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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.

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 (The online version contains supplementary material available at 10.1007/s10530-022-02829-z.

The effects of invasive species whose ranges are expanding in response to climate change have the potential to drive a new wave of extinctions in vulnerable species. We explore whether expansion of mammalian predators in New Zealand will lead to the thermal squeeze of a forest avifauna by investigating the mechanisms that have led to recent declines. Analysis of local occupancy across the three main islands between 1969–1979 and 1999–2004 shows that the ranges of predator-vulnerable endemic species are constrained by lowland forest loss and continued to contract to higher-elevation, colder parts of forested mountains. Species that are large, nest in tree cavities, and/or disperse poorly have undergone more rapid recent loss where temperatures are higher, consistent with higher and more constant predation in warmer forested sites being the principal mechanism of recent decline. Warming climate is likely to exacerbate local extinctions of predator-vulnerable species by reducing the extent of cool thermal refugia from continuously high predation pressure below the upper limit of forest. However, warming is unlikely to jeopardise small-bodied, non-cavity-nesting, mobile species, which have had stable or increasing populations in warm sites and largely deforested landscapes. New Zealand will share with Hawai'i the phenomenon of thermal squeeze of endemic forest bird species that is mediated by the changing range of an invasive species, rather than by native species themselves tracking their climatic niches. New Zealand will need to make substantial advances in large-scale predator management in warm forests to halt and reverse forest bird declines.

New Zealand’s native forest bird species with high taxonomic levels of endemism (deep endemics) are more vulnerable to decline than species that arrived and speciated more recently. Here we use national-scale local occupancy data to show that three endemism-linked life-history traits account for greater vulnerability of deep-endemic species in the extant forest avifauna, but also that other, more subtle traits and mechanisms favour rather than hinder endemic persistence. We suggest that these traits together provide a basis for predicting changes in local occupancy following suppression of introduced mammalian predators in different landscapes. Our analyses disentangle the limiting effects of forest area, predation, and food availability for different species. They support understanding that predation by introduced mammals is the primary cause of forest bird declines and limitation today, but suggest that large tracts of native forest are essential for future restoration of endemic forest avifauna, even following suppression of introduced mammalian predators. We predict that with fewer predators (1) deep-endemic species would most successfully and rapidly recover in large tracts of warm forest, (2) scarcity of forest or food would limit recovery in larger-bodied, less mobile species and in mobile cavity-nesters, and (3) interspecific competition would become influential and produce community reassortment.

Kererū declined rapidly following European settlement in New Zealand, and they remain at a reduced density. We assessed three sources of information to test the hypothesis that predation by introduced mammals and abundance of food resources are the two major factors determining kererū abundance across New Zealand. First, we reviewed the literature on factors affecting the vital rates of kererū. This analysis showed that predation is the cause of most nest failures and deaths in kererū. Second, we examined data from a major database of bird sanctuary outcomes across New Zealand to evaluate long-term responses of kererū to intensive pest control at local scales. Kererū detections did not always increase following predator control, which suggests that food supply or forest area may be more important limiting factors at some sanctuaries. Third, to understand the factors underlying temporal and spatial kererū distribution patterns at a national scale, we assessed changes and patterns in kererū local occupancy through time using data from the 1969–1979 and 1999–2004 editions of the Atlas of Bird Distribution in New Zealand. Specifically, we asked (1) whether there have been declines in kererū occupancy between the two Atlases, and (2) how patterns of kererū occupancy relate to indigenous forest cover, temperature, urbanisation, and forest type (podocarp or beech dominated). Kererū occupancy remained stable across the North Island between the two time periods but declined in the South Island. Across both islands and time periods, kererū occupancy decreased significantly as forest cover decreased, which suggests that forest availability is still a major limiting factor across some parts of New Zealand. Overall, our results support previous studies showing that predation by introduced mammals is the primary limiting factor for kererū in forests, but also highlight the importance of forest area and food supply for kererū recovery.

Recognition of conspecifics is an essential precursor of successful mating. Where related species coexist, species discrimination might be important, but because related species are similar, species signal recognition may actually be low. Chemical cues such as cuticular hydrocarbons (CHCs) are frequently used by insects to identify suitable sexual partners. We predicted that New Zealand tree weta (Hemideina spp.), a genus of nocturnal ensiferan Orthoptera that live both allopatrically and sympatrically, use chemical signals from either frass or CHCs to find mates. In a series of six laboratory trials using both H. thoracica and H. crassidens, we found that male tree weta, but not female tree weta, occupied cavities primed with female cuticular cues more often than cavities without. However, males did not discriminate between chemical cues of male and female conspecifics, or between conspecifics and heterospecifics. In field trials, tree weta did not occupy artificial cavities primed with either female frass or female cuticular cues more often than unscented cavities. However, in both trials weta preferentially returned to cavities that had already been occupied earlier in the trials. A final field trial confirmed the presence of mixed species harems during the mating season in one region of sympatry. Our results suggest that selection on sex and species specific chemical cues that could be used to find conspecific mates is weak. Mixed species aggregations suggest that identification of conspecific mating cues has not evolved to be species specific. We infer that for male tree weta, the cost of mating with heterospecifics is likely less than not mating at all.

Alpine invertebrate populations are expected to be highly sensitive to a changing climate because temperature plays an important role in their development, reproduction, and survival. However, high levels of rarity and endemism make it particularly challenging to measure climate effects on this group because interpretation of monitoring data is undermined by high levels of spatial turnover and inter-sample variability. Functional traits may overcome this monitoring challenge by allowing generalisation across taxa based on characters that respond consistently to a changing environment. Here we evaluate whether functional traits respond more consistently and sensitively to changes in environmental conditions at different sites than species diversity metrics. Temperature and physical structure in Chionochloa grassland plots was manipulated using Open-Top-Chamber and fertility treatments, respectively. Pitfall traps were used to sample beetles from four years (2013–2016) during the austral summer at two different altitudes in Takahe Valley, Fiordland. Natural variation between years and sites had a stronger influence on the beetle community compared with temperature and nutrient treatments. The presence of complex interactive effects between treatments, different sites, and different years, indicates that the impact of changes to temperature and nutrient levels are context-specific and that landscape-level variations have a large role on structuring beetle communities. The responses of alpine beetle communities to climate change are likely to be complex, however, trait-based measures may comprise a more sensitive method for detecting generalisable change because they can be pooled over sets of species that appear rarely in the data.

Estimates of vegetation attributes measured by sampling often inform scientific inference, management actions, and policy decisions. However, different sampling methods and sample sizes (i.e. number of plots) can yield significantly different estimates of vegetation attributes. This occurs because the abundance distributions and spatial distributions of species in the plant community influence their probabilities of detection and estimates of their abundances. We predicted that different sampling methods and sample sizes would produce significantly different estimates not only of vascular plant species diversity, but also of indigenous dominance (the level of indigenous influence) in mixed vegetation where indigenous and exotic floras have different abundance or spatial distributions. To test our predictions we applied three sampling methods to 24 plots in grassland and cushion vegetation in a 1058-ha scientific reserve in the Upper Waitaki (Mackenzie) Basin, New Zealand. Our methods sampled ground areas from 0.65 to 400 m 2 , and included two variants of common 'subsampling' approaches, which assessed only discrete subunits within larger plots. Indigenous plant species were both less abundant on average and more spatially-clustered (i.e. less evenly dispersed across plots) than exotic species. The two subsampling methods were less likely to detect less abundant and more spatially clustered species, leading to lower ratios of indigenous to exotic species recorded, and lower estimates of indigenous dominance of composition (% of species indigenous). Numbers of indigenous species accumulated more rapidly with increasing sample size than numbers of exotic species, so that indigenous dominance also increased with the number of plots sampled. We conclude that properly measuring species diversity and indigenous dominance in mixed indigenous-exotic plant communities requires both the searching of sizeable plots and use of rarefaction rather than plot-averaging of statistics. We suggest greater use of rarefaction and more consideration of species' detection probabilities in sampling New Zealand's mixed indigenous-exotic plant communities should improve the reliability, transparency and comparability of measures of diversity and may also provide new ecological insights.

Cold adapted plants, such as cushion plants, may be particularly sensitive to climate warming because of their compact growth form and high branch density. In the oceanic southern hemisphere, cushion communities tend to have large range distributions at low latitudes (sea level to low alpine), thus providing an opportunity to test the effects of temperature on plant morphology and reproduction across gradients. Using Donatia novae-zelandiae as a model species, we compared the leaf morphology, reproduction and responses to warming. Two low-alpine sites (Maungatua (880 m a.s.l.), Blue Mountains (1000 m a.s.l.)) and two sea-level sites (Waituna 1 (0 m a.s.l.), Waituna 2 (0 m a.s.l.)) in South Island, New Zealand were used. Donatia novae-zelandiae cushions differed significantly between the high-elevation and sea-level sites both morphologically and in terms of reproduction. High-elevation cushions produced more flowers (threefold more flowers per plant) and seeds (sevenfold more seeds per capsule) than at sea level, but leaves were larger at sea level (in length and specific leaf area). The cushions were also twice as compact at the high-elevation sites. After two growing seasons of artificial warming, seed production (35%), leaf length (7%) and width (13%), and specific leaf area (63%) significantly decreased in D. novae-zelandiae plants; flower production was not significantly affected. Cushion plant morphology and reproduction were significantly affected by environmental drivers at their establishment sites, but all populations responded negatively to artificial warming of 1–3°C. Many cushion plants are considered keystone species because of their propensity to facilitate the growth and establishment of other plant species, the inferred negative effects of global warming on cushion plant species may have a cascading effect on other alpine plant groups.

Many conservation decisions rely on the assumption that multiple populations will respond similarly to management. However, few attempts have been made to evaluate indicators of population trends (i.e. population indicator species). Eradication of introduced mammals from offshore islands is a commonly used management technique for conservation of native taxa in New Zealand. Pacific rats and rabbits were eradicated from Korapuki Island in 1986/1987 enabling population recovery of native species that had been suppressed by predation or competition. However, the degree to which species’ responses were correlated has not been evaluated. We investigated correlations among lizard population trends on Korapuki Island as a test of the population indicator species concept. Our dataset consisted of captures of the five resident lizard species (three skinks, two geckos) from biannual pitfall trapping over a 10 year period (1986–1995) immediately following rodent eradication. We used a Bayesian modelling approach to examine correlations in population trends (based on mean annual counts) between species. Population trends were positively correlated for all species pairs (substantively for 90 % of pairs) and we detected no negative correlations. Systematic searches for single lizard species may indicate correlated recovery of lizard populations following rodent eradication and provide a cost-effective alternative to traditional ‘whole community’ monitoring. Our findings support evidence-based use of the population indicator species concept in cases where a shared ecological driver can be identified.

Using population indicators to evaluate conservation achievements is widely practised, yet seldom empirically tested. If populations are consistently correlated in response to a shared ecological driver, the indicator species approach can be used as a cost-effective, ecologically-based shortcut to measuring the effects of conservation management. Long-term monitoring of forest bird populations associated with mammalian pest control programmes in New Zealand provides a useful framework for testing the population indicator species concept. We evaluated population trends in 21 bird species vulnerable to predation by introduced mammals (primarily mustelids and rodents) at managed and unmanaged beech (Nothofagus) forest sites. Correlated population trends between species pairs were detected at individual sites. However, neither positive nor negative correlations in species trends could be predicted by life history traits and predator management did not produce consistent, correlated population trends among sites. Our results do not support the use of a population indicator approach to management and reporting for forest birds in New Zealand. Relationships between purported indicator taxa and other species need to be understood for various management scenarios before population indicators can be confidently applied to measuring conservation achievement.

Lost or extinct ecosystem function presents challenges for managers of natural ecosystems for conservation. One solution is to use ecological surrogates to replace these processes but the settings under which this often controversial approach succeeds are unclear. We tested whether mammalian grazing could be used as a surrogate for grazing by an extinct avian herbivore guild in two threatened coastal turf communities that are structured by an exposure and salt gradient, and vulnerable to non-native encroachment and invasion. Prostrate species had higher cover and species density relative to erect taxa when grazed, with the effect greater for native than non-native taxa. Prostrate species, dominated by native taxa, were most abundant closest to the ocean, with a secondary peak in abundance 25–35 m inland. A positive nutrient feedback mechanism consistent with a grazing lawn was not observed suggesting a primary role for the salinity gradient, augmented by opportunistic grazing of taller species, in structuring these communities. Synthesis and application: mammalian grazers can replace the likely functional role of extinct avian herbivores in turf communities under certain environmental settings.

Summary 1. Facilitation allows some plant species to occupy environments that they are otherwise unable to inhabit, potentially leading to greater fitness, greater productivity or abundance, and range expansions. However, we know little about the costs incurred by facilitators or how variation in resource allocation by facilitators influences effects and costs. 2. Gynodioecy provides an opportunity to explore the effects of facilitation and potential costs because females and hermaphrodites differ in resource allocation patterns. We explored whether environmental stress and gender-specific facilitation influence species interactions in an alpine plant community. We investigated the degree of facilitation and correlative associated costs for the gynodioecious alpine plant, Silene acaulis, at two elevations (2317 and 2560 m) in the northern Rocky Mountains of Montana, USA. 3. Hermaphroditic Silene individuals supported a greater number of plant species and individual plants than female Silene (hermaphrodites = 4.2 ± 0.3, females = 3.5 ± 0.2; hermaphrodites = 11.5 ± 1.0, females = 9.1 ± 1.1). Facilitative effects on species richness significantly increased with elevation (2.1 ± 1.6 species at the low site vs. 3.2 ± 1.8 species at the high site), but abundance and percentage cover did not. 4. Silene fitness at the high elevation site (2560 m) was reduced compared to the lower site (2317 m) as measured by flower and seed production. Female flower production decreased by 40%, the number of seeds per fruit by 11.6% and leaf size by 24%. 5. Increases in the percentage cover of beneficiaries reduced the number of flowers per Silene plant, indicating a cost of facilitating other species, and this cost was slightly greater for females. However, seed size for hermaphrodites and leaf length for females increased with the percentage cover of beneficiaries, suggesting a mutual benefit of harbouring other species. 6. Synthesis. Our results show that gender can affect the balance between competitive and facilitative interactions. Stronger facilitation by hermaphroditic Silene acaulis, coupled with a lower cost of harbouring beneficiaries, suggests that life-history traits and related patterns of resource allocation can influence the facilitative effects of a species.

Symbiotic associations between vascular plants and nitrogen-fixing bacteria are expected to be costly except when N availability is low. We tested the prediction that in low-N soils in dry climates, plants with nitrogen-fixing symbioses (N-fixing species) have higher growth rates, and occur relatively more frequently, than non-fixing species, In a pot experiment, we measured the growth and survival of 6 N-fixing and 8 non-fixing species across nitrogen and moisture gradients. Using plot survey data from the South Island, New Zealand, we then modelled the relative occurrence of N-fixing species using derived measures of temperature, soil N and moisture. Non-fixing species had higher relative growth rates than N-fixing species except when both total N and soil moisture were low. Low soil moisture increased the root:shoot ratio in N-fixing species more than twice that observed in non-fixing species. Soil moisture had a strong effect on mortality, which was slightly lower for N-fixing species. Survey data showed that a higher proportion of N-fixing species were present at cool, dry sites with low levels of soil N. In temperate climates, with geologically young landscapes, the influences of soil N and water on N availability are key factors determining the relative success of N-fixing and non-fixing species.

Plant-based defence mutualisms utilize plant morphology to reduce the performance of plant parasites through their natural enemies. Leaf domatia primarily occur in the axials of secondary veins and are often inhabited by microbivorous and predaceous mites which often increase plant growth rates and reproductive success by controlling plant pests. Our study investigated if domatia investment is limited by plant primary productivity. To our knowledge no studies have tested if foliar domatia are resource-limited. We tested our hypothesis using the genus Coprosma (Rubiaceae), conducting correlative field surveys and manipulative experiments measuring domatia production in new leaves along temperature, nutrient and irradiance gradients. Field surveys indicated a strong positive association between leaf area, the number of secondary veins, and domatia per leaf. The number of potential sites for domatia is underutilised, with leaves on selected Coprosma species having on average 47 to 72% of the 'maximum' number of available sites where domatia could occur. Foliar carbon was positively associated with domatia investment. Coprosma plants held under elevated night-time temperatures showed a 34―91 % decrease in daily carbon gain, a 38% decrease in domatia per leaf mass, and a positive relationship between domatia investment and integrated daily carbon gain. Under irradiance and nutrient stress, our data indicated evidence of a positive relationship between domatia investment and foliar carbon. We found a significant negative association between relative investment in domatia produced and investment in new leaf biomass. Our findings suggest investment in foliar domatia is limited by primary productivity. We propose that domatia are discretionary goods and not intrinsic structures produced automatically on leaves that mites utilize. We suggest that plants have the ability to regulate domatia formation during leaf ontogeny, with investment controlled by resource availability and some intrinsic allocation mechanism to defence.

This paper uses bargaining dynamics, administrative politics, and agency theory to examine financial outcomes from New Zealand land reform. Results are inconsistent with payments arising from a bargain in which both the Crown and lessee advocate to their full potential, and are instead consistent with the Crown backing down to lessees' desires for a generous deal. This back-down stems either from "bureaucratic coping," or from the addition of a bureaucratic middleman between the Crown principal and its negotiator subagent, exacerbating the principal-agent problem.

1. Habitat structure is an important factor influencing population dynamics and trophic organisation of terrestrial invertebrates. The phylloplane zone on vascular plant leaves is topographically complex, containing a multitude of microhabitats such as leaf hairs, lesions, and structural refugia such as domatia, which may modify interactions between resident invertebrate communities, colonisers, and subsequent trophic relationships. Leaf domatia are small indentations on the underside of leaves and are often inhabited by potentially beneficial mites and other arthropods. 2. This study investigated the relationship between domatia availability and foliar mite assemblages in contrasting habitats (native forest, plantation forest, and pasture) using a standard test plant (the endemic New Zealand shrub Coprosma lucida, J.R. & G. Forst.). 3. Diverse woody native vegetation types supported higher numbers of mite species than either plantation forest or pastoral grasses. The highest number of mite species occurred in the native forest (63%), plantation forest (38%), and pastoral grasses (25%). In the native vegetation type, experimental C. lucida leaves with domatia supported higher mite densities, greater colonisation success, and more diverse mite assemblages than those without domatia. Mite assemblages within the pastoral site were significantly different from the other two vegetation types. Only one fungivorous mite species, Orthotydeus californicus, occurred compared to five mite species in native and plantation forests. 4. This study indicated that foliar mite assemblages in native vegetation on experimental C. lucida shrubs are influenced by domatia availability, resident foliar mites, and local mite assemblages.

Can New Zealand’s indigenous dryland ecosystems be rehabilitated by facilitating inherent successional tendencies to enhance development of indigenous-dominated and often woody communities in the long term? Here, we describe the geographic distribution of woody communities of New Zealand’s South Island drylands to generate hypotheses about successional trajectories to future vegetation states. Presences and absences of woody species in 3880 vegetation plots collated from past surveys were used to predict species potential distributions across drylands. Separate models and spatial predictions were built for each of four classes of woody richness, which were used as surrogates for successional stages. Woody species richness increased significantly from grassland to shrubland and from shrubland to forest cover, and trends in species traits also suggest richness class was related with successional stage. Indigenous woody species outnumbered exotic species in all richness classes. Assuming richness cl...

The fitness benefits of plant structural adaptations that increase the effectiveness of fungivores against leaf pathogenic fungi are poorly understood. In a 12-month field experiment, we investigated the effect of domatia on mite density, the role of these mites in limiting leaf fungi, and the associated effects on plant fitness in the endemic New Zealand shrub, Coprosma lucida. The presence of domatia on mite density was controlled using combinations of domatia blocking, sham blocking, mite addition and mite control using miticide. Limiting access to domatia reduced mite density and increased the proportion of leaves without mites. Mite families represented were predominantly fungivorous/detritivorous (97.2%), and predaceous (2.6%); herbivorous mites were absent. Mites significantly reduced fungal hyphae, fungal spores and pollen, but the effect was surface(upper/lower) and density-dependent with the greatest reduction in fungi occurring over low mite densities. Fungal hyphae reduced leaf longevity, but were associated with increased production of new leaves. Hyphae density on old leaves was negatively correlated with the number of domatia produced on new leaves. New leaves in the mite reduction treatment had slightly reduced levels of carbon but not nitrogen. High levels of fungal infection on the lower surface increased the number of fruit fascicles per shoot, however on the upper surface where fungi were reduced by mites, hyphae density was negatively related to reproduction. The data support a limited interpretation of a fitness benefit for plants with domatia. While domatia increased mite density, control of fungi by mites occurred at lower average densities than supported by plants without functioning domatia. We suggest the primary function of leaf domatia in this mutualism is to increase the probability of a leaf-level beneficial mite presence rather than to maximise mite density. Many mites are not necessarily better than few mites, but some mites are better than none. Plant-directed defence mutualisms involving invertebrates require facilitation of the presence of beneficial

Mechanistic models can help resolve controversy over the responses of mast seeding plants to future environmental change. We evaluate drivers of mast seeding by: developing and validating a new mechanistic resource-based model of mast seeding using four 40-yr Chionochloa (snow tussock) datasets; and comparing the performance of competing empirically-based statistical models, that aim to approximate the mechanisms underlying mast seeding, in explaining simulated and observed data. Our mechanistic model explained 90-99% of the variation in Chionochloa flowering, with higher rates of stored resource mobilisation and lower probability of climatic induction of flowering occurring at lower fertility sites. Inter-annual variation in floral induction and the degree to which seeding is resource-limited explained shifts in the relative performance of different empirical models fitted to data simulated from the mechanistic model. Empirical models explicitly capturing the interaction between the floral induction cue and internal resource state underlying the resource-limited induction mechanism had > 8.7× the statistical support of alternatives when fitted to Chionochloa datasets. We find support for resource-limited floral induction with multiple empirical models consistent with this same mechanism. As both resource acquisition and flowering cues are climate sensitive, we expect climate change to impact upon patterns of mast seeding.

Leaves often decline in nutritional quality as they age, and selective feeding on young leaves may be nutritionally important for herbivores. Preference by mammalian herbivores for young leaves has rarely been measured in the field owing to technical difficulties. We measured preferences with respect to leaf age of an arboreal folivore, the brushtail possum ( Trichosurus vulpecula Kerr), feeding on southern rata ( Metrosideros umbellata Cav.; Myrtaceae) in a new application of the alkane technique. We characterized the cuticle waxes (n-alkanes) of rata leaves that were less than 1 year old ('1-year'), between 1 and 2 years ('2-year') and greater than 2 years old (' > 2- year'). Simulations showed that the method accurately discriminated between 1-year and other age groups but slightly overestimated the importance of rare components of the diet. This bias was larger when discriminating between 2-year and > 2-year leaves apparently because they had more-similar alkane profiles. Metrosideros umbellata leaf formed 20.8% of the diet of a population of possums from Rakiura, New Zealand, sampled in autumn 2002 ( n = 33). Of the M. umbellata component, alkane analyses showed that 1-year leaves formed 88.7 ± 3.9% of the diet despite making up only 39.5 ± 2.2% of the leaf biomass on rata trees ( n = 14). The foliar concentrations of the macronutrients N, P and K all declined significantly with leaf age ( P < 0.0001). Lignin content did not measurably increase with leaf age, suggesting that digestibility per se did not determine the preference of brushtail possums for young rata leaves. This study provides the first quantitative evidence that possums discriminate by leaf age and that the resulting diet is enriched in macronutrients.

The genus Nothofagus in New Zealand and Australia exhibits strong mast seeding (i.e. highly variable seed crops between years). Seed crop variation is synchronized within and between species over large spatial scales, and results in greatly increased wind pollination efficiency which could provide a selective benefit favouring the maintenance of mast seeding. However, the null hypothesis (that plants simply match their reproductive effort to the variable resources available each year) has not been tested in Nothofagus. Here we use a 33-year dataset on seedfall and wood ring increments for 19 individual Nothofagus truncata trees at Orongorongo, New Zealand, to test for the presence of switching (exaggeration of seedfall variability by diverting resources into, then out of, reproduction). A generalized least squares model explained 40.7% of the variance in standardized ring widths, using six weather variables (absolute minimum temperatures in March (lag 0) April (lag 0 and lag 1), May (lag 0) and rainfall in November and February (lag 0) ) and seedfall. Seedfall had a negative relationship with the current year's ring widths even after controlling for all significant weather variables. This shows that switching is occurring in N. truncata within individuals among years, and therefore that masting in this species is the result of selective forces such as increased wind pollination efficiency. As this result has been demonstrated for very few masting species, we call for this test to be applied more widely.

It is widely accepted that previous experience and internal physiological factors (such as egg-load) affect host-plant discrimination during oviposition by phytophagous insects. However, there is some debate as to how these factors interact in a mechanistic sense to control acceptance. The role of learning and host deprivation in host acceptance by adult diamondback moths (Plutella xylostella L.) was investigated. In the first experiment, we tested whether experience of a lower ranked host cabbage increased acceptance of a higher ranked host as predicted by a hierarchy threshold model. Moths trained on cabbage were over three times more likely to accept cabbage during testing than untrained moths. There was no effect of cabbage training on acceptance of cress, indicating that the effect of training was species-specific. In a second experiment, designed to test the prediction of motivation models that insects become less discriminating when deprived of oviposition opportunities, depriving females of host plants for 2 nights significantly increased female egg-load (×2.3). Host deprivation did not decrease discrimination between the preferred host cress and cabbage. Cabbage and cress plants were equally likely to have been accepted by nondeprived moths after 1 night of exposure, yet moths deprived of hosts for 2 nights strongly preferred cress when tested during the first 20 min of the scotophase. During this 20-min period, previous host deprivation increased acceptance of host plants generally but did not decrease discrimination between hosts. These data contradict the expectation that there is an inverse relationship between host species discrimination and the failure of an insect to find hosts as found in existing oviposition acceptance models. As an alternative, the Incremental Acceptance Model of host acceptance behaviour is presented, in which responsiveness to a host is a function of the recent encounter rate with host-specific stimuli, and the oviposition reflex is regulated by nonspecific cues such as egg-load.

Ecological processes often maintain the plant communities with which they have a long evolutionary association, and so their loss may favor invasions by nonnative species. We simulated the effects of fecal deposition and soil turnover by the extinct avian megafauna of New Zealand to test their influence on woody plant regeneration and nonnative plant invasion in a cool temperate rain forest. Hen manure increased soil available NO3-, leading to greater seedling regeneration relative to control plots. Although soil P was elevated within plots treated with hen manure, concentrations also increased within plots treated with liquid fertilizer, which did not have different seedling densities relative to controls. Simulated avian soil disturbance did not increase seedling densities, and none of the three treatments affected the proportion of woody seedlings that were nonnative. However, pretreatment variation in NO3- availability, which reflected longer-term rates of nitrogen cycling, reduced community invasibility. Our findings suggest that avian-derived nitrogen inputs increase the regeneration of native forests, raising the question of whether the functional role of extinct megaherbivores is absent in New Zealand.

Context Low-volume control agents based on new biotechnologies are likely to be point-delivered to wildlife populations using devices such as bait stations. However, data and theory to underpin the development of strategies for such a use of bait stations are lacking. Aims In a large-scale replicated field trial of brushtail possum (Trichosurus vulpecula) populations, we estimated the levels of coverage achieved with bait-station grids at three densities (0.2, 0.6 and 1.0 ha–1), with and without pre-feeding, to test the predictions of an existing model of bait-station delivery based on relationships derived from leghold trapping. Methods We first marked possums using conventional capture–mark–recapture techniques, and then estimated population coverage by recovering animals poisoned by encapsulated cyanide delivered by the bait stations. Key results The two key model predictions, that 90% population coverage could be achieved at 0.6 bait stations per hectare and that pre-feeding was not required to achieve this level, were not upheld by the field trials. Instead, there was a poor fit between model predictions and observed levels of population coverage. An investigation of key model assumptions demonstrated issues with both model structure and parameterisation. Conclusions Neither previously documented relationships for possum interactions with leghold traps, nor correlations between possum interaction rates with such devices and bait stations, are generically applicable across all populations. Implications While the existing model of bait-station delivery to possums fits the data for some field operations and trials, it is not applicable to all populations. Incorporating habitat and seasonal effects on possum home-range behaviour could potentially improve model prediction. Our results also have implications for the accuracy of index-based methods of possum population monitoring that use leghold traps, such as the Residual Trap Catch Index.

Context Many conservation decisions rely on the assumption that multiple populations will respond similarly to management. However, few attempts have been made to evaluate correlated population responses to management or to identify traits that could be used to predict correlations. These assumptions are central to the use of the ‘population indicator-species concept’ (the idea that population trends of one species can be used as an index of trends in other species) for measuring the effects of key ecological drivers. Aims We investigated correlations among bird population trends in a mixed podocarp–hardwood forest in New Zealand in which introduced mammalian pests are controlled. We analysed trends in the abundance of 18 bird species (primarily passerines) over a 10-year period, using data from 5-min bird counts. Methods We used a Bayesian modelling approach to identify short-term correlations in population trends among species and to investigate whether ecological traits can be used to predict these correlated trends. Key results Population increases were detected in 9 of the 18 bird species over the 10-year period of the study. Population trends were correlated for 10% of species pairs (of which 81% were positive correlations). Correlations among seven of the nine species that increased in abundance were always positive; these species form a potential indicator pool. However, traits were not useful for predicting correlated population trends. Conclusions Bird species affected by a shared ecological driver (predation) can exhibit correlated population trends when introduced predators are controlled, but correlations cannot be predicted by similarity in ecological traits. Implications We advocate for testing consistency of correlations at multiple sites so as to validate the evidence-based use of the population indicator-species concept as a cost-effective alternative to monitoring whole communities.

Few validated studies have tested the n-alkane method for diet estimation in non-ruminants and the technique has rarely been validated for estimating diet composition for more than two dietary components. The arboreal marsupial Trichosurus vulpecula was fed leaf and fruit diets with up to five component species in two trials. In Trial 1, alkane recovery was estimated, and in Trial 2 these estimates were used to predict digestibility, diet composition and dry matter intake. Alkane recovery increased non-linearly (convex up) with increasing n-alkane chain length. Recovery was linearly and negatively correlated with diet digestibility and appeared to explain a progressive bias with observed digestibility in the alkane estimates of digestibility (slope = 0.37). Diet composition was successfully estimated for up to five leaf dietary components without correction for recovery. Correcting for recovery gave less reliable diet-composition predictions, indicating that the recovery estimates could not be extrapolated to the second trial. Dry matter intake appeared to be relatively robust to variation in alkane recovery between individuals (mean bias =1.6%). If recovery is shown to vary with digestibility in other taxa, calibration of the alkane technique will require diet- and taxon-specific calibration trials to give reliable estimates of diet composition and dry matter digestibility.