A fish story: climate change bigger threat to lakes that predator fish

From the UNIVERSITY OF GUELPH and the “obviously they’ve never encountered a Northern Pike outside of a model” department comes this ridiculous study that is nothing more than speculation based on a model of their own design.

Esox lucius (Northern Pike) caught in Belgium Image: WikiPedia

Monitor climate change, not predators, to protect lake diversity: Study

Climate change and other environmental factors are more threatening to fish diversity than predators, according to new research from the University of Guelph.

It is a surprising and important finding, as humans rely upon freshwater lakes for more than one-fifth of their protein needs worldwide, says lead author Prof. Andrew MacDougall in U of G’s Department of Integrative Biology.

“Freshwater is a huge source of food for people, including Ontario’s Great Lakes,” he said.

Lakes, rivers and streams cover less than one per cent of Earth’s surface but provide 12 per cent of human fish consumption, MacDougall said.

The findings, published this month in the journal Nature Communications, may offer ideas for resource managers to better protect all-important species diversity in lakes around the world, MacDougall said.

His international research team included U of G biologist Prof. Kevin McCann and scientists in Canada, Switzerland, Sweden, Australia, the United States and Japan.

The research team modelled prey-predator interactions and environmental factors, such as lake size, temperature and water quality.

The scientists used information compiled earlier by the Ontario government on more than 700 lakes in the Great Lakes watershed.

The team found that species diversity depends more on “bottom-up” environmental factors than on “top-down” interactions, or which fish species eats what – a result that surprised MacDougall.

He said food chain interactions among organisms are still important.

“All lakes have big predators, and predators always kill lots of fish that they consume,” said MacDougall. “But the strength and degree of the interactions seems to depend fully on environment. The interactions are never independent of lake conditions.”

He said resource managers need to pay attention to physical conditions, including lake warming caused by climate change and water quality impacts of human activities such as farming.

The authors say the paper’s findings set a baseline for species diversity in southern Ontario lakes. That will help resource managers monitor or predict those effects as well as the impacts of other changes such as introduction of invasive species.

Many freshwater fish species in Canada and abroad are already endangered by human-caused environmental changes, said McCann. “There’s a looming threat of loss of species.”

He said the study shows how so-called big data can help detect patterns in complicated ecosystems and how precision agriculture – including more targeted use of crop fertilizers — may lessen pollutants entering lakes and streams.

Big data and precision agriculture are key aspects of the University’s Food from Thought project, which aims to help find sustainable ways to feed Earth’s growing human population. McCann co-leads that project, launched in 2016.

U of G researchers in the new study were supported by funding from the Natural Sciences and Engineering Research Council and from the Canada First Excellence Research Fund for the Food from Thought project.


The press release from the University of Guelph did not contain a link to the paper, but did contain the journal reference “Nature Communications”. A cursory search didn’t reveal the paper. But an advanced search did. I don’t know why these Uni PR people don’t include direct links to the paper.


Context-dependent interactions and the regulation of species richness in freshwater fish

Species richness is regulated by a complex network of scale-dependent processes. This complexity can obscure the influence of limiting species interactions, making it difficult to determine if abiotic or biotic drivers are more predominant regulators of richness. Using integrative modeling of freshwater fish richness from 721 lakes along an 11olatitudinal gradient, we find negative interactions to be a relatively minor independent predictor of species richness in lakes despite the widespread presence of predators. Instead, interaction effects, when detectable among major functional groups and 231 species pairs, were strong, often positive, but contextually dependent on environment. These results are consistent with the idea that negative interactions internally structure lake communities but do not consistently ‘scale-up’ to regulate richness independently of the environment. The importance of environment for interaction outcomes and its role in the regulation of species richness highlights the potential sensitivity of fish communities to the environmental changes affecting lakes globally.

Here’s their model:

Direct and indirect drivers of species richness in fish. SEM-derived multivariate relationships among integrated abiotic and biotic regulatory factors (blocks = degree days, circles = lake morphometry, triangles = water quality, and biotic factors [red lines]) for the richness and composition of four major fish functional groups in 721 lakes along an 11° latitudinal gradient in Ontario, Canada SEM integrative model:, n = 648, MLEST = 4.91, Degree of freedom = 13, P = 0.977, see Methods and Supplementary Note 1). Solid lines indicate negative relationships; dashed lines indicate positive relationships. Arrows indicate the direction of the relationship. Bold lines indicate stronger relationships, arbitrarily assigned as standardized path coefficient values > 0.40. Black lines indicate abiotic influences on biotic factors and red lines indicate influences between biotic factors. Functional groups are predator, littoral, pelagic, and small-prey species, with full species list given in Supplementary Table 1

And here is the results:

Frequency of negative, positive, and non-associated pair-wise interactions between among-lake richness versus within-lake abundance. a Frequency of significantly positive, nonsignificant, and negative associations among 231 species pairs of freshwater fish in 721 lakes, for two classes of data: lake presence/absence (differences in among-lake richness) and lake abundance based on catch per unit effort for each species in each lake (differences in within-lake abundance). We hypothesized an increase in the frequency of negative interactions within-lakes but this was generally not the case, for both species pairs in the ‘same’ temperature class (e.g., two species of ‘warm-water’ fish, Supplementary Table 1) versus ‘different’ classes (warm vs cold-water species). b Relative change in the importance of four major explanatory factors (climate, morphometry, water quality, and negative species interactions) between BRT analyses of among-lake richness to BRT analyses of within-lake abundance (see Supplementary Table 3). Significant thresholds were based on an α < 0.05

I read the entire study, and noted this:

Our analysis is one of the more comprehensive empirical tests of the importance of limiting species interactions for regulation of richness and composition, using integrative analyses and fish data from 721 lakes covering large gradients of degree days, latitude, lake morphometry, water quality, and trophic complexity. Although we detected evidence of significant influences of species interactions on diversity and composition, negative interactions in isolation were unable to consistently predict co-occurrences along multiple regional-scale environmental gradients—fish appear to rarely forbid one another from lakes. This conclusion does not indicate that antagonistic species interactions are unimportant for the regulation of fish communities, rather it implies that it is difficult to detect independent signals of their influence on species richness among lakes. Indeed, dozens of studies have explored richness regulation in fish, driven by interest in both fundamental ecological mechanisms and fisheries management. Our work provides clarification on why these questions have been difficult to test, with richness regulated by complex multivariate factors that operate at a range of spatial resolutions.

Our findings were robust, with similar results for the presence-absence of species pairs among lakes versus the analysis of species abundance within lakes.

Any time someone writing a climate related paper claims their finding are “robust”, my BS detector immediately goes off.

There’s two important things missing from this paper:

  1. They cite degree days as the metric for climate change. In the real-world, while degree days do have a climatic component they are also a weather driven phenomenon. They fail to recognize this outside of their model.They assume that weather won’t change with changes in degree days.
  2. They assume no species adaptation to “climate change”, if fact the entire paper does not contain the words “adapt” or “adaptation”. That’s a fatal assumption.

In my opinion, this study is garbage, with the PR written as a climate headline grabber.

However, they didn’t publish the data, even though they say the data is available. So perhaps somebody with species experience can request it and test it to confirm my opinion.

Data availability
The data were collected through Ontario’s BsM program and are available upon reasonable request to the Aquatic Research and Monitoring Section, Ontario Ministry of Natural Resources and Forestry, 2140 East Bank Drive, Peterborough, Ontario, Canada K9J 7B8.


via Watts Up With That?


March 23, 2018 at 11:24AM

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