new paper

Forests feed lake life

Our latest paper has just appeared in Science Advances.  In it, we present widespread evidence that aquatic consumers use terrestrial resources depending on the features of surrounding catchments.  It is really nice to see this out as it caps the food web workshop we organised in Cambridge more than two years ago and includes data we collected during our summer 2014 field campaign.  There’s a nice write up of the work put out by our friends at the Cary Institute.

The work emerged out of our forest fuel fish growth story, which hinted that there can be a lot of variation in the extent to which lake food webs use terrestrially derived material, depending on the features of the surrounding catchments.  With funding from a NERC collaborative grant, our new paper managed to assemble the largest dataset to date of the isotopic composition of zooplankton and their associated food webs from across 147 lakes spanning the boreal to subtropics.  Our aim was to address the use of terrestrial resource in lake food webs once and for all.

Algae and land plants differ in their assimilation of heavy versus light forms of atoms such as carbon, allowing the ratios between these two forms to be used as dietary tracers.  Using these isotopic signatures, we discovered that half of all the zooplankton samples we amassed were comprised of at least 42% terrestrially derived material, but this was underpinned by large variation ranging from 11 to 83%.  Using some awfully complex stats, we go on to show that terrestrial support of zooplankton was generally greatest in lakes with long shorelines and surrounded by dense vegetation and rich soils.  This work now explains the large variation in terrestrial resource use by aquatic food webs and delivers a major advance towards resolving the ‘controversy’ around this process.

Rewinding the Tape of Life

Journal of Ecology Blog

If evolution happened anew, what would the present-day plant world look like?  That is, would the randomized processes that govern evolutionary change tell a different story? And particularly for plants which are sessile organisms, is the starting point of ‘who gets there first’ the most important of all?

Priority effects – the order and timing of species arrival into local communities – can affect ecological community structure and functioning, with profound effects for species persistence and ecological interactions (Chase et al., 2000; van de Voorde et al., 2011). As such, the arrival of different species at different times can dramatically alter the evolutionary tapestry of any given system on ecological time frames, but also in evolutionary time. In particular, the diversification of early arriving species can pre-empt available niche space to prevent the establishment, dominance or diversification of species that arrive later on down the road.

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Making sense of canopies

Béatrice Wedeux and David Coomes published a paper in Biogeosciences analysing how environmental factors and selective logging interact to shape the canopies of tropical forests. Using airborne laser scanning technology across a 750 km2peat swamp forest landscape in Borneo, the study reveals strong shifts in canopy height and gap patterns along environmental gradients linked to changing peat depth. In areas where logging roads were detected on historical satellite imagery, the canopy is lowered and has larger gaps, especially so on deep peat where tree growth is thought to be limited by low nutrient availability and waterlogging. The study identifies a close link between the height and the gap structure of tropical peat swamp forests at the landscape scale and reinforces the vulnerability of this ecosystem to human disturbance. The degradation of tropical peat swamps has been at the heart of climate negotiations in Paris, as emissions from fires in Indonesian peatlands over the last couple of months – exacerbated by a dry El Niño spell – approach the total annual emissions of Brazil (1.62 billion metric tons;


Airborne laser scanning allows the detection of openings at different height cross-sections of the canopies of old-growth and selectively logged forests.

Read online: Wedeux, BMM and Coomes DA (2015) Landscape-scale changes in forest canopy structure across a partially logged tropical peat swamp, BIOGEOSCIENCES 12(22):6707–6719, DOI: 10.5194/bg-12-6707-2015.

The future of environmentally-friendly farming?

Our first paper on the agri-environment has just appeared in this month’s issue of PLoS Biology.  This is an important piece for us as it provides a foundation for empirical work being carried out by several group members.

The paper essentially makes three main points.  The first is that we spend a lot more money subsidizing farming than trying to mitigate its environmental impacts.  We’ve tried to plot this out below.  What you can clearly see is that the purple (mitigation expenditure) is nearly invisible relative to what is spent on subsidizing farming (shown in the orange slices).

Financial support to farmers from taxpayers and consumers associated with agricultural policies as a proportion of the total value of agricultural production (VoP) at the farm gate.

The figure now provides what is essentially a map of the ‘perversity‘ of agricultural subsidies – showing where we spend money to do things that are often bad for the environment and costly to the economy.  A first step in reducing conflict between agriculture and the natural environment would be to do away with the subsidies in orange.

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Explaining the origins of species diversity

The July 2015 issue of New Phytologist has come out and its a doozy!  The entire issue features work on evolutionary plant radiations, drawing together a range of papers that summarize the current state of knowledge about “where, when, why, and how” plant radiations happened.  An editorial by Colin Hughes, Reto Nyffeler Peter Linder outlines the content of what will surely be a landmark issue for years to come!

Many, if not all, of these papers were presented at a symposium organized in Zurich that we attended with our New Zealand collaborators Professors Bill and Daphne Lee in June 2014:

We're somewhere in the crowd

We’re somewhere in the crowd …

For me, this was possibly one of the most intellectually stimulating meetings that I’ve ever attended.  Talks drew major figures in plant ecology, evolution, and systematics and really pushed the boundaries out on ‘diversification’ research.  The field itself is still arguably quite new, with many of the key questions synthesized in a 2008 paper by Peter Linder.  In fact, we have a PhD studentship available to follow-up some of these questions and build on what we talked about at the meeting.

You might have noticed that we even have a contribution in the New Phytologist Special Issue.  Our paper tests the mechanisms by which plant evolutionary radiations emerge and influence ecological dynamics.  We apply more of our expertise in structural equation modelling to focus on 16 species-rich genera in the alpine zone of New Zealand.

Diversity in New Zealand’s alpine.  Celmisia, Chionochloa, Dracophyllum, and Veronica all appear in this photo.

One of the most exciting aspects of our paper is that we’ve tried to reconstruct the niche space that each genus has occupied over the last 20 million years.  This is fairly ambitious and has involved tasks like reconstructing sea surface temperatures through the Cenozoic from isotopic measurements of foraminifera deposited in marine sediment cores, and then using these to estimate past land temperatures.  We’ve also had to consider that the alpine zone has grown immensely over time with uplift of the Southern Alps.  To do so, we collated radiometric dates of rocks and tried to infer their rate of uplift since the Miocene.

Overall, our results suggest that genera that colonized New Zealand earlier encountered more ‘vacant’ environmental space, which promoted species diversification and further occupancy of the environment.  Genera that occupied more environmental space were subsequently more dominant in present-day vegetation plots.  The key message is that time not only explains why diversity arises, but how this diversity influences ecological dynamics.  The Special Issue has many other fabulous papers, so do check it out!

Mutualisms – a little help from friends?

It’s been a while since we’ve last blogged but we’re hoping to pick it up more regularly again over the next few months now that the group is quickly growing.

For now, I thought I’d comment on an interesting study published this month in Applied Vegetation Science by Laura Burkle and Travis Belote.  It links up nicely to work we’re doing on priority effects, which is the idea that species that arrive earlier into a habitat influence the interspecific interactions of later arriving colonists.  Priority effects are hardly surprising. Succession theory long predicted that communities develop along different trajectories depending on the species that are initially present.  But generalizing the direction and strength of priority effects remains challenging.  This is where Sgt. Pepper’s Lonely Hearts Club Band can offer some advice:

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Lakes turning to jelly

Our latest paper in the Proceedings of the Royal Society on the “jellification” of temperate lakes has gotten an impressive amount of on-line attention.  At the time of writing this blog, Altmetric scores it as the 22nd highest ranking paper ever published in the journal.  You can read summaries from the Washington Post, New York Times, Daily Mail, CBC, CBC Radio, and Yahoo, among others.  I’ve also done four separate interviews this week with BBC radio stations (BBC Radio 5, BBC Wales, BBC Cambridgeshire).  You can catch the latest, with the BBC World Service from the 26th of Nov, below:


The main finding of the paper is that a small planktonic animal named Holopedium glacialis has been dramatically increasing in two very different lake regions of Canada as the keystone grazer in these lakes, the water flea (Daphnia spp.), has been disappearing.  Our results show that this is mainly driven by declines in lake water [Ca].  Daphnia need large amounts of Ca to build their body shell, while Holopedium surround themselves in a gelatinous polysaccharide “bubble”:

An individual Holopedium with the jelly capsule clearly visible. (Photo: Ian Gardiner / E-Fauna BC)

This jelly also protects Holopedium from predators.  By contrast, Daphnia are increasingly susceptible to predators at low [Ca] because their ability to induce evolved defences is also impaired. Our analyses show how vanishing Daphnia have now left more algae uneaten for their competitors to exploit, allowing them to multiply in number.  Many media reports have picked up on this as Holopedium liking ‘pollution’, with low [Ca] somehow being the result of this.  But it is more in fact a legacy of pollution.  While we have curbed industrial emissions and reduced acid rain, the historical depletion of base cations from the thin soils of the boreal shield, have left behind much lower [Ca] than present prior to industrial activity.  Ca concentrations have consequently been falling across much of North America and Europe.

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Climate change and the fate of New Zealand’s forests

By storing carbon in wood, forests currently play a key role in mitigating climate change. However, there is growing concern that as climate changes forests could shift from being a net carbon sink to a source. In our recent paper published in Global Change Biology we explore the consequences of climate change on wood production in New Zealand’s forests.

Using repeat census data from 1070 permanent forests plots, we looked at how wood production changes over temperature and rainfall gradient across New Zealand, and then use this information to predict how climate change will affect forest carbon dynamics in the near future. We find that climate influences wood production both directly, by driving physiological responses at the tree level, and indirectly, by determining the composition and structure of forests. If the composition and structure of New Zealand’s forests were to remain unchanged over the next 30 years, then wood production would increase by 6–23%, primarily as a result of physiological responses to warmer temperatures. However, if warmth-demanding trees were able to migrate into currently cooler areas and if denser canopies were able to form, then a different response is likely: forests growing in the cool mountain environments would show a 30% increase in wood production, while those in the lowland would hardly respond. We conclude that response of wood production to anthropogenic climate change is not only dependent on the physiological responses of individual trees, but is highly contingent on whether forests adjust in composition and structure.

Wood production in mixed species forests

Our latest paper aiming to untangle the mechanisms behind diversity-productivity relationships in forests has just been published in Journal of Ecology. Working in Mediterranean mixed forests in Spain, we find that complementary use of canopy space by oak and pine species means that mixtures of these two functional groups produce around 50% more wood each year compared to monocultures. However, the magnitude of the diversity effect on wood production fluctuates over time, decreasing noticeably in strength during drought years.

Tree cores of pine and oak species collected in the Alto Tajo Natural Park, Spain.

Tree cores of pine and oak species collected in the Alto Tajo Natural Park, Spain.

The study was conducted in the Alto Tajo Natural Park, in the Guadalajara province of central Spain, as part of the FunDivEUROPE project which aims to determine the functional significance of forest biodiversity. Using tree ring data from permanent forest plots we explored how mixing pine (Pinus sylvestris and Pinus nigra) and oak species (Quercus faginea and Quercus ilex) influences wood production in Iberian forests. We found that pine species receive more light, develop larger crowns and grow 138–155% faster when in mixture with oaks. However, this positive effect of species mixing on growth was severely reduced under drought conditions due to increased competition for water with neighbouring oaks. In contrast to pines, oak trees were less responsive to mixing, primarily as a result of their ability to tolerate shade and water shortage. Our results suggest that competition for light is key in driving positive diversity effects in forests, but also show that the strength of complementarity can change in response to climatic conditions.

A view of the Tajo river cutting through the valley below on its way to Lisbon.

A view of the Tajo river cutting through the valley below on its way to Lisbon.

More ways of living on a bush than on a bluebell

Some years ago, a fascinating article in the National Geographic described the exceptional diversity of bat species to be found in Barro Colorado Island, Panama – incidentally where Ed Tanner is currently with some of his PhD students. Research by the Smithsonian Tropical Research Institute and others had described 74 species, which managed to coexist by carving out distinct, often ingenious, niches. Some bats are physically adapted to hunt in open spaces, others in gaps and along edges, still others in the fine interstitial spaces of lower understorey layers. It is a dramatic example of how habitat structural complexity is related to, and helps promote, species richness.

We explore this relationship between habitat structure and species richness, and its relevance, in an article recently published in Methods in Ecology and Evolution. Building on an earlier review (Tews et al 2004, J. Biogeog 31:79-92) through an analysis of 199 papers published 2004-2013, we find that a positive relationship between habitat complexity or heterogeneity and animal species richness or diversity is found in over 75% of investigated cases, across different taxonomic groups and ecosystem types. It seems that Lawton (1978) was right when he observed: “There are more ways of living on a bush than on a bluebell”. Given this common pattern, and building on Coomes Group’s developing experience of using airborne lidar to study forests, we argue that this powerful vertical-profiling tool could be used to deliver habitat structural indicators of species richness over large spatial extents. More spatially and temporally precise information on species richness and habitat quality is increasingly important in responding to the unceasing loss of biodiversity across the planet, so we hope the article might contribute to developing new tools to meet this challenge.