Tag Archives: Ecology

Scepticism towards the Living Planet Index is unwarranted

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The most recent Living Planet Report was released last year, which showed that vertebrate populations around the world have declined by 68% on average. At the time, Brian McGill wrote a post at Dynamic Ecology expressing his scepticism over these large declines. His doubts stemmed from several related papers, which all showed that vertebrate populations tended to be quite stable on average. While some populations have declined, most have remained stable and others have actually increased.

My understanding of Brian’s message (and the messages of the published papers supporting him) was that while humans do affect vertebrate populations, these effects are not consistently negative. Instead, some species benefit from human actions, so human’s ultimate legacy will be rearranging relative population structure, rather than causing wholesale declines.

While I agree with this interpretation, I worry that it is causing unwarranted mistrust of the Living Planet Index. I was reminded of this last week by a passing comment by Mark Vellend:

“If biodiversity seems intractable, then just think about recent discussions of the Living Planet Index, which is based on pretty simple underlying data.”

His remark was in the context of his post suggesting that ecologists have subconscious biases that cause us to exaggerate how much humans harm biodiversity. Ecologists probably do have subconscious biases, but the Living Planet index shouldn’t be used as evidence of this.

I don’t believe the Living Planet Index exaggerates population declines. However, I also recognise that populations are stable on average. This probably seems contradictory, so I’ll use the rest of this post to explain why it isn’t.

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Scientific journals should be judged, not ranked

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Aspiring scientists quickly learn that where they publish their hard earned data is important for career progression. A paper in a prestigious journal pushes them up the professional ladder faster than the same paper in an obscure one.

This has led to an obsession with quantifying the prestige of a journal using impact metrics. Over at Conservation Bytes, Corey Bradshaw presents a RShiny App to rank ecology and conservation journals using a composite of different citation metrics. His app is based on a published paper, so you can be sure that it technically sound. It is not my intention to criticise these efforts; if you want to rank jounals, then this composite approach is definitely the way to go.

However, I don’t think there is much to gain from ranking journals based on their impact metrics. Moreover, scientists – especially early-career scientists – would be better off judging journals based on whether is will ensure that their paper reaches the right audience.

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Trump’s Wall could affect 350 species of amphibians, reptiles and mammals

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I originally started writing this post two years ago, back when Donald Trump had just been elected as President of the USA. I didn’t finished writing it then because I assumed that the topic was just a passing fad, something none of us actually took seriously. Fast-forward to today, the US government has been shut down for more than three weeks as Trump tries to hold the country hostage over his border wall with Mexico. I suppose now is a as good a time to finally publish this post, even though a paper was published on the topic in BioScience last year.

As one of the most absurd campaign promises in recent history, Donald Trump’s commitment to building a wall between the United State and Mexico has attracted many critics. Many scoffed at his claims that such a structure will keep out the make-believe mob of bad hombres chomping at the bit to sell drugs to innocent Americans. Others giggled at Trump’s conviction that those very same bad hombres would pay for his trademark erection.

But this post is not about the fragile justification for building a massive wall. It’s a thought experiment on how many species would be affected by this cross-continent barrier.

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Training well-rounded and work-ready ecologists

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Over at the Ideas for Sustainability blog, Chris Ives wrote an excellent overview  of a recent paper about developing a translational ecology workforce. Briefly, the paper states that we need a work force that has the right combination of (1) multidisciplinary knowledge, (2) practical skills and (3) personal aptitudes.

Multidisciplinary knowledge focuses on traditional academic disciplines, like ecology, law, economics, governance, ethics and sociology. It emphasises T-shaped knowledge, where a deep understanding of a narrower sub-discipline (the vertical line of the T) is married to a more general appreciation of a wider range of topics (the horizontal line of the T).

Practical skills refer to the ability to actually get things done. This includes skills like effective communication, risk assessment, conflict resolution or project management.

Finally, personal aptitudes are those – often intangible – personality traits that make people good to work with. These aptitudes include things like patience, humility, trustworthiness, leadership, punctuality, reliability etc. Continue reading →

Boasting about backyard biodiversity

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The easiest way for an aspiring naturalist to explore wildlife is by stepping out into their own backyard. Try it yourself. As I write this, I can look through my window at a Karoo Thrush hopping about my garden. But this post is not about the tiny garden surrounding my current apartment, but rather about my childhood home. I was tremendously fortunate to grow up on a 60 hectare farm, where  first discovered my love for nature.

Between wrapping up my PhD and starting my current lecturing position, I spent a few months of unemployment back in the house I grew up in. During that time, I discovered the thrill of recording unobtrusive nocturnal critters using a camera trap. Every afternoon, I set up the camera trap and eagerly explored the footage the following morning. It was so much fun.

After enough time, even I was amazed by the variety of species that lived on this relatively small farm. Perhaps, I should rephrase that last sentence. You see, calling it a farm is not accurate because it hasn’t been used for agricultural in more than ten years. The last cows were removed back in 2004 and since then the land was left dormant and only managed to minimise the risk of wild fire.

Still, I captured footage of 18 different mammal species, which is remarkably high for such a small area. Moreover, the camera trap is unlikely to capture any footage of bats and small rodents, so the total mammal diversity is probably even higher. I decided to write up these observations and the results have just been published online in the African Journal of Ecology. Continue reading →

How do correlations between climate and biodiversity arise? UPDATED

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Anyone who as ever watched a David Attenborough documentary knows that biodiversity differs in areas with different climates. Only a few species an survive in hot and dry deserts whereas warm and wet tropical forests are teeming with life. But have you every stopped to wonder why this is so?

Why are certain climate conditions able to support many species and others not? More specifically, how does this work mechanistically?

This was the question my co-authors and I set out to answer in our most recent paper just published online at Global Ecology and Biogeography.

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What can Sudoku teach us about ecology and evolution?

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Evolution is creeping into several different aspects of ecology. The latest buzz is all about integrating ecology and evolution. Perhaps you’ve heard of the  latest research trends in eco-evolutionary dynamics or community phylogenetics?

Theodosius Dobzhansky famously stated that “Nothing in biology makes sense except in the light of evolution“. This claim is undoubtedly true, but I’ve recently found myself wondering whether our obsession with evolution is actually clouding our ability to do good ecological research.

Please don’t misunderstand me, I am not implying that evolution is not important in explaining patterns in nature, nor am I suggesting that we should disregard evolutionary explanations for these patterns. Instead, I believe that in order to gain a deeper understanding of ecology, we should perhaps partially blind our views using “evolution blinkers”. In fact, I’d even be so bold as to claim that unless we blind ourselves to evolution, we will never be able to fully grasp the true nature of ecological processes. Unifying ecology and evolution might actual limit our ability to build ecology as a science.

Richard Feynman used a useful chess analogy to explain how physics works. I’ll borrow this style of argument to explain my stance on ecology and evolution. However, since chess is too complicated for my liking, I’ll use an even simpler game: Sudoku. Continue reading →

Long-term monitoring generally underestimates negative trends in biodiversity

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Modern conservation and environmental management rely on data. Unless you can actually show cold, hard evidence of natural deterioration, you open yourself up to criticism from denialists and other eco-skeptics. It is too easy for industry lobbyists to dismiss conservation recommendations as tree-hugger scare-mongering.

So conservationists, being the idealists that we are, decide to gather evidence for downward trends of various aspects of biodiversity. Unfortunately, efforts to quantify biodiversity trends are a major challenge. Not because measuring trends in diversity is particularly difficult, but rather because long-term monitoring is susceptible to sampling artefacts.

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The scalability of macroecology

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Russian Dolls

No matter at which scale you look at it, nature is remarkable.

Like many others, I was taught ecology in a very hierarchical way: individual organisms are part of a wider populations of species, collections of species form communities and communities come together to make up ecosystems. Similarly, single trees are nested within forests, which aggregate to form biomes. I’m sure you can come up with many comparable examples.

The trouble with such neat spatial hierarchies is that they lure us into believing that if patterns appear similar at several different spatial scales, then the processes leading to these patterns should also be similar. It’s so easy to assume that nature is like a set of Russian Dolls: each daughter exactly the same as its mother, only slightly smaller. But this is not necessarily the case.

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Species distribution modelling is not as simple as you think

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One of the most fruitful sub-fields in ecology is using climate variables to predict species’ geographic distributions. For the uninitiated, species distribution modelling assumes that species are limited in their distributions to suitable climate zones. By studying the environmental conditions where species are known to occur, you can infer the total geographic distribution by calculating the suitability of unsampled regions based on the environmental. Furthermore, using the same principle, species distribution modelling can forecast the effect of future climate change of the distribution of life on earth.

Unfortunately, studies have shown that these fancy climate-based techniques cannot consistently outperform much simpler ones based on spatial phenomena. For instance, spatial interpolation between point occurrences outperforms sophisticated climate-based predictions. Similarly, elaborate climate-based predictions perform no better than expected from random chance.

The trouble lies in the spatially-structured world we live in. Species distributions, especially at large spatial scales, are spatially-autocorrelated due to constrained dispersal. Similarly, climate variables are also spatially structured because the meteorological processes at proximal regions are generally more similar than those at distant sites.

When trying to link species distributions to climate conditions, the challenge lies is separating spatial and environmental correlations in species distributions. Specifically, we should identify three patterns in the geographical species distributions.

  • We must first identify ‘true’ correlations with the environment, which are independent of spatial patterns (E|S).
  • Next, we must identify the environmental-associations that also have a strong spatial structure (E∩S). This is known as exogenous spatial autocorrelation because it is due to autocorrelation is the underlying variables.
  • Finally, we need to identify spatial patterns that are completely independent of environmental conditions (S|E). This is called endogenous spatial autocorrelation because it supposedly stems from spatial processes, such as dispersal.

In our latest study just published online at Ecography, we set out to quantify the degree of environmental correlation, exogenous and endogenous spatial autocorrelation in the distributions of 4 423 species of amphibians, reptiles, birds and mammals in Africa. Continue reading →