, the annual amount of leaf loss from herbivory by the brushtail possum (Trichosurus vulpecula), insect herbivory and leaf abscission were measured in two populations each of three mistletoe species (Alepis flavida, Peraxilla colensoi, and Peraxilla tetrapetala, Loranthaceae). In two populations of each species from February 1997 to February 1998, abscission accounted for the most leaf loss (range 10–84% of total mean leaf area, mean 33%), whereas insects and possums usually removed small and similar amounts (less than 3%). Possum browse caused large amounts of abscission in only one population (A. flavida at Eglinton). Observed possum browse was more heterogeneous than insect browse among branches within a plant (possum coefficient of variation = 2.63, insect CV = 1.98, P < 0.001), among plants in a population (possum CV = 2.15, insect CV = 0.69, P < 0.001), and between populations (possum CV = 1.36, insect CV = 1.09). Moreover, insects damaged 100% of the study plants but never removed more than 16% of leaf area on a single plant, whereas possums only browsed 32% of the study plants but severely defoliated some plants. Thus, while the mean amount of biomass removed across a population may have important consequences for mistletoe survival, the effect of possums on mistletoe populations may also depend on the heterogeneity of browse among individuals in the population.

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Section: Discussionsupporting

confidence: 60%

Heterogeneity in vertebrate and invertebrate herbivory and its consequences for New Zealand mistletoes

Sessions¹,

Kelly²

2001

Austral Ecology

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“…As immigration by possums following population control has consistently been shown to be by young animals, and mostly males [ 30 ], we expected a priori that the invading possum demographic would largely be made up of sub-adult males dispersing into new territory. However, of the eight invaders captured to 1 July 2021, only one was a sub-adult male, five were adult males and two were adult females.…”

Section: Discussionmentioning

confidence: 99%

“…Repeated, ongoing application of aerial 1080 is the most common approach used at large (>10,000 ha) scale on the New Zealand mainland to suppress pest populations to low numbers [ 24 , 28 ]. While this cyclical approach benefits many native species [ 29 ], the costs are ongoing and results are limited by the cyclical recolonisation and breeding of pest species [ 30 ].…”

Section: Introductionmentioning

confidence: 99%

“…Possum reinvasion can be reduced by selecting sites that utilise natural barriers to movement, such as alpine ranges and cold, fast rivers [ 30 , 34 , 35 ]. Here, we present a case study illustrating this approach to possum elimination at the >11,000 ha scale in the Perth River Valley, South Westland, New Zealand, focusing on detection and removal.…”

Section: Introductionmentioning

confidence: 99%

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Targeted Mop up and Robust Response Tools Can Achieve and Maintain Possum Freedom on the Mainland

Cook

Mulgan

2022

Animals

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Unfenced sites on mainland New Zealand have long been considered impossible to defend from reinvasion by possums, and are thus unsuitable for eradication. In July 2019, we began eliminating possums from 11,642 ha (including approximately 8700 ha of suitable possum habitat) in South Westland, using alpine rivers and high alpine ranges to minimise reinvasion. Two aerial 1080 (sodium fluoroacetate) applications, each with two pre-feeds, were used. Here, we detail the effort to mop up existing possums and subsequent invaders in the 13 months following the aerial operation. Possums were detected and caught using a motion-activated camera network, traps equipped with automated reporting and a possum search dog. The last probable survivor was eliminated on 29 June 2020, 11 months after the initial removal operation. Subsequently, possums entered the site at a rate of 4 per year. These were detected and removed using the same methods. The initial elimination cost NZD 163.75/ha and ongoing detection and response NZD 15.70/ha annually. We compare costs with possum eradications on islands and ongoing suppression on the mainland.

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Thresholds in plant–herbivore interactions: predicting plant mortality due to herbivore browse damage

et al. 2012

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Patterns of herbivore browse at small scales, such as the rate of leaf consumption or plant preferences, drive the impact of herbivores on whole-plant processes, such as growth or survival, and subsequent changes in plant population structure. However, herbivore impacts are often non-linear, highly variable and context-dependent. Understanding the effect of herbivores on plant populations therefore requires a detailed understanding of the relationships that drive small-scale processes, and how these interact to generate dynamics at larger scales. We derive a mathematical model to predict annual rates of browse-induced tree mortality. We model individual plant mortality as a result of rates of foliage production, turnover and herbivore intake, and extend the model to the population scale by allowing for between-tree variation in levels of herbivore browse. The model is configurable for any broadleaved tree species subject to vertebrate or invertebrate browse, and is designed to be parameterized from field data typically collected as part of browse damage assessments. We parameterized and tested the model using data on foliage cover and browse damage recorded on kamahi trees (Weinmannia racemosa) browsed by possums (Trichosurus vulpecula) in New Zealand forests. The model replicated observed patterns of tree mortality at 12 independent validation sites with a wide range of herbivore densities and browse damage. The model reveals two key thresholds; in plant foliar cover, indicating when individual trees may be at high risk from browse-induced mortality, and in herbivore intake, leading to high rates of mortality across the whole population.

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Effects of possum browsing on northern rata, Orongorongo Valley, Wellington, New Zealand

Cited by 12 publications

References 4 publications

Heterogeneity in vertebrate and invertebrate herbivory and its consequences for New Zealand mistletoes

Heterogeneity in vertebrate and invertebrate herbivory and its consequences for New Zealand mistletoes

Targeted Mop up and Robust Response Tools Can Achieve and Maintain Possum Freedom on the Mainland

Thresholds in plant–herbivore interactions: predicting plant mortality due to herbivore browse damage

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