Human colonization of islands has resulted in the reduction or loss of many native species, and the introduction of non‐native species, producing novel ecosystems. The impacts of these changes on mutualistic plant–animal interactions have received considerable attention, but the potential effects on some antagonistic interactions, such as seed predation, are less thoroughly understood, and often overlooked. Using three archetypal island groups—New Zealand, the Mascarenes and Hawaiʻi—we compare the taxonomic richness and functional diversity of vertebrate seed predators from prehuman and contemporary ecosystems. We scored species on several traits relevant to seed predation, then clustered species into functionally similar groups using hierarchical clustering. These archipelagos once supported between 19 and 24 species of exclusively avian seed predators (representing two to four orders) ranging from large, flightless herbivores to small, volant finches and parrots. Following human arrival, 63%–89% of these species went extinct, and between 12 and 23 non‐native seed predators were introduced. Contemporary seed predator faunas consist of between 14 and 26 species (representing six to seven orders), dominated by non‐native granivorous birds and omnivorous mammals. Our results reveal several examples in which non‐native species may be functionally similar to extinct seed predators, but most non‐native species are functionally different from extinct species, and therefore may be introducing novel seed predation pressures for insular ecosystems. Mammalian seed predators are especially functionally different from the native avian seed predators, as their teeth and widespread habitat distribution allow them to destroy a more diverse range of seeds, including the largest seeds. We highlight the need to understand how these altered seed predator communities are affecting native plant populations, particularly in the context of reduced pollination and seed dispersal. More broadly, we argue that antagonistic interactions are an integral part of any ecosystem, and therefore must be understood if we are to achieve more holistic restoration frameworks for insular ecosystems. A free Plain Language Summary can be found within the Supporting Information of this article.

Often the mutualistic roles of extinct species are inferred based on plausible assumptions, but sometimes palaeoecological evidence can overturn such inferences. We present an example from New Zealand, where it has been widely assumed that some of the largest-seeded plants were dispersed by the giant extinct herbivorous moa (Dinornithiformes). The presence of large seeds in preserved moa gizzard contents supported this hypothesis, and five slow-germinating plant species () with thick seedcoats prompted speculation about whether these plants were adapted for moa dispersal. However, we demonstrate that all these assumptions are incorrect. While large seeds were present in 48% of moa gizzards analysed, analysis of 152 moa coprolites (subfossil faeces) revealed a very fine-grained consistency unparalleled in extant herbivores, with no intact seeds larger than 3.3 mm diameter. Secondly, prolonged experimental mechanical scarification of and seeds did not reduce time to germination, providing no experimental support for the hypothesis that present-day slow germination results from the loss of scarification in moa guts. Paradoxically, although moa were New Zealand's largest native herbivores, the only seeds to survive moa gut passage intact were those of small-seeded herbs and shrubs.

Understanding marginal habitat use by invasive species is important for predicting how distributions may change under future climates. We investigated the influence of food availability and temperature on ship rat (Rattus rattus) distribution and density across a forested elevational gradient in New Zealand by measuring ship rat demographics following a beech (Nothofagaceae) mass seeding event (‘mast’) at three elevation bands (20–80, 400–500, 800–900 m asl). We tested whether declining food availability limits rat populations at the highest elevation band post-mast by experimentally increasing food abundance above baseline food availability. When our study started 4 months post-seedfall, rats at mid- and low- elevations were at high densities (11.4–16.5 ha−1). Rats at higher elevations were barely detectable, but densities peaked (9.4 ha−1) 10 months post-seedfall, with the initial increase possibly driven by immigration from lower elevations. All populations declined sharply over the next year. Supplementary feeding at high elevation increased survival, recruitment, and density of rats through winter, 16 months post-seedfall, relative to unfed grids, suggesting food limitation. However, both fed and non-fed populations declined to zero by the following spring, perhaps due to stoat (Mustela erminea) predation. Our results suggest that low food availability plays a significant role in restricting rats from cool, high elevation environments. The variation in the timing and magnitude of ship rat responses to the pulsed resource across the gradient also highlights the importance of initial population size and spatial processes as factors modulating ship rat responses to pulsed resources across a landscape.

Formulations of glyphosate-based herbicides continue to dominate the global herbicide market, while there continue to be concerns regarding the impact of this herbicide on non-target organisms. Research also indicates that the additives within certain glyphosate formulations, such as surfactants, are actually more toxic than the glyphosate active ingredient alone. Concerns arise in particular when glyphosate formulations are proposed for vegetation control in areas inhabited by rare or threatened species. Although the effect of glyphosate on birds and mammals is well studied, reptiles remain neglected in ecotoxicological studies. We investigated whether dermal exposure to two different commercial glyphosate formulations affected performance measures in the New Zealand common skink (Oligosoma polychroma). Fifty-eight skinks were each placed in a box of straw to simulate field conditions and sprayed once with Agpro Glyphosate 360, Yates Roundup Weedkiller (both at the label-specified concentrations of 144 mg glyphosate per 1 L water), or water (control). Agpro Glyphosate 360 contained ethoxylated tallow amine at a concentration of <200 g/L, while the surfactant within Yates Roundup Weedkiller was unknown. Following treatment skinks were kept in captivity and sampled for selected temperature and mass over a four-week period. Neither glyphosate formulation had a significant impact on mass. However, skinks treated with Yates Roundup Weedkiller selected significantly higher temperatures across 3 weeks following exposure. This heat-seeking behaviour could be a fever response to increase metabolism and thereby counteract physiological stress.

Understanding the mutualistic services provided by species is critical when considering both the consequences of their loss or the benefits of their reintroduction. Like many other Pacific islands, New Zealand seed dispersal networks have been changed by both significant losses of large frugivorous birds and the introduction of invasive mammals. These changes are particularly concerning when important dispersers remain unidentified. We tested the impact of frugivore declines and invasive seed predators on seed dispersal for an endemic tree, hinau Elaeocarpus dentatus, by comparing seed dispersal and predation rates on the mainland of New Zealand with offshore sanctuary islands with higher bird and lower mammal numbers. We used cameras and seed traps to measure predation and dispersal from the ground and canopy, respectively. We found that canopy fruit handling rates (an index of dispersal quantity) were poor even on island sanctuaries (only 14% of seeds captured below parent trees on islands had passed through a bird), which suggests that hinau may be adapted for ground‐based dispersal by flightless birds. Ground‐based dispersal of hinau was low on the New Zealand mainland compared to sanctuary islands (4% of seeds dispersed on the mainland vs. 76% dispersed on islands), due to low frugivore numbers. A flightless endemic rail (Gallirallus australis) conducted the majority of ground‐based fruit removal on islands. Despite being threatened, this rail is controversial in restoration projects because of its predatory impacts on native fauna. Our study demonstrates the importance of testing which species perform important mutualistic services, rather than simply relying on logical assumptions.

The kereru (Hemiphaga novaeseelandiae) is a large fruit pigeon that in New Zealand is an important seed disperser for native plant species. However, little is known about recent changes in kereru densities and how these changes might affect seed dispersal services. We used long-term kereru counts and seedfall trap data from Pelorus in Marlborough to measure trends in bird abundance and seed dispersal. Using monthly kereru counts from 1983-1989 and 2002-2006, we found that counts significantly decreased between the two decades. Most of this decline was driven by changes in the seasonal abundance of kereru: a pronounced late-winter/spring peak in numbers in the 1980s had almost vanished by the 2000s. The late-winter/spring increase in kereru in the 1980s was probably driven by kereru moving into the area to feed on lowland foliage. Therefore, the reduction of late-winter/spring kereru in the 2000s could be driven by either a change in regional movement patterns or an authentic decline in the kereru population. Seedfall data for six fleshy-fruited trees (tawa Beilschmiedia tawa, miro Prumnopitys ferruginea, matai Prumnopitys taxifolia, hinau Elaeocarpus dentatus, rimu Dacrydium cupressinum, and kahikatea Dacrycarpus dacrydioides) from 1986-1990 and 2004-2010 allowed estimation of the percentage of each fruit crop handled by frugivores (an index of dispersal quantity). We found that the percentage of seeds handled by frugivores was higher in the 2000s than in the 1980s for tawa, and lower for matai. Seed handling rates were unchanged between the two decades for miro, hinau, rimu, and kahikatea. Over this time period there was no overall worsening in dispersal quantity between the two decades, probably because kereru numbers did not change significantly during the autumn fruiting season, and because other birds could be important dispersers for smaller-seeded species.

Human presence is becoming increasingly ubiquitous, but the influence this has on the seed dispersal services performed by frugivorous animals is largely unknown. The New Zealand weka ( Gallirallus australis ) is an inquisitive flightless rail that frequently congregates in areas of high human use. Weka are important seed dispersers, yet the seed dispersal services they provide are still poorly understood. We estimated seed dispersal distances of weka for two plant species ( Prumnopitys ferruginea and Elaeocarpus dentatus ) and tested how human interaction affected these dispersal distances. We estimated weka seed dispersal distances by combining GPS data from 39 weka over three sites with weka seed retention time data in a mechanistic model. The mean seed retention times were extremely long (38–125 h). Weka were highly effective dispersers, dispersing 93–96% of seeds away from parent canopies, and 1% of seeds over 1 km. However, we found evidence of a significant human impact on the seed dispersal distances of weka, with birds occupying areas of high human use performing 34.8–40.9% shorter distances than their more remote counterparts. This represents an example of cryptic function loss, where although weka are still present in the ecosystem, their seed dispersal services are impaired by human interaction.

There is increasing interest in restoring native predators in order to regulate ecosystems and maintain biodiversity, but predator reintroductions are still controversial for complex social and ecological reasons. Few studies have examined predator restoration on islands or in ecosanctuaries, where highly endemic faunas have typically undergone precipitous declines and extinctions due to novel invasive predators, and translocations are used to restore species. Currently in New Zealand, discussions regarding predators typically focus on introduced mammalian pests, and the importance of native predators is frequently overlooked. We present a case study of the mesopredatory New Zealand weka (Gallirallus australis), a threatened flightless rail that provokes controversy among restoration practitioners due to concerns that it may decrease populations of other threatened species. We (1) review studies of weka diet and impacts on native and exotic fauna; (2) contrast prehistoric and contemporary predation webs focused on weka; and (3) consider the role of biocultural approaches in the management and restoration of socio-ecological systems with weka. Weka are opportunistic omnivores that can include vertebrates in their diet, and on small islands where weka can reach high densities there is some evidence that they may limit some prey populations. However, very few manipulative experimental studies measuring effects of weka on native species have been carried out, and such studies would be extremely valuable. Weka also consume invasive rodents and, if they obtain a sufficiently high density, may provide benefits in ecosanctuaries by limiting invasive mice populations. Māori historically harvested weka, and such harvest may now valuably limit weka numbers at certain island or ecosanctuary sites, perhaps replacing the effect of extinct avian competitors and apex predators. How weka and other native predators should be managed on islands depends on the value placed on ecosystem restoration, species-focused conservation, or biocultural enrichment.