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Spatial classifications of the environment have previously been used to characterise biodiversity and to facilitate management planning at large spatial scales. Such classifications are more likely to be adopted if they can demonstrate integration of real patterns in habitats or biotic assemblages, in addition to environment. A previous classification used Gradient Forest analysis to derive 30 classes based on demersal fish assemblage patterns and environmental gradients. Here we provide a detailed description of the similarities and differences in the environment and fish assemblages of classes resulting from an updated classification using the same methodology. Environmental differences were associated with varying levels of differences in the distributions of fish species. At broad spatial scales, assemblages are differentiated primarily according to oceanographic conditions such as temperature and depth; at finer scales, patterns in species assemblages are more closely associated with more localised environmental conditions such as productivity, sea-surface temperature gradients and tidal currents. The 30-group classification allows complex biodiversity information to be summarised in ways accessible to stakeholder and environmental managers. Given the hierarchical nature of the classification, there is considerable scope to use a larger number of groups for applications at regional to local scales.

Predictions of invasion risk for seven non-indigenous fish species, ecological impact scores for individual species, and lake conservation rankings were linked to develop Invasion Risk Impact (IRI) and Lake Vulnerability (LV) indices that help identify New Zealand lakes most at risk of loss of conservation value from potential multi-species invasions. Species-specific IRI scores (the product of predicted invasion risk and species impact) highlighted Eurasian perch (Perca fluviatilis) and the brown bullhead (Ameiurus nebulosus), as the species most likely to spread and cause ecological harm in lakes. For 3431 lakes >1 ha throughout New Zealand, total IRI tended to be highest for lowland riverine and dune lakes most of which are already colonized by multiple invasive fish species. The LV index indicated that lakes most at risk of loss of conservation value from invasive fish impacts were predominantly (i) in the northern half of the North Island where several uncommon lake types occur, and (ii) along the west coast of the South Island where conservation value is often greater, largely because of low catchment modification. The IRI and LV indices can be used to assist with setting priorities for surveillance monitoring, advocacy, and response planning targeted at preventing the establishment of invasive fish in moderate-to-high value lakes most susceptible to ecological impacts. Both indices can be adapted to accommodate alternative impact and conservation scoring systems, providing a flexible tool for local- and national-scale assessments of lake vulnerability to fish invasion impacts. Copyright © 2016 John Wiley & Sons, Ltd.

We applied a multivariate statistical modelling technique called boosted regression trees to derive relationships between environmental conditions and the distribution of the adult stage of the cyclopoid copepod Oithona similis in the Southern Ocean. Nearly 20 000 samples from the Southern Ocean Continuous Plankton Recorder survey (87% from East Antarctica) were used to model the probability of detection (presence) and relative abundance of adults of this zooplankton species in surface waters. We demonstrate that it is possible to obtain reasonable models for both the presence (area under the Receiver Operating Characteristic curve of 0.77) and relative abundance (28–35% variance explained) of adult O. similis between November and March in much of the Southern Ocean. No investigation was possible where the environmental characteristics were not well represented by the SO-CPR dataset, namely, the Argentine shelf, Weddell Sea, and the frontal region north of the Amundsen Sea, or under sea-ice. Our analyses support the hypothesis that adult O. similis abundance is related to environmental conditions in a broadly similar way throughout the Southern Ocean. Compared to a compilation of net-haul data from the literature, the abundance model explained 34% of the variance in surface concentrations of adult stages of this species, and 23–59% of the variance in depth-integrated abundance of copepodite and adult stages combined. The models show higher occurrence and elevated abundances in a broad circumpolar band between the Antarctic Polar Front and the southern boundary of the Antarctic Circumpolar Current (approximately 54–64°S). Evidence of diel vertical migration by adults of this species north of 65°S was found, with surface abundances 20% higher at night than during the day. There was no evidence of diel migration south of 65°S. Five potential “hotspots” of adult O. similis were identified: in the southern Scotia Sea, two areas off east Antarctica, in the frontal zone north of the Amundsen Sea, and a small area in the outer Bellingshausen Sea. We recommend that a database of all available net-haul data on Oithona similis in the Southern Ocean be created to facilitate further investigations on the circumpolar distribution of this species.

Aim The highly adaptable estuarine crab (Carcinus maenas) has successfully invaded five temperate geographic regions outside of its native Europe. Here, we determine which environmental factors predict the current distribution of C. maenas and what the potential geographic range of this species might be. We also investigated whether the invasion potential of C. maenas differs with respect to the origin of a native subpopulation. Location Models were developed using global observation records of C. maenas. Methods Boosted regression trees were used to model observations from the (1) native, (2) invasive, (3) southern European, (4) northern European and (5) the combined native and invasive geographic ranges of C. maenas. Results Most established invasions were predicted mainly based on temperature. Interestingly, the environment encountered by established invasions failed to predict the majority of northern European populations; suggesting that invasion potential may differ between distinct native populations. Supporting this suggestion, a model of northern European populations, distinguished from southern European populations based on genetic structure, only predicted established invasions south of Nova Scotia. By contrast, a model of southern European populations predicted most established invasions. Main conclusions These results suggest that invasion potential depends on the European origin of an invasive population and that most invasions have arisen from southern Europe. Finally, a model based on combined native and invasive ranges of C. maenas identified potential geographic range extension along many currently invaded coastlines and the potential invasion of countries like Chile, China, Russia, Namibia and New Zealand.

We used statistical models to predict the distributions of 15 native diadromous fish species across New Zealand's river and stream network, and demonstrate their potential use for guiding the restoration of freshwater ecosystems. Models were fitted to an extensive collection of field samples describing the distributions of individual fish species, coupled with a set of environmental predictors chosen primarily for their functional relevance to diadromous fish species. Models were fitted to observations of species occurrence using boosted regression trees (BRT), an advanced regression technique that combines excellent predictive performance with good description of relationships between species occurrence and individual environmental predictors. Environment‐based predictions of species distributions were then made for all river and stream segments. We explored the use of these predictions to guide the selection of sites where diadromous species are likely to occur, and to set restoration targets, ...

Aim To examine the relationship between diadromy and dispersal ability in New Zealand’s freshwater fish fauna, and how this affects the current environmental and geographic distributions of both diadromous and non-diadromous species. Location New Zealand. Methods Capture data for 15 diadromous and 15 non-diadromous fish species from 13,369 sites throughout New Zealand were analysed to establish features of their geographic ranges. Statistical models were used to determine the main environmental correlates of species’ distributions, and to establish the environmental conditions preferred by each species. Environmental predictors, chosen for their functional relevance, were derived from an extensive GIS database describing New Zealand’s river and stream network. Results In terms of geography, most diadromous species occur in a scattered fashion throughout extensive geographic ranges, and occupy large numbers of catchments of widely varying size. By contrast, most non-diadromous species show relatively high levels of occupancy of smaller geographic ranges, and most are restricted to a few large catchments, particularly in the eastern South Island. In terms of environment, there is marked separation of diadromous from non-diadromous species, with diadromous species generally caught most frequently in low-gradient coastal rivers and streams with warm, maritime climates. With a few notable exceptions, most diadromous species have lower occurrence in river segments that are located above obstacles to upstream migration. Non-diadromous species are usually caught in inland rivers and streams with cool, strongly seasonal climates, typified by a low frequency of high-intensity rainfall events. Main conclusions We interpret the contrasting biogeographies of New Zealand’s diadromous and non-diadromous species as reflecting interaction between their marked differences in dispersal ability and a landscape that is subject to recurrent, often large-scale, natural disturbance. While both groups are likely to be equally susceptible to local, disturbance-driven extinction, the much greater dispersal ability of diadromous species has allowed them to persist over wide geographic ranges. By contrast, the distributions of most non-diadromous species are concentrated in a few large catchments, mostly in regions where less intense natural disturbance regimes are likely to have favoured their survival.

There is strong international agreement on the need for marine protected areas to reverse pervasive human impacts on the oceans’ biodiversity. However, their implementation is often hampered both by legal difficulties in defining reserves in international waters and the patchy nature of data in many offshore waters. We demonstrate the use of recent advances in statistical learning and conservation prioritization to produce MPA scenarios with varying costs and benefits for New Zealand’s Exclusive Economic Zone, based on the analyses of distributions of 96 demersal fish species. MPAs based on our most costeffective scenario would deliver conservation benefits nearly 2.5 times greater than those from equivalent-sized areas recently implemented at the request of fishers, and at lower cost to them. Such results demonstrate the power of quantitative, knowledge-based prioritization approaches, which can be applied at high resolution and at oceanic scales.

We analysed relationships between demersal fish species richness, environment and trawl characteristics using an extensive collection of trawl data from the oceans around New Zealand. Analyses were carried out using both generalised additive models and boosted regression trees (sometimes referred to as 'stochastic gradient boosting'). Depth was the single most important envi- ronmental predictor of variation in species richness, with highest richness occurring at depths of 900 to 1000 m, and with a broad plateau of moderately high richness between 400 and 1100 m. Richness was higher both in waters with high surface concentrations of chlorophyll a and in zones of mixing of water bodies of contrasting origins. Local variation in temperature was also important, with lower richness occurring in waters that were cooler than expected given their depth. Variables describing trawl length, trawl speed, and cod-end mesh size made a substantial contribution to analysis out- comes, even though functions fitted for trawl distance and cod-end mesh size were constrained to reflect the known performance of trawl gear. Species richness declined with increasing cod-end mesh size and increasing trawl speed, but increased with increasing trawl distance, reaching a plateau once trawl distances exceed about 3 nautical miles. Boosted regression trees provided a powerful analysis tool, giving substantially superior predictive performance to generalized additive models, despite the fitting of interaction terms in the latter.

Competitive interactions between New Zealand's four Nothofagus or southern beech species were analysed using an extensive dataset describing the composition of natural forests, supplemented by environmental estimates describing both climate and landform. Using multiple regression models of progressively increasing complexity, the analysis first accounted for variation in tree abundance attributable to both environment and regional-scale distributional disjunctions of likely historic origin. Intra-generic competition, expressed as variation in tree abundance dependent on the presence or absence of each congener, was then assessed by adding (1) simple terms to assess the magnitude of gross changes in abundance, and (2) interaction terms to assess variation in abundance along the dominant temperature gradient given different competitive contexts. Results indicate the presence of substantial intra-generic interactions, with simple interaction terms giving marginal increases in explained deviance equal to that explained by initial regressions using environment alone. Addition of interaction terms brought about smaller improvements in model fit, but confirm that variation in abundance along the dominant annual temperature gradient is strongly influenced by the competitive context provided by the remaining congeners. Such results are consistent with current understanding of the niche concept, and underline the difficulty inherent in using current species limits to predict likely changes in species distributions consequent on global warming.

New Zealand's four broad-leaved evergreen tree species from the genus Nothofagus all show pronounced distributional disjunctions, independent of environmental factors known to influence tree distributions. Here, we use these disjunctions as the basis for a natural removal experiment to investigate competitive interactions between Nothofagus and a range of other widespread conifer and broad-leaved tree species. We first model the abundance of non-Nothofagus species as a function of environment, using Generalized Additive Models (GAMs) and an extensive data set sampling much of New Zealand's remaining old-growth forests. We then assess the effects of competitive interaction with Nothofagus by adding statistical terms describing (1) Nothofagus abundance, and (2) interactions between Nothofagus abundance and annual temperature, the dominant environmental gradient. Results indicate substantial reductions in the abundance of many species as Nothofagus abundance increases. The magnitude of this reduction varies with position along the dominant environmental gradient; species overlapping most strongly with Nothofagus are generally most sensitive to increases in Nothofagus abundance. In addition, both the shapes of species responses to mean annual temperature and the positions of their optima change as Nothofagus abundance increases. This demonstration of competition using community compositional data has implications both for vegetation theory and for prediction of the likely impacts of global warming on New Zealand's forest pattern.

Correlations between environment and tree alpha-diversity in New Zealand's primary forests were examined using an extensive quantitative dataset (14 540 plots). Generalised additive models were used to examine relationships between species richness and temperature, solar radiation, root-zone moisture deficit, relative humidity, lithology, drainage, and plot size for all trees (112 species), and separately for broadleaved trees (88 species), conifers (17), and the genus Nothofagus (4). Diversity both for all tree species and for broadleaved trees was predicted to be highest on sites with high temperatures, high solar radiation, and high soil and atmospheric moisture, and on sedimentary and basaltic substrates. Highest conifer diversity was predicted on sites with intermediate temperatures, low solar radiation, high root-zone and atmospheric moisture. and rhyolitic and Quaternary substrates, particularly where drainage was impeded. Highest Nothofagus diversity, was predicted for sites combining low temperatures, high solar radiation. high root-zone moisture but low atmospheric moisture, and on granitic substrates. Differences in diversity between the species groups on different lithologies are interpreted as reflecting both the effects of variation in large-scale disturbance histories, and the effects of confounding environmental factors associated with particular substrates. There were also significant interactions between species groups: both broadleaved tree and conifer richness were predicted to be lower on sites where one or more Nothofagus spp. - all of which have marked patchiness in their distribution - are present. Although these results are consistent with the hypothesis that tree diversity is highest on sites conducive to high productivity, history is also indicated as an important determinant of tree diversity in New Zealand.

Past explanations of the large disjunctions in the distribution of New Zealand's four Nothofagus species have emphasized displacement during glacial cycles followed by slow re-occupation of suitable sites, or the effects of plate tectonics coupled with ecological and/or environmental limitations to further spread. In this study the degree of equilibrium between Nothofagus distribution and environment was compared with that of other widespread tree species by statistical analysis. Generalized additive regression models were used to relate species distribution data to estimates of temperature, solar radiation, soil water deficit, atmospheric humidity, lithology and drainage. For each species, the amount of spatial patterning remaining unexplained by environment was assessed by adding a variable describing species presence/absence on adjacent plots. Results indicate that Nothofagus species occur more frequently in environments suboptimal for tree growth, i.e. having various combinations of cool temperatures, low winter solar radiation, high root-zone water deficit, low humidity, and infertile granitic substrates. Despite these demonstrated preferences, they exhibit substantially more spatial clustering which is unexplained by environment, than most other widespread tree species. Predictions formed from regressions using environment alone confirm that several major Nothofagus disjunctions are not explicable in terms of the environmental factors used in this analysis, but more likely reflect the effects of historic displacement coupled with slowness to invade forest dominated by more rapidly dispersing endomycorrhizal species. The technique used in this study for detecting residual spatial autocorrelation after fitting explanatory variables has potentially wide application in other studies where either regression or ordination techniques are used for analysis of compositional data.

The introduced brushtail possum Trichosurus vulpecula Kerr is recognised as the primary agent of defoliation and stand-level dieback in New Zealand broadleaved forests (except Nothofagus). The distribution and magnitude of canopy collapse of forest in 33 500 ha of the southern Ruahine Range, New Zealand was mapped from 1995 polychrome aerial photographs. Relationships between canopy collapse and forest type, altitude, aspect and slope were analysed using generalised additive models. Canopy composition was the strongest factor predicting the extent of collapse and modification: broadleaved-conifer forest is most affected, with 68–87% of the area of six such forest types replaced by scrub-low forest and tree-fernland; and surprisingly, three Nothofagus-dominated types have up to 28% of their former area now in shrubland or tussock grassland. The susceptibility to collapse of Nothofagus forest was positively correlated with distance to non-Nothofagus forest types. Subalpine scrub, which is dominated by species not favoured by possums, has increased in area by 32%, replacing former upper montane forest. Physiographic factors were much less important in multiple regressions. However, in general terms, forests on steeper slopes, in the upper montane-subalpine zone, and on warm westerly and northerly aspects were more susceptible to collapse and modification than elsewhere. It is postulated that possums were the primary agent responsible for collapse of non-Nothofagus broadleaved forest, and that red deer Cervus elaphus and goats Capra hircus were responsible for inhibiting canopy replacement by eliminating regeneration in forest understoreys. Secondary effects, such as outbreaks of defoliating insects and mechanical damage from wind also contributed to canopy collapse and were possibly triggered by possums opening up the canopy. Collapse of Nothofagus canopies possibly results from a breakdown in the recruitment phase of stand turnover, by the smothering effects of deer-induced shrubs and tussock grasses on seedlings and saplings.

A dataset of some 10 000 plots was used to describe the climatic relationships of 33 widespread New Zealand tree species. Estimates of mean annual temperature, temperature seasonality, mean annual solar radiation, and moisture balance were derived from mathematical surfaces fitted to climate station data. Plots were also categorized into five lithological classes and three drainage classes. Generalized additive models were used to examine species/environment relationships. Mean annual temperature and mean annual solar radiation are most strongly correlated with current tree distributions, followed by moisture balance, temperature seasonality, lithology, and drainage. Most broad-leaved tree species other than Nothofagus spp. reach their greatest levels of occurrence in warm, moist environments with high solar radiation. In contrast, Nothofagus spp. generally reach their greatest levels of occurrence in cooler and/or lower insolation environments, and all have lower levels of occurrence on rhyolitic substrates which have resulted from large-scale geomorphic disturbance, mostly over the past few thousand years. Although coniferous species have widely differing climatic optima, many are biased towards lithological classes characterized either by large-scale geomorphic disturbance or harsh edaphic conditions. The relevance of these results to particular synecological questions is briefly discussed. Continuing adjustments in the range of slow-dispersing Nothofagus spp. are strongly suggested, and the climatic suitability of extensive rhyolitic basins in the central North Island, from which these species are largely absent, is confirmed.

Nine native diadrornous and 2 exotic fish species were recorded in an intensive survey of tributaries of the Mokau River. At the site level, species diversity was low and much of the fauna had a very restricted distribution. Sites were grouped on the basis of their species composition using the classification procedure 2‐way indicator species analysis. Four groups of sites were identified, characterised by: (1) a longfinned eel‐elver assemblage; (2) a longfinned eel‐adult redfinned bully assemblage; (3) an inanga‐adult redfinned bully assemblage; and (4) a torrentfish‐bluegilled bully‐redfinned bully‐elver assemblage. Relationships between fish assemblage distribution patterns and environmental factors were examined with multiple discriminant analysis. The overriding feature influencing patterns of fish distribution was the prevalence of diadromy in the fauna with species varying in their ability to penetrate upstream. Distance from the sea and gradient from the river mouth were the environmental...