Some scary stats about agriculture and biodiversity

20 07 2018

84438Last week we had the pleasure of welcoming the eminent sustainability scientist, Professor Andrew Balmford of the University of Cambridge, to our humble Ecology and Evolution Seminar Series here at Flinders University. While we couldn’t record the seminar he gave because of some of the unpublished and non-proprietary nature of some of his slides, I thought it would be interesting, useful, and thought-provoking to summarise some of the information he gave.

Andrew started off by telling us some of the environmental implications of farming worldwide. Today, existing agriculture covers more than half of ‘useable’ land (i.e., excluding unproductive deserts, etc.), and it has doubled nitrogen fixation rates from a pre-industrial baseline. Globally, agriculture is responsible for between 19 and 35% of all greenhouse gas emissions, and it has caused approximately 40% increase in observed sea-level rise (1961-2003). Not surprisingly, agriculture already occupies the regions of highest biodiversity globally, and is subsequently the greatest source of threat to species.

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Having more tree species makes us wealthier

28 01 2013

money treeAs more and more empirical evidence pours in from all corners of the globe, we can only draw one conclusion about the crude measure of species richness (i.e., number of species) – having more species around makes us richer.

And I’m not talking about the esoteric or ‘spiritual’ richness that the hippies dribble about around the campfire after a few dozen cones pulled off the bong (I’ll let the confused among you try to work the meaning of that one out by yourselves), I’m talking about real money (incorporated into my concept of ‘biowealth‘).

The idea that ‘more is better’ in terms of the number of species has traditionally found some (at times, conflicting) empirical support in the plant ecology literature, the latest evidence about which I wrote last year. This, the so-called ‘diversity-productivity’ relationship (DPR), demonstrates that as a forest or grass ecosystem gains more species, its average or total biomass production increases.

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No-extinction targets are destined to fail

21 09 2012

I’ve been meaning to write about this for a while, and now finally I have been given the opportunity to put my ideas ‘down on paper’ (seems like a bit of an old-fashioned expression these days). Now this post might strike some as overly parochial because it concerns the state in which I live, but the concept applies to every jurisdiction that passes laws designed to protect biodiversity. So please look beyond my navel and place the example within your own specific context.

As CB readers will appreciate, I am firmly in support of the application of conservation triage – that is, the intelligent, objective and realistic way of attributing finite resources to minimise extinctions for the greatest number of (‘important’) species. Note that deciding which species are ‘important’ is the only fly in the unguent here, with ‘importance’ being defined inter alia as having a large range (to encompass many other species simultaneously), having an important ecological function or ecosystem service, representing rare genotypes, or being iconic (such that people become interested in investing to offset extinction.

But without getting into the specifics of triage per se, a related issue is how we set environmental policy targets. While it’s a lovely, utopian pipe dream that somehow our consumptive 7-billion-and-growing human population will somehow retract its massive ecological footprint and be able to save all species from extinction, we all know that this is irrevocably  fantastical.

So when legislation is passed that is clearly unattainable, why do we accept it as realistic? My case in point is South Australia’s ‘No Species Loss Strategy‘ (you can download the entire 7.3 Mb document here) that aims to

“…lose no more species in South Australia, whether they be on land, in rivers, creeks, lakes and estuaries or in the sea.”

When I first learned of the Strategy, I instantly thought to myself that while the aims are laudable, and many of the actions proposed are good ones, the entire policy is rendered toothless by the small issue of being impossible. Read the rest of this entry »





Ghost extinctions

5 07 2012

The Philippine bare-backed fruit bat (Dobsonia chapmani; body size = < 220 mm, < 150 g; IUCN status: ‘Critically Endangered A2cd’) is endemic to lowland rain forests [top habitat image] from Negros and Cebu islands. This species of flying fox had been missing from the 1970s and was declared extinct in 2002 (34). In May 2003, five specimens [one shown in the picture above] were trapped in night nets in the Calatong forest (Negros Island), a ~ 1,000-ha fragment of secondary rain forest and agricultural lands [bottom habitat image] (35). The species is reliant on fruit-bearing vegetation and caves for feeding and roosting, respectively. As with many other Philippine bats, it suffers from habitat degradation and hunting. The family Pteropodidae comprises > 150 species. Despite their Draculian look, they all feed on fruits and nectar, and act as important plant pollinators (36), as well as disease vectors such as Ebola virus (37). Flying foxes are distributed in the tropics and subtropics from the Eastern Mediterranean, through the Arabian Peninsula, Asia, Australia, and many islands of the Indian Ocean. Photos courtesy of Ely L. Alcala.

Jared Diamond (1) coined the expression ‘evil quartet’ for the four main human causes of species extinctions: habitat loss/fragmentation, overkill, introduced species and extinction chains [with climate change and extinction synergies (2), the updated expression would be ‘evil sextet”]. However, one third of ‘extinct’ mammal species has been ‘found’ again. Recent studies reveal that the probability of rediscovery depends on the cause of extinction.

Arriving in a city to search for an old friend, I would first look in the suburb where he lived, the pub where we enjoyed a drink and some music, or the park where we used to play football. But if my friend was an outlaw, or had recently gone through a traumatic experience, my chances of finding him at his favourite spots would shrink.

If, instead of a friend, we are searching for the last survivors of an extinct-declared species, surveys also tend to take place in the habitat in which the species was previously found. Such a strategy rests on the classical hypothesis that, given the spatial distribution of a species, its gradual decline must occur from the periphery to the core of its distribution (‘range collapse’) where, in theory, the habitat should be of better quality and the number of individuals higher (3). In contrast, recent work supports that the trajectory of demise of threatened vertebrates progresses from the core to the periphery (‘range eclipse’) (4), because many perturbations make their way as a progressive wave, e.g, fire, logging or urbanisation.

Diana Fisher (5) supports the ‘range eclipse’ hypothesis for ‘extinct’ mammals which have been rediscovered. She quantifies that 60% of the new records are made from peripheral habitats, mainly when the principal cause of extirpation is habitat loss. Not only that, on average species are rediscovered at altitudes 35 % higher than historical records, and only in 5 % of the cases at the locality where it had been last seen.

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Different is better

6 03 2012

I found a nice complement to my More is Better post from January where I reported the results of a new meta-analysis demonstrating how higher species evenness and diversity engendered greater forest productivity – great empirical evidence for the so-called diversity-productivity relationship.

The latest paper adding convincing evidence regarding the important role of species diversity in maintaining ecosystem function comes from Marc Cadotte and colleagues published online early in Ecology. The paper, Phylogenetic diversity promotes ecosystem stability, looks at the problem from a slightly different angle.

If you recall from Zhang and colleagues, forest plots composed of many different species were more productive than single-species stands, and more ‘even’ (i.e., a metric which includes relative abundance of each species in system) stands were more productive, and better at explaining the variance in productivity than species richness alone.

Of course, species richness is considered only a blunt instrument to measure ‘biodiversity’, with evenness providing only a slight improvement. Ideally, we should be talking about genetic diversity considering this is the fundamental unit on which most of evolutionary processes operate (i.e., genes and gene complexes).

So Cadotte and colleagues measured genetic diversity within experimental plots of grassland savanna species established in Minnesota, USA (i.e., consisting of C3 grasses, C4 grasses, legumes, non-legume herbaceous forbs and two woody species) and compared this to ecosystem ‘stability’ (i.e., above-ground biomass divided by inter-annual standard deviation). They measured genetic diversity using four different metrics:

  1. the sum of the phylogenetic branch lengths represented by a set of co-occurring species
  2. the mean nearest taxon distance = the average of the shortest phylogenetic distance for each species to its closest relative
  3. the mean pairwise distance = the average of all phylogenetic distances connecting species in the sample; and
  4. an entropic measure based on the relative distribution of evolutionary distinctiveness, measured as the amount of a species’ evolutionary history that is not shared with other species Read the rest of this entry »




S.A.F.E. = Species Ability to Forestall Extinction

8 01 2011

Note: I’ve just rehashed this post (30/03/2011) because the paper is now available online (see comment stream). Stay tuned for the media release next week. – CJAB

I’ve been more or less underground for the last 3 weeks. It has been a wonderful break (mostly) from the normally hectic pace of academic life. Thanks for all those who remain despite the recent silence.

© Ezprezzo.com

But I’m back now with a post about a paper we’ve just had accepted in Frontiers in Ecology and Environment. In my opinion it’s a leap forward in how we measure relative threat risk among species, despite some criticism.

I’ve written in past posts about the ‘magic’ minimum number of individuals that should be in a population to reduce the chance of extinction from random events. The so-called ‘minimum viable population (MVP) size’ is basically the abundance of a (connected) population below which random events take over from factors causing sustained declines (Caughley’s distinction between the ‘declining’ and ‘small’ population paradigms).

Up until the last few years, the MVP size was considered to be a population- or species-specific value, and it required very detailed demographic, genetic and biogeographical data to estimate – not something that biologists tend to have at their fingertips for most high-risk species. However, several papers published by our group (Minimum viable population size and global extinction risk are unrelated, Minimum viable population size: a meta-analysis of 30 years of published estimates and Pragmatic population viability targets in a rapidly changing world) have shown that there is in fact little variation in this number among the best-studied species; both demographic and genetic data support a number of around 5000 to avoid crossing the deadly threshold.

Now the fourth paper in this series has just been accepted (sorry, no link yet, but I’ll let you all know as soon as it is available), and it was organised and led by Reuben Clements, and co-written by me, Barry Brook and Bill Laurance.

The idea is fairly simple and it somewhat amazes me that it hasn’t been implemented before. The SAFE (Species Ability to Forestall Extinction) index is simply the distance a population is (in terms of abundance) from its MVP. In the absence of a species-specific value, we used the 5000-individual threshold. Thus, Read the rest of this entry »





How many species are there?

4 06 2010

© japanprobe.com

An interesting research note just came out in the American Naturalist by Hamilton and colleagues entitled Quantifying uncertainty in estimation of tropical arthropod species richness. I retweeted a Science Daily twitter feed on this that had a terribly misleading opening line: “New calculations reveal that the number of species on Earth is likely to be in the order of several million rather than tens of millions“. This is, of course, absolute rubbish because the authors only looked at estimating tropical arthropod richness, not all species on Earth. The number of protists alone is probably > 4 million species, and there are an estimated > 1.5 fungi.

That whinge about crap reporting aside, this is what Hamilton and colleagues concluded:

  • using stochastic models, they predict medians of 3.7 million and 2.5 million tropical arthropod species globally
  • estimates of 30 million species or greater are predicted to have < 0.00001 probability
  • uncertainty in the proportion of canopy arthropod species that are beetles is the most influential parameter
  • in spite of 250 years of taxonomy and around 855000 species of arthropods already described, approximately 70 % await description

Interesting, but I didn’t give it much notice until New Scientist contacted me to get an assessment (their article will appear shortly). This is what I had to say: Read the rest of this entry »