All posts by oldenlab


Transferring flow-ecology knowledge

The San Juan River Basin is fortunate to have an extensive monitoring program that informs managers on how species respond to changes in streamflow. Can we leverage this knowledge for rivers where responses are not as well known? Photo credit: Rachel Lee

Environmental flow assessment is an emerging approach for balancing the water needs of freshwater ecosystems with the water needs of human society. By using knowledge of how freshwater species respond to patterns in streamflow (i.e. their flow-ecology relationships), scientists and managers have been able to use environmental flows to improve native fish spawning and recruitment, restore assemblages of native macroinvertebrates, and promote native riparian vegetation over invasive ones.

But what if we do not have the knowledge of species’ flow responses when we need to implement environmental flows? Because streamflow is so integral to the structure and function of riverine ecosystems, most environmental flow assessments are built on a foundation of understanding species’ flow-ecology relationships. Lacking this foundation may make environmental flows ineffective or even detrimental to the freshwater ecosystem we’re trying to sustain. On the other hand, the problems of increasing water scarcity and growing human water consumption will not wait for the development of the flow-ecology models necessary to prescribe effective environmental flows.

To address this challenge, we are investigating the transferability of species’ flow-ecology relationships across different locations and through time, using a suite of freshwater fishes across five river systems in the American southwest. We are also evaluating use of traits as a currency for transferring flow-ecology knowledge across different species, which can inform management of rarer species that are less likely to have established flow-ecology research.

Fortunately, it turns out that the transferability of species’ flow-ecology relationships is similar across spatial scales, meaning flow-ecology models can likely be transferred across river systems. Knowledge of a species’ flow response at a given location is relatively transferable across time as well, suggesting that we do not need to prioritize the constant verification of flow-ecology models. Finally, flow-ecology relationships appear to be similarly transferable across species of the same trait guild as they are within species, offering the opportunity to share information across taxonomic divides.

This all bodes well for implementing needed environmental flows even when flow-ecology knowledge is limited. We’re currently writing the manuscript for this work, so be on the lookout for the publication!

- Will Chen


Rusty crayfish: front lines are moving fast

A large male rusty crayfish from Magone Lake by the John Day River waiting to be measured and weighed. Photo: J. Olden.

What freshwater bug is 3-inch long and crawls downriver nearly 10 miles a year and eat everything on its path? Answer: invasive crayfish.

Two years ago, Laura Twardochleb from the Olden Lab published a comprehensive meta-analysis of the literature to summarize the extent of damage that non-native crayfish cause to freshwater ecosystems. She found that because of their omnivory and role as ecosystem engineers, non-native crayfish consistently lead to ecosystem-scale effects where they are introduced, regardless of species. Recently, the Olden Lab started to investigate the invasion of rusty crayfish (Orconectes rusticus) in the John Day River, a major tributary of the Columbia River in Oregon, to better grasp crayfish invasion dynamics. Discovered in 2005, this introduction is the first recorded occurrence of rusty crayfish west of the continental divide, and is likely a result of a release by a nearby school. From 2005 to 2010, rusty crayfish spread downstream at an average rate of 13.5 km/year (Sorenson, 2012).  Given wide-ranging ecological effects in its non-native range and its rapid spread through Pacific salmon rearing habitat, there is considerable concern regarding O. rusticus in the region.

For my Master’s thesis, I am developing a model to estimate spread of rusty crayfish in the John Day River from the time of introduction until now based on its observed distribution in 2005 and 2010. I will then use this calibrated model to predict the future spread of rusty crayfish throughout the watershed until 2020. I will also use this model to test whether control measures such as trapping crayfish or the release of sterile males in the population could be effective in slowing its spread.

To validate my predictions, we conducted an extensive field survey for rusty crayfish in the John Day River in August 2016. We found that wherever rusty crayfish occurred, the native species of signal crayfish (Pacifastacus leniusculus) had been extirpated. We also found that rusty crayfish had dispersed more than 200km downstream since being introduced and is now spreading faster downstream than predicted by our initial model. This discrepancy between our predictions and observations could mean two things. First, rusty crayfish might respond to some environmental conditions more strongly as they spread downstream: for example, crayfish may display faster metabolism and rates of dispersal as they reach warmer waters downstream. Second, individuals at the “front lines” of the invasion may be dispersing faster than before. This second possibility is of particular interest as several studies have shown that rapid evolution can take place in invading populations, leading to accelerating invasion rates and increased impacts on the native communities. For instance, Cane toads (Rhinella marinus) at the leading edge of the invasion wave in Australia have been developing heritable morphological (longer hindlegs), physiological (more endurance), and behavioral traits (more often in movement) that allow them to spread faster, straighter, and for longer periods of time.

For crayfish as well, a handful of studies have reported changes in sex and age composition, behavior, morphology, and physiology between core and edge invading populations in rivers. Therefore, I also plan to investigate whether the population structure, morphology, or diet of rusty crayfish individuals at the leading edge of the invasion is different than that of those populations near the introduction site. I hope that this will allow us to better understand the drivers of the invasion patterns observed in crayfish invasions and give us an insight into the potential consequences for this valuable river ecosystem.

- Mathis Messager


Dams, scarcity, and social-ecological resilience

Glen Canyon Dam (1963) had a tremendous ecological effect on the Colorado River, but offers socio-economic benefits like water storage and distribution, hydropower, and recreational opportunities. Glen Canyon National Recreation Area (pictured above) extends 1.25 million acres between Lees Ferry in Arizona to the Orange Cliffs of southern Utah. Can we trade-off socio-economic benefits with efforts to restore flow regimes?

We know that dams are a paramount driver of hydrological alteration, homogenizing regional river dynamics and biodiversity. However, dams also provide a range of socio-economic benefits, and under scenarios of water scarcity due to climate change and over-allocation of freshwater resources, it is increasingly important to ask how dams may provide engineered resilience to dependent social and ecological systems.

I am Albert Ruhi, a community ecologist motivated by applied questions about how freshwater biodiversity is responding to global change. I am a new Postdoc Fellow in the National Socio-Environmental Synthesis Center (SESYNC), working on a project that focuses on the interaction between dams, water scarcity, and freshwater biodiversity, and that has Julian Olden as an external mentor. My project examines two questions: 1) Where are the battlegrounds of water scarcity in the U.S., defined as watersheds (HUC-8) where dams have a disproportionately high impact on hydrological and ecological alteration?, and 2) Can we identify optimal trade-offs between maximizing water conservation in reservoirs (to increase human resilience to water scarcity) and securing as much biodiversity insurance as possible?

I plan to answer these questions applying time-series methods on long-term physical (streamflow), ecological (fish spatial data), and socio-economic data. These two questions combined should illuminate how dams may provide engineered resilience in river basins via controlled river flow manipulations. Stay tuned!

- Albert Ruhi

Saffron Shiners, photo by Freshwaters Illustrated

What makes a species rare?

In a community, it is almost always true that some species are common while most are rare. This pattern is demonstrated by plotting species abundance distributions (see Magurran 2003 or Verbeek 2014 for excellent overviews) observed in many real life communities. Local abundance is not the only facet of rarity – species can also be defined as rare or common in terms of their overall geographic range and its habitat breadth. The late Deborah Rabinowitz, (a professor of Ecology and Systematics at Cornell), was the first to highlight and study the multidimensional nature of species rarity (Fig. 1).

Understanding the connections between different kinds of rarity and their respective drivers could help us better understand how species survive across multiple spatial scales. Perhaps more important is the potential to identify and predict which species will be imperiled by more than one kind of rarity.

Other studies have often observed a positive correlation between local abundance and geographic range size (see reviews here and here by Kevin Gaston, Tim Blackburn, and John Lawton; the latter, in particular, is a great book that contains critical examinations of many macroecological concepts and hypotheses that continue to be highly relevant today, 16 years since its publication).

Fig. 1. Three dimensions of rarity: range size (blue polygons), habitat breadth (different habitats denoted by different shades of grey), and local abundance (orange points). In this example, species B is rarer in all three dimensions than species A. A “triple extinction jeopardy” occurs when there is a general concordance in the three rarity dimensions across all species occurring in a given geographic region.
Fig. 1. Three dimensions of rarity: range size (blue polygons), habitat breadth (different habitats denoted by different shades of grey), and local abundance (orange points). In this example, species B is rarer in all three dimensions than species A. A “triple extinction jeopardy” occurs when there is a general concordance in the three rarity dimensions across all species occurring in a given geographic region.

Two hypotheses were relatively well-supported: the niche breadth hypothesis formulated by James H. Brown, and the niche position hypothesis developed by Richard Gregory and Kevin Gaston. In the first hypothesis, niche breadth drives both local abundance and geographic range size. In the second hypothesis, the authors argued that niche position (not breadth) underlie abundance and range, in which species that use the most common niches would achieve the greatest local abundance as well as range size. Investigations into these hypotheses have mostly focused on terrestrial or marine communities. Because freshwater stream systems are substantially different from both terrestrial and marine systems—for one thing, dispersal of a species greatly depends on its position in the stream network—we wanted to examine the mechanisms that govern rarity in freshwater fish.

To do this, we used a dataset of freshwater fish communities occurring in natural stream sites across the US. This dataset was previously used to show that environmental filtering (and secondarily, predation) but not competition drive community assembly in freshwater fishes. We limited our analysis to the stream sites that were not dominated by non-native species, and used phylogenetic regression and path analytic models to figure out how local abundance, niche (habitat) breadth, and range size of species occurring in these sites relate to one another. Through our analyses, we uncovered potential mechanisms by which species life history, habitat affinities, and biogeography drive variation in the three rarity dimensions.

So what did we find? Well, we found while habitat breadth drives both local abundance and geographic range size, the latter two variables were not positively correlated. As for why is that so, I’ll leave it as a mystery for now (a clue, which is perhaps already obvious to you, is that species life-history and ecological traits are really key to this finding). Overall, our results support the notion that macroecological dynamics in freshwater stream communities are indeed quite different from terrestrial or marine communities.

We are currently finalizing the manuscript for submission so watch this space for updates!

- Xingli Giam

A Mountain Whitefish swims over river bedrock

Share your story: World Fish Migration Day 2016

Fish Can’t Travel Like We Do! Downloadable postcard from World Fish Migration Day website

Call for videos – deadline extended to May 7th!

Migration plays a central role in the life cycle of many fish species. For feeding, reproducing, or simply completing their life cycle, fish sometimes need to move long distances, within freshwater environments or between marine and freshwater systems. Well-known fish such as eels, salmons, and sturgeons in waters of North America and Europe are only a few examples out of thousands of migratory species, found everywhere from tropical rivers to intermittent streams of Australia. For example, the longest freshwater fish migration is made by the giant Amazonian catfish Brachyplatystoma rousseauxii commonly called the Dorado, which travels up to 2,500 miles from nursery habitats in the Amazon River estuary near the Atlantic Ocean to spawning sites in the Andean headwaters of Bolivia and Colombia. Once it has spawned, it goes back to the estuary.

Human activity is severely threatening migratory fish species worldwide, mainly through the construction of man-made obstacles like dams, weirs, and sluices. Although dam construction slowed somewhat after the development frenzy in the second half of the twentieth century, a new boom is projected in coming decades and will affect some of the most diverse and untouched rivers of the world like the Amazon, the Mekong, and the Congo river. On the Mekong river alone, more than ten dams are under construction or planned on the mainstem, and up to 70% of Mekong fish are thought to be migratory, putting at risk  food and revenue for millions of people in the region.

World Fish Migration Day is a global event which is designed to bring awareness to these kinds of stories, and improve the public understanding of the importance of connected rivers. As part of this global celebration, the Olden Lab is partnering with Society for Conservation Biology Freshwater Working Group, and the World Fish Migration Foundation to create a 24-hour streaming video event which celebrates free flowing and connected rivers around the world. We are requesting submissions of short video diaries from people around the world about what their river means to them and their community – these videos will be compiled and streamed on May 21st.

If you have a story to share, we’d like to hear from you! All formats are accepted, and we can provide simple instructions to create a short narrated video about a river in your area. For more information about this event and instructions to create and upload a video, check out the PDF about the event or email Lauren Kuehne at with questions or trouble with uploading.

Largemouth Bass suspend below Bleeding Shiners

Niche conservatism: which niche matters most?

Niche conservatism - or the degree to which plants and animals retain their niches and related ecological traits through space and time – is a classic concept in ecology receiving renewed interest in recent years. This is partly because of its relevance to predicting species’ responses to global change, since a tendency toward conservatism would mean that species have only a limited capacity to adapt to new environmental conditions. Those species would be particularly vulnerable to environmental change.

Bluegill sunfishes (Lepomis macrochirus) success is partly ascribed to flexibility in foraging, an aspect of the Eltonian niche.
Bluegills success  in diverse areas is partly ascribed to flexibility in foraging, an aspect of the Eltonian niche. Photo: Freshwaters Illustrated.

Conversely, conservatism also implies that spread of invasive species is limited by the environmental conditions of their native ranges, laying robust foundations to predict the extent of potential invasions. In support of this view, Lavergne et al. (2013) showed that declines of European bird species over the last decades were related to their past rates of climatic and habitat niche evolution, suggesting that the degree of niche conservatism may be pivotal for forecasting invasion risk and biodiversity changes.

With intense scrutiny, however, niche conservatism is also the subject of considerable debates. This is probably not surprising given that niche conservatism relies on the concept of ecological niche – a major but fairly abstract and complex theoretical concept in ecology and evolution. The original definition of ecological niche by Hutchinson focuses on two different dimensions of species niches, namely the condition and resource axes allowing species persistence. These correspond to the Grinnellian and Eltonian niches of Soberón (2009). The Grinellian niche focuses on the abiotic conditions which are favorable to the survival and reproduction of individuals, whereas the Eltonian (or biotic) niche focuses on a species’ position in an ecological network and encompasses both biotic interactions and resource availability. While most literature has focused on the Grinellian niche (often

Globally successful invaders such as brook trout offer “experiments” to examine how aspects of the Grinellian niche (e.g., thermal tolerance) may limit species’ ability to adapt to new environments. Photo by Freshwaters Illustrated.
Globally widespread invaders such as brook trout offer “experiments” to examine how aspects of the Grinellian niche (e.g., thermal tolerance) may limit species’ ability to adapt to new environments. Photo: Freshwaters Illustrated.

from a climatic perspective) it is important to remember that the niche is multi-dimensional. Depending on the variables and methodology used to measure species’ niches, the conclusions about niche conservatism can greatly vary. And as the study of Lavergne et al. (2013) above suggests, conservatism of different aspects of species niches and related traits may be needed to fully understand ability of species to cope with global change. Given that the consequences of altered biotic interactions are expected to be superimposed on abiotic changes, the Eltonian niche may be especially useful in forecasting the overall response of species to new environments.

Using both facets of the Hutchinsonian niche, we are currently investigating links between past rates of niche evolution and contemporary patterns of niche conservatism for freshwater fish invaders. Contemporary biological invasions provide valuable replicated experiments to assess the degree of niche conservatism across a broad range of environments and taxonomies. This research aims to advance knowledge of the extent to which niche evolution contributes to invasion success as well as the vulnerability of species under global environmental change.

- Lise Comte


Saving the Australian Lungfish – through its stomach

Australian lungfish, one of the world’s oldest living vertebrates. Photo by Alice Clement.

The Australian lungfish, (Neoceratodus forsteri), is one of only five extant lungfish species in the world. It is a member of the oldest living vertebrate genera on the planet, with fossil records dating back 380 million years. At one time distributions extended to the center of the Australian continent, but at present only the Australian lungfish remains in a small number of rivers of southeast Queensland. Australian lungfish is a sacred (totemic) fish of the Gubbi Gubbi Aboriginal people who have revered and protected it for thousands of years.

Despite being federally-listed, the long-term persistence of the Australian lungfish is in severe jeopardy. Rivers supporting lungfish have been modified and degraded by numerous anthropogenic impacts, threatening the persistence of remaining populations; as a result, lungfish has been listed as ‘vulnerable’ under Australian Commonwealth Legislation. Conservation efforts to ensure the global persistence of the globally-unique and nationally-threatened lungfish species is hampered by lack of information on their foraging ecology over space and time. Traditional (lethal) methods of dietary analysis are inappropriate for threatened species and offer only a brief snapshot of feeding habits.

With support from The National Geographic Society, The Mohamed bin Zayed Species Conservation Fund, and the American Philosophical Society, we are applying innovative nonlethal techniques to assess long-term changes in lungfish trophic ecology. Lungfish can live up to 80 years; working with partners in Australia we are combining novel radiocarbon aging techniques with stable isotope analysis in different regions of fish scales. This will allow us to assess changes in lungfish resource use over long time periods and in response to anthropogenic pressures (flow alteration and land use) in the last two rivers supporting native populations of Australian lungfish.

Collectively, this project will inform resource and movement requirements for Australian lungfish, allowing the impacts of catchment disturbance and threatening processes to be quantified and managed.

Project Goal Statement: To support the conservation and persistence of Australian lungfish through innovative stable isotope techniques, allowing analysis of changes in resource use over long time periods and in response to land use and flow alterations.

Project timeline: September 2013 – September 2016

Project partners and links:
Mohamed bin Zayed Species Conservation Fund, 2014 Annual Report Profile
American Philosophical Society
National Geographic Society

Mudminnows are small (

Chehalis River: endemic fish and non-native plants

Non-native aquatic plants can have far reaching and unforeseen impacts on habitat for fish, invertebrates, and other wildlife; however, logistical constraints often don’t allow for investigation of impact across multiple trophic or community levels. The lack of comprehensive information regarding impact of non-native plants on aquatic ecosystems can hinder managers’ ability to prioritize management resources. The Chehalis River is an excellent system to investigate some of these dynamics as is it home to a diverse community of economically and culturally important fish species; like many rivers and lakes in Washington, it is also home to several non-native aquatic plants, namely non-native parrotfeather (Myriophyllum aquaticum) and Brazilian elodea (Egeria densa).

Aquatic plants – like non-native parrotfeather shown here – can dramatically alter physical and chemical characteristics of fish habitats

The Chehalis River Basin also encompasses a majority of the distribution of Olympic mudminnow (Novumbra hubbsi), Washington State’s only endemic fish species; Olympic mudminnow also have the dubious distinction of having the smallest range of any mudminnow species in the world. Listed as ‘Sensitive’ by Washington State Department of Fish and Wildlife in 1999, there is nonetheless a very sparse understanding of population sizes and environmental drivers of habitat suitability and occupancy for this species. Without this information, it is difficult to design effective management plans for long term sustainability and conservation.

With funding from the Washington State Department of Ecology, in 2013 we initiated a field-based project to measure the ecological impacts of non-native parrotfeather on fish habitats in the Chehalis River. Over two years we comprehensively sampled 22 sites on the Chehalis River, measuring plant, invertebrate and fish communities as well as water quality in response to invasion by parrotfeather. These sites were also selected based on suitability for occupancy by Olympic mudminnow, which we chose as a focal fish species.

Products from this project include a review article focused on the ecology and conservation of the five species of mudminnow worldwide and a research article describing the environmental drivers of occupancy and detection of Olympic mudminnow on the Chehalis River (article in press). A third article (in preparation) will focus on the ecological impacts of non-native parrotfeather on fish habitats across multiple community levels.

We are continuing our research in the basin with sampling in 2015 and 2016; this sampling will focus on describing the extent and distribution of non-native parrotfeather in riverine and adjacent habitats of the Chehalis River. The distribution and spread of parrotfeather is being investigated in multiple years in relation to local and landscape scale drivers of presence and persistence. We are also working with project partners to test the efficacy of management and control options in context of these environmental drivers.

Like other mudminnow species, Olympic mudminnow are decided habitat specialists, preferring shallow and densely vegetated wetlands

As a whole, our work in the Chehalis River is intended to advance the science-based management and conservation of Olympic mudminnow, while also furthering our understanding of the impacts of non-native aquatic plants on sensitive fish habitats.

Project Goal Statement: To evaluate the ecological impacts of non-native aquatic plants on fish habitat in the Chehalis River, as well as establish the current distribution and projected spread of parrotfeather in the Chehalis River Basin. The goals related to Olympic mudminnow are to identify new riverine populations along the Chehalis River, investigate the environmental drivers of occupancy and detection, and guide development of standardized sampling and monitoring protocols for this highly endemic species.

Project timeline: June 2013 – June 2017

Project partners and related links:
Washington State Department of Ecology
Washington State Department of Fish and Wildlife
Washington State Department of Natural Resources
Thurston County Noxious Weed Department


Review article in FisheriesEcology and conservation of mudminnow worldwide” and related blog post

Research article in Transactions of the American Fisheries Society “Environmental drivers of occupancy and detection of Olympic mudminnow”

Poster presented at the Meeting the Challenge conference on impacts of non-native parrotfeather



Ecological integrity in freshwaters

The term “ecological integrity” became a linchpin of freshwater management and conservation in 1972, when it was mandated as an objective in the U.S. Clean Water Act (Section 101, “to restore and maintain the chemical, physical and biological integrity of the Nation’s waters.”) Since that time, large amounts of research has been devoted to methods of assessing the status and condition of freshwater systems using the currency of ecological integrity. Although the concept largely originated with the Clean Water Act, its utility as both a legislative framework and a general conservation ethic has led to inclusion as a guiding principle in monitoring and assessment of freshwater, marine and terrestrial ecosystems worldwide.

Funded by the U.S. Fish and Wildlife Service, the Olden Lab is leading a comprehensive review project of assessment methods and strategies for freshwater ecosystems. Although assessment methods have been reviewed periodically in the past for specific habitats, our review process will examine methods and assessment trends across all freshwater ecosystem types (lakes, wetlands, streams, and riparia) across a large geographic extent (North America). We are accomplishing this through a systematic review of peer-reviewed and grey literature, as well as examination of emerging approaches being developed by projects funded by the national network of Landscape Conservation Cooperatives (LCCs).

We are also taking advantage of the LCC network to access much needed expert, interdisciplinary knowledge related to how assessment results are used and translated. Assessment of ecological integrity is only half of the battle; the real challenge is designing assessments which support and facilitate conservation and management actions. To gather practical experience and opinions, we implemented a national survey of conservation and management professionals; this survey is nearly complete and will be contrasted with the results of the literature review.

Overall, the comprehensive and systematic review process will allow us to identify and recommend methods and frameworks which are well suited to individual ecosystem types, and particular management contexts and questions. A second objective is to identify data and knowledge gaps which will advance and facilitate particularly promising methods.

Project Goal Statement: To identify status and trends in assessment of North American freshwaters, recommend best practices for evaluating aquatic ecological integrity at different landscape scales, and identify data and knowledge gaps which would support future assessments and conservation of freshwater ecosystems.

Project timeline: August 2014 – January 2016

Project partners and related links:
Landscape Conservation Cooperatives (LCCs)
United States Fish and Wildlife Service
Project webpage (and interim documents) on Griffin Groups

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Amazon freshwater fish in a changing climate

Zebra pleco (Hypancistrus zebra), a highly endemic  catfish from the Xingu River, which is critically endangered.  Photo: Leandro Souza.
Zebra pleco (Hypancistrus zebra), a highly endemic
catfish from the Xingu River which is critically endangered.
Photo: Leandro Souza.

In general when we think about climate change, most people think about cold water species, but warm water species could be also be affected. The Amazon River Basin is an enormous area expected to be affected by climate change; approximately 7 million km2 of dense river network with the largest number of freshwater fish species anywhere in the world. The Amazon is home to more than 2,000 freshwater fish, including highly unique, economically, and culturally important species.

According to the Intergovernmental Panel on Climate Change (IPCC) scenarios the Amazon will be warmer and drier in the future; this in turn is likely to lead to changes in flow regimes. Some species in the Amazon may be highly adapted to and dependent on current flow regimes, and modifications as a result of climate change may have direct consequences for breeding, migration and persistence of fish species. Currently the Brazilian Amazon has 71 threatened freshwater fish species due to the impacts of dams, pollution, mining and urbanization. There is little or no knowledge as to how sensitive these species are to climate change impacts, or how climate change may interact with other stressors to affect fish in the Amazon.

Despite the diversity of freshwater fish found in the Amazon, it is an area with very large knowledge and research gaps. To understand the potential impacts of climate change on freshwater fish in the Amazon, we created a survey to gather information from fisheries experts working in the Amazon. Our objective is to evaluate the sensitivity and vulnerability of the 71 threatened freshwater species in the Brazilian Amazon to future climate change impacts. The research is still in progress, but preliminary results suggest that the majority of threatened species will be highly sensitive to climate change impacts.

There are currently very few published research studies about the impacts of climate change on freshwater fish species in tropical areas. The results from this survey will help environmental agencies who are responsible for management and conservation of threatened fish species in Brazil.

- Renata Frederico, Visiting Researcher