Metapopulation persistence depends on connectivity between habitat patches. While emphasis has been placed on the spatial dynamics of connectivity, much less has been placed on its short‐term temporal dynamics. In many terrestrial and aquatic ecosystems, however, transient (short‐term) changes in connectivity occur as habitat patches are connected and disconnected due, for example, to climatic or hydrological variability. We evaluated the implications of transient connectivity using a network‐based metapopulation model and a series of scenarios representing temporal changes in connectivity. The transient loss of connectivity can influence metapopulation persistence, and more strongly autocorrelated temporal dynamics affect metapopulation persistence more severely. Given that many ecosystems experience short‐term and temporary loss of habitat connectivity, it is important that these dynamics are adequately represented in metapopulation models; failing to do so may yield overly optimistic‐estimates of metapopulation persistence in fragmented landscapes.

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The dietary breadth of invaders can influence their success, and having a wide dietary niche can facilitate the spread and survival of invaders under a variety of resource scenarios. The western mosquitofish (Gambusia affinis) is a globally distributed freshwater invasive fish. The spread of G. affinis is associated with agricultural land use, although the trophic role it plays in degraded systems is not well understood. We analysed the invertebrate community in 11 stream reaches in the North Island of New Zealand, in catchments spanning a range (45%-90%) of agricultural land use to determine how prey availability changes with land use. We then analysed the gut contents of 400 G. affinis from the 11 sites to determine how diet varied with prey availability and ontogeny. Invertebrate communities varied along the agricultural land-use gradient, both in regard to taxonomic richness and community composition.G. affinis consumed a wide variety of food items with invertebrates being the most dominant, in particular Culicidae, Copepods and amphipods were the most commonly consumed invertebrates. There was also an ontogenetic diet shift from microinvertebrates (Cladocera, Copepods and diatoms) to larger invertebrates, including Culicidae, amphipods and terrestrial invertebrates. G. affinis are capable of consuming a wide variety of prey in agricultural streams; their preferred prey are generally pollution-tolerant taxa commonly found in degraded streams. Having a large level of dietary plasticity coupled with preferring prey that are often associated with degraded systems likely facilitates to the spread of one of the most widely distributed freshwater invasive fish. K E Y W O R D Sagriculture, diet plasticity, Gambusia affinis, invasive species | 823 LEE Et aL.

Some extinctions have obvious drivers (e.g. over‐harvesting), while others can be less obvious and arise from multiple interacting factors. The extinction of the New Zealand grayling (Prototroctes oxyrhynchus) has been blamed on over‐fishing and predation by introduced trout, but these explanations fail to account for the species disappearance from isolated, uninvaded rivers. We investigated if source–sink dynamics, facilitated by P. oxyrhynchus's amphidromous dispersal habit, could account for the species’ rapid extinction. We created a database of P. oxyrhynchus sightings by surveying newspapers dating back to 1839, along with a review of traditional scientific literature. We used this database to update P. oxyrhynchus's known distribution map and inform sighting models to predict P. oxyrhynchus's extinction date. Finally, we implemented a meta‐population model to explore how source–sink dynamics could interact with off‐take (over‐fishing or predation) to drive extinction. Prototroctes oxyrhynchus was found across New Zealand, except the north of the North Island. Based on sightings methods, the earliest predicted extinction date was 1924, although the species may have persisted until 1972, later than previous estimates have suggested. In the absence of source–sink dynamics, relatively high levels of off‐take were sustainable (up to 30% per generation). When the species was modelled as a panmictic meta‐population including 5% sink habitats, the sustainable off‐take rate was reduced to as low as 5% per generation. Prototroctes oxyrhynchus was a widespread, abundant species that underwent rapid declines and ultimately went extinct. Previous attempts to explain this extinction have failed to account for the species extinction from isolated, pristine rivers. Our modelling shows that treating the species as a panmictic metapopulation and including source–sink dynamics rapidly increases the probability of extinction. We suggest that source–sink dynamics may be an important aspect of the population dynamics of amphidromous species and should be considered when managing taxa with similar dispersal habits.

Biodiversity assets often require conservation management, which, in turn, necessitates decisions about which ecosystem, community or species should be prioritised to receive resources. Population viability analysis (PVA) uses a suite of quantitative methods to estimate the likelihood of population decline and extinction for a given species, and can be used to assess a population's status, providing useful information to decision-makers. In New Zealand, a range of taxa have been analysed using the PVA approach, but the scope of its implementation has not previously been reviewed. We compiled a database of 78 published PVAs for New Zealand indigenous fauna and flora, along with details of the species considered, the data used to parametrise the model, and the technical details of their implementation. We assessed the taxa and threat status of the species for which PVA were conducted relative to the distribution of taxa across threat classes in the New Zealand Threat Classification System database. There were clear biases in the species selected for analysis, notably an over-representation of birds and threatened species in general, and an under-representation of invertebrates and plants. Model parameterisation and implementation were often not reported in a transparent or standardised way, which hinders model communication and reconstruction. To maximise the benefit of PVAs, we suggest that more attention should be given to the ecosystem-level importance of species, and to species whose threat status is changing rapidly or are not yet threatened. More clearly describing the parameterisation, underlying assumptions and implementation of PVAs will help to better contextualise their results and support reproducible ecological science and decision-making.

1. River networks are frequently simulated for use in the development and testing of ecological theory. Currently, two main algorithms are used, stochastic branching networks (SBNs) and optimal channel networks (OCNs). The topology of these simulated networks and 'real' rivers is often quantified using graph theoretic metrics; however, to date, there has not been a comprehensive analysis of how these algorithms compare regarding graph theoretic metrics, or an analysis of metric redundancy and variability across dendritic ecological networks. We aim to provide guidance as to which algorithm and metrics should be used, and under what circumstances.2. We performed an extensive simulation study in which we (a) identified orthogonal sets of metrics that describe the topology of real and simulated river networks, (b) analysed the relationship between algorithm hyper-parameters and node topology metrics, (c) determined whether simulated and real rivers are indistinguishable in their graph metric scores and (d) examined how patterns of species abundances compare across the three network types.3. We identified two orthogonal sets of node metrics; those that describe centrality and those that describe neighbourhood characteristics. Both stochastic branching networks and optimal channel networks can reproduce network topology metric scores of real rivers, but this relationship is dependent on the algorithm hyper-parameters used. Finally, using a metapopulation model, we show that both SBNs and OCNs can reproduce ecological patterns of species abundances similar to those of real rivers.4. SBNs and OCNs can replicate the node topology of real rivers. The choice of which algorithm to use will depend on the research aims, SBNs are faster to generate and more tractable, whereas OCNs can reproduce a wider variety of the characteristics of real rivers, but are more time-consuming to generate. When quantifying node topology in river networks, we recommend the orthogonal node metrics eccentricity, when interested in network centrality, and mean neighbour degree, when interested in local node importance.

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Changes in connectivity regimes affect patterns of diversity and species richness. In riverine ecosystems, factors that vary through space and time, such as flow, the presence of barriers to movement, and network topology determine connectivity, and in turn shape patterns of diversity and richness.While the effects of network topology and changes in spatiotemporal connectivity regimes on patterns of species richness have been studied in isolation, they have not been studied simultaneously. We used a discrete-time logistic growth metacommunity model to analyze the role of spatial and temporal functional connectivity in determining patterns of local (patch level) species richness in freshwater fish metacommunities. Our modeling suggests that:(1) the effect of spatial loss of connectivity on local species richness is mediated by network topology and where richness is measured in the system and (2) increasing temporal autocorrelation in connectivity results in increasing temporal autocorrelation in patch occupancy. Spatial and temporal loss of connectivity is a ubiquitous issue for river ecosystems, making understanding and predicting its effects of fundamental importance to both improving theory and guiding river management. Our findings highlight the importance of network topology (and hence context dependency) in shaping metacommunity response to changing connectivity regimes.