Angus R. McIntosh

University of Canterbury | UC · School of Biological Sciences

The lack of data from non-perennial rivers, which regularly cease to flow and dry up, poses a significant challenge in understanding river biodiversity. These dynamic ecosystems, accounting for over half of the global river network, remain understudied. To address this gap, we conducted a coordinated experiment and a metabarcoding approach on envir...

Ecological disturbances act as environmental filters by removing species with particular characteristics, resulting in community types associated with different disturbance histories. However, studies to date on community responses to disturbance have neglected the potential for different community assemblages to display different responses. Using...

Freshwater ecosystems worldwide are under increasing pressure from multiple threats, including invasive species and climate change, with ponds being particularly vulnerable because of their shallow depth and dynamic hydrology. Australian brown tree frogs Litoria ewingii , introduced to New Zealand in 1875, have spread across both main islands, bree...

Amphidromy is a distinctive life‐history strategy of some fish species that involves spawning in fresh or brackish water followed by dispersal to sea by newly hatched larvae, where they develop for a short period. Individuals then return to freshwater as juveniles, where they feed and grow, before maturing and spawning. Six amphidromous species fro...

With the global decline of freshwater fishes, quantifying the body size-specific habitat use of vulnerable species is crucial for accurately evaluating population health, identifying the effects of anthropogenic stressors, and directing effective habitat restoration. Populations of New Zealand's endemic kōkopu species (Galaxias fasciatus, G. argent...

In ecology and evolution, the small population paradigm posits that reduced genetic variation will result in limited phenotypic variation that, in turn, will affect population resilience and potential for adaptation. Over the last decade though, such a paradigm has been questioned, with evidence that mechanisms independent of genetic variation may...

Habitat modification and introduced mammalian predators are linked to global species extinctions and declines, but their relative influences can be uncertain, often making conservation management difficult. Using landscape-scale models, we quantified the relative impacts of habitat modification and mammalian predation on the range contraction of a...

Scientific support invited by Indigenous peoples and local communities (IPLC) to assist with customary environmental management can improve conservation and community livelihoods. For example, demographic models can help to understand how alternative wildlife management strategies affect population dynamics and harvest sustainability. We developed...

The generalizable functional attributes of organisms (traits) relate strongly to their environment across multiple levels of biological organization, making trait‐based approaches a powerful mechanistic framework to understand species distributions and community composition in relation to environmental change. To investigate how a wide range of str...

Trophic cascades are important features of aquatic ecosystems, but much variation in their strength remains unexplained. Disturbance could restrict cascade occurrence by limiting predator distribution, and increase cascade strength by lowering defended herbivore abundance. These possibilities were investigated in 20 New Zealand rivers varying both...

In organisms with complex life cycles, the various stages occupy different habitats creating demographically open populations. The dynamics of these populations will depend on the occurrence and timing of stochastic influences relative to demographic density dependence, but understanding of these fundamentals, especially in the face of climate warm...

With the global decline of freshwater fishes, quantifying the body size-specific habitat use of vulnerable species is crucial for accurately evaluating population health, identifying the effects of anthropogenic stressors, and directing effective habitat restoration. Populations of New Zealand’s endemic kōkopu species ( Galaxias fasciatus , G. arge...

Riparian plants provide an important source of energy for freshwater food webs through inputs of leaf litter. Planting riparian buffers with mixed species could enhance the detrital resource supply for invertebrates through varied leaf breakdown rates. To quantify leaf breakdown rates and invertebrate colonisation, we used leaves from eleven grass,...

Mechanisms linked to demographic, biogeographic and food-web processes thought to underpin community stability could be affected by habitat size, but the effects of habitat size on community stability remain relatively unknown. We investigated whether those habitat size-dependent properties influenced community instability and vulnerability to pert...

Globally benthic invertebrate biotic indices are widely used to assess stream health. In New Zealand, the response of biotic indices to high nitrate-nitrogen (hereafter nitrate) concentrations has not been rigorously tested. We conducted a field survey of benthic invertebrates in 41 lowland intensively farmed Canterbury streams representing a wide...

• Local population characteristics and habitat connectivity both have important influences on metapopulation persistence; however, the relative importance of each can vary depending on the ecological context, making it difficult to apply general ‘rules-of-thumb’ for conservation actions. This is particularly true in dendritic networks, where habita...

Traditionally, resistance and resilience are associated with good ecological health, often underpinning restoration goals. However, degraded ecosystems can also be highly resistant and resilient, making restoration difficult: degraded communities often become dominated by hyper-tolerant species, preventing recolonization and resulting in low biodiv...

Biotic interactions perform an important role in structuring freshwater communities, however these are rarely considered during stream restoration. Degraded stream communities are often dominated by organisms with shell or case protections, such as snails, which are less vulnerable to predation than desired organisms, such as mayflies. Unprotected...

Describing trophic structure within freshwater food webs can be a useful tool for understanding relationships to make ecological inferences and to inform management action. A complementary analysis examining both stable isotope (SI) and biomass community components may be useful, because these two responses may be influenced differently by habitat...

Customary harvests of wildlife underpin the livelihoods, cultural identities, well‐being and ecological knowledge of many Indigenous peoples and local communities (IPLC), whereas government restrictions on harvests can erode these relationships. Supporting IPLC in place‐based resource management, including sustainable customary harvests, can aid wi...

Rapid advances in eradicating invasive species from islands are improving conservation outcomes in these biodiversity hotspots. However, recent conservation gains could be reversed not only by future invasions from non‐native species but also by future extinctions of native taxa, both of which may be facilitated by – or exacerbated by interactions...

• Spatial heterogeneity of abiotic influences like disturbance in riverscapes could play an important role in dispersal‐aided community stability. We tested if higher spatial variability in conditions around river confluences caused by different flood disturbance regimes in branches could possibly influence the stability of a fish assemblage domina...

Aim: We outline a general framework for understanding the dimensions of freshwater disturbances, and highlight their consequences covering individual, population, and community-level effects. Main concepts covered: We distinguish between disturbance drivers and disturbance impacts in a general definition of disturbance, and emphasize the roles of r...

Females of many species of Trichoptera (caddisflies) use pheromones to attract males prior to mating. A diverse array of chemosensory sensilla present on the antennae of both males and females are likely to mediate communication between the sexes. Zelandopsyche ingens Tillyard is a large oeconesid caddisfly, which inhabits small forest streams in t...

In Aotearoa New Zealand, agricultural land-use intensification and decline in freshwater ecosystem integrity pose complex challenges for science and society. Despite riparian management programmes across the country, there is frustration over a lack in widespread uptake, upfront financial costs, possible loss in income, obstructive legislation and...

Given the prevalence of invasive species and high rates of habitat homogenisation across the globe, understanding how these drivers interact to influence native species assemblages is crucial. In river networks, confluences create discontinuities in physical conditions, likely creating hotspots of heterogeneity that influence interactions between n...

In animals with indeterminate growth, such as predatory fishes, mouth size is related to, and increases with, body mass of the organism. As fishes grow in body size, they can consume larger-bodied prey items at potentially-higher trophic levels. Therefore, body size should predict trophic position. Trophic position (TP) is useful for describing ene...

• Understanding risks to aquatic systems posed by changing drought regimes is particularly important for the conservation of already threatened taxa. However, little is known about how local environmental conditions, especially those in heavily human‐influenced situations, interact with regional shifts such as droughts to alter realised impacts on...

1. Conservation translocations—particularly those that weave diverse ways of knowing and seeing the world—promise to enhance species recovery and build ecosystem resilience. Yet, few studies to date have been led or co-led by Indigenous peoples; or consider how centring Indigenous knowledge systems can lead to better conservation translocation outc...

Scale mismatches in social–ecological systems constrain conservation by obscuring signals of environmental change, which could otherwise feed back to inform adaptive responses and solutions. We argue that engaging indigenous peoples and local communities (IPLC) in place-based environmental management could generate the fine-resolution information a...

Reciprocal subsidies link ecosystems into meta-ecosystems, but energy transfer to organisms that do not cross boundaries may create sinks, reducing reciprocal subsidy transfer. We investigated how the type of subsidy and top predator presence influenced reciprocal flows of energy, by manipulating the addition of terrestrial leaf and terrestrial ins...

In freshwater fishes, nitrogen and carbon stable isotopes ratios in tissues commonly reflect the environment in which a fish is feeding, assimilated through its diet. For many species, small-bodied or younger individuals generally feed lower in the food chain, while large-bodied mature individuals feed at higher trophic levels. This is reflected in...

1. Natural and anthropogenic disturbances commonly alter patterns of biodiversity and ecosystem functioning. However, how networks of interacting species respond to these changes remains poorly understood. We described aquatic food webs using invertebrate and fish community composition, functional traits, and stable isotopes from twelve agricultura...

In freshwater fishes, nitrogen and carbon stable isotopes ratios in tissues commonly reflect the environment in which a fish is feeding, assimilated through its diet. For many species, small‐bodied or younger individuals generally feed lower in the food chain, while large‐bodied mature individuals feed at higher trophic levels. This is reflected in...

Introduced aquatic macrophytes can dominate small agricultural waterways in summer and autumn becoming a significant management problem. Excessive growth can clog waterways, causing drainage issues and reducing agricultural productivity while in-stream velocities are reduced and sedimentation increased. Consequently, water managers remove them by m...

Reducing excessive reactive nitrogen (N) in agricultural waterways is a major challenge for freshwater managers and landowners. Effective solutions require the use of multiple and combined N attenuation tools, targeted along small ditches and streams. We present a visual framework to guide novel applications of ‘tool stacking’ that include edge-of-...

ions and diversions are prevalent in river networks worldwide; however, specific mechanisms and measures reflecting changes in functional characteristics of aquatic assemblages in response to flow abstraction have not been well established. In particular, the influence of small takes on fish assemblages is poorly understood. Field surveys and stabl...

Disturbance is a strong structuring force that can influence the strength of species interactions at all trophic levels, but controls on the contributions to community structure of top‐down and bottom‐up processes across such gradients remain poorly understood. Changes in the composition of predator and consumer assemblages, and their associated tr...

Intermittent rivers and ephemeral streams (IRES) may represent over half the global stream network, but their contribution to respiration and carbon dioxide (CO2) emissions is largely undetermined. In particular, little is known about the variability and drivers of respiration in IRES sediments upon rewetting, which could result in large pulses of...

Globally, small agricultural waterways fed by springs, tile drains, and seeps can disproportionately contribute to downstream nutrient loading, which is associated with declines in water quality and ecosystem functions. Treating nitrate using a multiple tool, multiple-scale approach in small waterways could offer improved management of these source...

Excessive nutrient loading from small agricultural headwaters can substantially degrade downstream water quality and ecological conditions. But, our understanding of the scales and locations to implement nutrient attenuation tools within these catchments is poor. To help inform farm- and catchment-scale management, we quantified nitrate export in n...

Both disturbance history and disturbance type act to structure communities through selecting for particular species traits but they may also interact. For example, flooding selects for species with flood‐resistant traits in streams, but those traits could make communities susceptible to other disturbances and so could cause shifts in community comp...

For freshwater systems, climate change‐induced alterations to drought regimes are a considerable threat to already threatened species. This is particularly poignant for kōwaro (or Canterbury mudfish, Neochanna burrowsius), a critically endangered fish largely restricted to drying‐prone waterways on the Canterbury Plains, New Zealand. By comparing t...

Climate change and human pressures are changing the global distribution and extent of intermittent rivers and ephemeral streams (IRES), which comprise half of the global river network area. IRES are characterized by periods of flow cessation, during which channel substrates accumulate and undergo physico‐chemical changes (preconditioning), and peri...

Context Given the importance of spatial heterogeneity in altering dispersal, interspecific interactions, and population persistence, high rates of habitat homogenisation across the globe are a concern. In river ecosystems, confluences likely act as heterogeneity ‘hotspots’ by creating discontinuities in longitudinal processes and influences that ar...

Perennial rivers and streams make a disproportionate contribution to global carbon (C) cycling. However, the contribution of intermittent rivers and ephemeral streams (IRES),which sometimes cease to flow and can dry completely, is largely ignored although theymay represent over half the global river network. Substantial amounts of terrestrialplant...

In the version of this Article originally published, the affiliation for M. I. Arce was incorrect; it should have been: ⁵Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany. This has now been corrected in the online versions of the Article.

Habitat reduction could drive biodiversity loss if the capacity of food webs to support predators is undermined by habitat-size constraints on predator body size. Assuming that (i) available space restricts predator body size, (ii) mass-specific energy needs of predators scale with their body size, and (iii) energy availability scales with prey bio...

Characterisation of food webs, by summarising energy transfer and trophic relationships, allows more functional measurement of ecosystems and may reveal threats (e.g., land‐cover change) in sensitive environments that are not obvious from conventional biomonitoring. However, typical methods used to achieve this are time‐consuming and expensive. The...

Excessive macrophytes can cause significant problems in agricultural waterways requiring active management. Conventional control techniques can have a range of adverse effects. We investigated several control tools in two experiments: firstly, we tested eight treatments at a small-scale (2 m × 2 m). We found intensive hand weeding, weed mat and her...

Natural and anthropogenic disturbances commonly alter patterns of biodiversity and ecosystem functioning. However, how food webs respond to these changes remains poorly understood. Here, we have described aquatic food webs using invertebrate and fish community composition, functional traits, and stable isotopes from twelve agricultural streams alon...

The contraction of aquatic, and expansion of terrestrial, habitats in association with flow cessation and drying in intermittent rivers and ephemeral streams (IRES) fundamentally affect interactions among IRES organisms. Drying alters the relative contributions of autotrophy and heterotrophy to food webs because shredders, microbes, and autotrophs...

Differences in population density between species of varying size are frequently attributed to metabolic rates which are assumed to scale with body size with a slope of 0.75. This assumption is often criticised on the grounds that 0.75 scaling of metabolic rate with body size is not universal and can vary significantly depending on species and life...

The relationship between the total population density (unique fish biomass from sample one + sample two) and the population density caught on the first sample. (DOC)

A segment of my PhD research exploring the hypothesized relationship between the body size of omnivorous and predatory fishes and their stable isotope-derived trophic position

Globally intensive agriculture has both increased nitrogen pollution in adjacent waterways and decreased availability of terrestrially derived carbon frequently used by stream heterotrophs in nitrogen cycling. We tested the potential for carbon additions via leaf litter from riparian restoration plantings to act as a tool for enhancing denitrificat...

The impacts of invasive fish on natural communities have been documented in freshwater ecosystems worldwide. In New Zealand, the most widespread and common invasive fish is brown trout and these fish have caused major changes to both instream processes and the communities that exist in these habitats. This chapter will examine the impact that brown...

PhD research findings, presented in ”Best Student Paper” Symposium

Despite growing concerns regarding increasing frequency of extreme climate events and declining population sizes, the influence of environmental stochasticity on the relationship between population carrying capacity and time-to-extinction has received little empirical attention. While time-to-extinction increases exponentially with carrying capacit...

• Land‐use and climate change could alter the distribution of both native and exotic mosquitoes by changing abiotic and biotic characteristics of freshwater habitats. We initially studied the influence of land use on standing water habitats, and the subsequent effects on native and exotic mosquito and mosquito‐predator presence. • Associated with a...

Contraction of aquatic habitats and expansion of terrestrial habitats associated with cessation of flow and drying in intermittent rivers and ephemeral streams (IRES) change the types, sizes, and abundance of organisms present; the interactions among those organisms; and the overall extent and nature of their trophic interactions – Drying affects m...

Preliminary results from PhD research

The book containing this chapter is available via orders through the New Zealand Hydrological Society for $90 (NZD) plus postage and packaging - see http://www.hydrologynz.org.nz/index.php/nzhs-publications/nzhs-books With 34 chapters and over 100 contributing authors, this book represents a significant review of the current state of New Zealand fr...

PLEASE NOTE: The book containing this chapter is available via orders through the New Zealand Hydrological Society for $90 (NZD) plus postage and packaging - see http://www.hydrologynz.org.nz/index.php/nzhs-publications/nzhs-books With 34 chapters and over 100 contributing authors, this book represents a significant review of the current state of N...

Interacting global-change drivers such as invasive species and climate warming are likely to have major and potentially unexpected influences on aquatic ecosystems. In river networks, modified water temperature combined with patchy physical conditions will likely cause shifts in the amount and distribution of suitable habitat, with influential inva...

Mechanisms underpinning flexible life-history strategies have rarely been tested in hydrologically unpredictable ecosystems where generalists may have life-history trade-offs and developmental constraints that limit their distributions. We investigated in situ nymphal growth and developmental strategies of 2 generalists, Xanthocnemis zealandica and...

Streams form hierarchical, dendritic physical networks, but relatively little is known about how this spatial structure affects community assembly. We investigated interactions between changes over time in macroinvertebrate assemblages and their distribution in space (the space-time interaction) in stream networks. Assemblages were sampled from eve...

Around the world, artificially drained agricultural lands are significant sources of reactive nitrogen to stream ecosystems, creating substantial stream health problems. One management strategy is the deployment of denitrification enhancement tools. Here, we evaluate the factors affecting the potential of denitrifying bioreactors to improve stream...

How different generalist species are able to exploit heterogeneous landscapes likely depends on whether their life‐history strategies confer resilience to multiple environmental selection pressures. We investigated the life‐history strategies of two generalist invertebrates, Xanthocnemis zealandica damselflies and Sigara arguta waterboatmen, which...

Debate about control of interaction strength among species is fueled by variation in environmental contexts affecting food webs. We used extensive surveys and two field experiments to testthe individual and interactive influences of variation in the assemblages and associated traits of grazers as shaped by the legacy of disturbance, nutrient limita...

The influence of capture interval on trap shyness, and temperature, rainfall and drought on capture probability (p) in 827 brown mudfish Neochanna apoda was quantified using mark–recapture models. In particular, it was hypothesized that the loss of trapping memory in marked N. apoda would lead to a capture-interval threshold required to minimize tr...

Biodiversity in running waters is threatened by an increased severity and incidence of low-flow extremes resulting from global climate change and a growing human demand for freshwater resources. Although it is unknown how and to what extent riverine communities will change in the face of these threats, considerable insight will be gained from effor...

Traditional productivity-diversity theory predicts that eutrophication will result in greater species richness due to increased resources at the bottom of the food web. However, few studies on the effects of increasing ecosystem productivity on biological communities have included responses at multiple trophic levels. We hypothesized that the effec...

Previous studies of invertebrate responses to hydrological disconnection from the flow and drying have focussed on habitats with long hydroperiods (dry slowly after disconnection, i.e. months to years). We focus here on the effects of short hydroperiods (dry rapidly after disconnection, i.e. hours to days) on river invertebrate communities and inse...

Abstract Context Metacommunities are sets of local communities linked by dispersal. Their characteristics are defined by both large-scale spatial processes such as dispersal, and local environmental processes, although which factors are likely to predominate in a given situation is poorly understood. Objectives We investigated whether flow regime a...