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Seabirds influence island ecosystems through nutrient additions and physical disturbance. These influences can have opposing effects on an island's invertebrate predator populations. Spiders (order: Araneae) are an important predator in many terrestrial island ecosystems, yet little is known about how seabird presence influences spider communities at the intraisland scale, or how they respond to seasonality in seabird colony attendance.We investigated the effects of seabird presence and seasonality on ground‐active spider community structure (activity‐density, family‐level richness, age class, and sex structure) and composition at the family‐level across five short‐tailed shearwater breeding islands around south‐eastern Tasmania, Australia. Using 75 pitfall traps (15 per island), spiders were collected inside, near, and outside seabird colonies on each island, at five different stages of the short‐tailed shearwater breeding cycle over a year. Pitfall traps were deployed for a total of 2674 days, capturing 1592 spiders from 26 families with Linyphiidae and Lycosidae the most common. Spider activity‐density was generally greater inside than outside seabird colonies, while family‐level richness was generally higher outside seabird colonies. For these islands, seabird breeding stage did not affect activity‐densities, but there were some seasonal changes in age class and sex structures with more adult males captured during winter. Our results provide some of the first insights into the spatial and temporal influences seabirds have on spider communities. We also provide some of the first records of spider family occurrences for south‐eastern Tasmanian islands, which will provide an important baseline for assessing future change. [ABSTRACT FROM AUTHOR]

[Display omitted] • Assessing ecosystem level response to invasive mammal eradication is challenging. • Nitrogen stable isotopes may provide a useful indicator of recovery on seabird islands. • Numerous confounding factors influence isotope ratios. • We show the importance of considering what, when and where sampling is undertaken. Invasive mammal eradications are widely used for managing island ecosystems. However, tracking the outcomes of such large-scale, whole ecosystem projects is challenging and costly, and monitoring all components of an ecosystem is near impossible. Instead, indicators of ecosystem change may provide more practical and integrated measures of ecosystem response to eradications. As high-order marine predators, seabirds subsidise island ecosystems with nutrients isotopically enriched in nitrogen. Invasive mammals have caused a global decline of seabirds on islands, reducing this nutrient subsidisation. Following eradications, nitrogen stable isotope analysis may provide a useful and resource-efficient indicator of ecosystem functional change on eradicated islands. However, isotope ratios are affected by a myriad of factors, with potential sources of variation being introduced by spatial and temporal variation in sampling, and within and between different taxa and ecosystem components. To correctly attribute isotopic change to post-eradication ecosystem function change, these confounding variables need to be understood. To address this need, we analysed stable isotopes of nitrogen in soil, plant, spider, and seabird guano samples collected at different distances from seabird colonies and at different stages of the short-tailed shearwater breeding cycle on six island sites around south-eastern Tasmania, Australia. Across these cool, temperate islands we detected no temporal variability in δ15N throughout the breeding season. However, there was notable spatial variability in δ15N values. The effects of seabird-derived nutrient subsidisation were highly localised with high δ15N values found inside seabird colonies and then rapidly decreasing from the colony boundary. Higher δ15N values also occurred in areas of higher burrow density within a colony. Variability in δ15N values also existed both within and between ecosystem components. Our results highlight the importance of context dependency when using ecological indicators and have important implications for the design, implementation and interpretation of studies employing stable isotopes as indicators for ecosystem change. We provide recommendations for designing future stable isotope studies on seabird islands. [ABSTRACT FROM AUTHOR]

Summary Introduced rabbits have severely impacted the terrestrial ecosystem of sub-Antarctic Macquarie Island. Here we describe first observations of rapid recovery of an important plant species following the commencement of a vertebrate pest eradication plan. The tussock grass Poa foliosa, a major component of the Macquarie Island landscape, has been severely impacted by rabbit grazing with large-scale reductions in cover across the island observed at times over the last 50 years. Preliminary aerial baiting for rabbits and rodents commenced in winter 2010, and within 6 months, we observed substantial regrowth of tussock grass. The rapid re-emergence of this grass over such a short time period following localised removal of rabbits has positive implications for the island's recovery and provides insight for restoration monitoring. [ABSTRACT FROM AUTHOR]

The impact of introduced ship rats (Rattus rattus) on recruitment of the megaherbPleurophyllum hookeriBuchan. (Asteraceae) was examined on subantarctic Macquarie Island, an island with no extant native terrestrial vertebrates.Pleurophyllum hookeri(Asteraceae) forms a dominant component of the Macquarie Island vegetation and is restricted to the subantarctic. The Macquarie Island population ofP. hookeriis the most extensive and intact. Introduced ship rats (Rattus rattus) are well established in tall tussock grassland of Macquarie Island. We detected rat activity for the first time withinP. hookeriherbfields, in autumn 2000. We found rats were destroying up to 90% of racemes. By excluding rats from caches of inflorescences that they had formed, we found they were having a significant negative effect on initial recruitment and seedling survival within the caches. However, because of high seedling mortality after 1 year, there was no sustained impact of the exclosures onP. hookeriseedling density. [ABSTRACT FROM AUTHOR]