Natural communities are exposed to a multitude of environmental events, such as fires, droughts and floods. These events cause random changes in environmental variables such as temperature and rainfall, which in turn shape the dynamics of species abundances and hence patterns of biodiversity. A common feature of time-series of environmental variables is that they are positively correlated over time. As a result, variables change more slowly than they would under zero correlation, and fluctuations of lower frequency have greater influence. In technical terms, this corresponds to “reddened” environmental noise, analogous to red light waves having relatively low frequencies, whereas the uncorrelated case corresponds to white noise. Previous ecological modelling studies have focussed mostly only on white noise rather than reddened noise.

In a new study recently published in the Journal of Mathematical Biology, we address this knowledge gap by constructing a new stochastic community model with reddened environmental noise, and then mathematically analysing the model to show how this type of noise changes the distribution of individuals among species. We find that redder noise (with greater correlation in time) helps to increase the expected number of species with higher abundances, by prolonging periods where the environment has a positive effect on species’ growth rates. This results in a flatter distribution of species across abundance classes compared with the white noise case. Overall, our findings highlight the importance of incorporating coloured noise when using models to predict patterns of biodiversity.

Fung, T., J. P. O’Dwyer, & R. A. Chisholm. Species-abundance distributions under colored environmental noise. Journal of Mathematical Biology (in press)

Species-abundance distributions from the new model under different colored environmental noise regimes

The recent peat fires in Southeast Asia were an environmental disaster. But many uncertainties remain about the extent and impact of the fires. One is exactly how much carbon was emitted. The media have reported that carbon emissions from this one event were higher than annual emissions from Germany or the US. But how certain are such estimates?

Lahiru’s letter to Global Change Biology cautions against jumping to conclusions about the impacts of the peat fires without proper quantitative analyses. He suggests we not be alarmist and instead take a step back to do the science.

Wijedasa, L. S., Peat soil bulk density important for estimation of peatland fire emissions,
Global Change Biology (in press)

http://onlinelibrary.wiley.com/doi/10.1111/gcb.13364/abstract?campaign=wolacceptedarticle

Catharina is back in Borneo for another field season and recently went to the 5th International Bornean Frog Race, held in Sarawak and organised by Dr Indraneil Das from the University of Malaysia Sarawak (UNIMAS). The event aims to generate interest in amphibians and features multiple talks and workshops. The race itself involves participants spending two hours searching for frogs in the field, with prizes awarded for categories such as best photo and most species found. Robin Moore was the invited guest speaker for the event this year and Catharina had the privilege of being allowed to accompany him and the UNIMAS team to look for the very rare Bornean Rainbow Toad (Ansonia latidisca) a few nights later.

In a new paper just published in Proceedings of the Royal Society B, we solve a classic ecological conundrum posed 50 years ago: the small-island effect. MacArthur and Wilson’s classic theory of island biogeography predicts that the number of species on an island should be positively related to island area. This prediction is generally borne out by data, but it is violated for small islands, where there is no apparent relationship between island area and species richness. In the new paper, we explain this “small-island effect” as arising from a niche-structured regime that prevails when immigration is very low—a situation commonly found on small islands. We verify our theory by showing that a corresponding mathematical model gives excellent fits to 100 archipelago data sets from around the world, and by confirming key predictions about when the small-island effect should be more prominent.

Chisholm, R. A., T. Fung, D. Chimalakonda, J. P. O’Dwyer (2016). Maintenance of biodiversity on islands. Proceedings of the Royal Society B

The Honours students have submitted their theses. Jasline investigated the rate of accumulation of knowledge of global mammal diversity over the last three centuries, focussing specifically on a comparison of known phylogenetic diversity versus known species diversity. Alicia studied the rate of extinction of mammal species in Singapore in recent centuries, with a focus on estimating undetected extinctions. Lin Yuan estimated Singaporeans’ willingness to pay for haze mitigation using surveys of the public both in person and online. Yi Zhen conducted surveys in nature reserves in Singapore to explore factors affecting people’s appreciation of the quality of nature reserves. Yin Yue modelled stray dog populations in Nepal to explore optimal strategies for dog sterilisation and population control. Congratulations to all for a job well done!

Deepthi recently finished her first season of field work in the agrarian landscapes of Peninsular India where she documented water bird diversity in 58 human-made wetlands. Using point count surveys, she recorded about 45,000 individuals of 78 species over three visits to each wetland.

She will use these data to estimate detection probabilities and abundances of the species and to understand patch and landscape correlates of water bird diversity.  She then plans to build patch-occupancy models to investigate questions pertaining to metapopulation dynamics and persistence.

Quanta magazine has written a popular article focussing on our recent environmental variance paper:
https://www.quantamagazine.org/20160311-a-timely-fix-for-a-grand-theory-of-nature/

The article has also been syndicated in The Atlantic.

Strong environmental forcings, from storms to fires and insect outbreaks to elephants, drive tree population dynamics in forests across the world. Despite the pervasiveness of these environmental drivers, most theoretical models of forest tree dynamics ignore them, focussing instead on neutral drift and niche stabilisation. What effect does environmental variance have on patterns of forest diversity? In our new paper, in press at Ecology, we show that a model with realistically strong environmental forcings can accurately reproduce both static and dynamic patterns of diversity in two tropical forest plots, one in Malaysia and one in Panama. This is superior to previous similar models that are unable to capture both types of diversity simultaneously—for example, neutral models are only able to realistically produce static patterns such as species-abundance distributions. Our work further underscores the need to include strong components of environmental variance in realistic models of tropical forest dynamics.

This work was led by Tak Fung, with Kassim Abd. Rahman and Christine Fletcher (Forest Research Institute Malaysia), and James O’Dwyer (Univ. of Illinois) as a collaborators.

Reproducing static and dynamic biodiversity patterns in tropical forests: the critical role of environmental variance. Tak Fung, James P. O’Dwyer, Kassim Abd. Rahman, Christine D. Fletcher and Ryan A. Chisholm, in press, Ecology.

Poulsenia armata, a tree that was formerly dominant in the canopy at the Panama plot but suffered 50% mortality during a 1980s drought (image credit: biogeodb.stri.si.edu).

A new article on Mongabay discusses the potential for drones and other automated technologies to be used for forest restoration. It covers recent developments in the field of automated forest restoration, including last year’s Chiang Mai workshop and our forest drone trials.

Forest restoration: from Stone Age to drone age

Forest restoration: from Stone Age to drone age

Photo by S. Elliott

Ryan has just returned from France, where he gave a series of guest lectures and workshops to the Erasmus Mundus International Master in Applied Ecology programme at the University of Poitiers. This Masters programme draws in students from all around the world and allows students to rotate between different countries in the European Union over two years.

Ryan also visited and presented seminars at Jerome Chave’s lab at the University of Toulouse and at the Station for Theoretical and Experimental Ecology in Moulis, nestled in the foothills of the Pyrenees.