Maths experts question key ecological theory

June 20, 2012

Mathematicians at the University of York in the UK and the University of Canterbury in New Zealand say they have disproved a widely accepted theory underpinning the operation of complex networks of interactions in the natural world.

Networks are a powerful way to describe ecological communities, which typically involve large numbers of species that can exhibit both negative (e.g. competition or predation) and positive (e.g. mutualism) interactions with one another. Recent mathematical and computational analysis suggested that nestedness -- the tendency for ecological specialists to interact with a subset of the species that also interact with more generalist species -- increases species richness.

But the researchers from the York Centre for Complex Systems Analysis (YCCSA) and the Biomathematics Research Centre at Canterbury say they have proved the reverse is true, using mathematical models based on plant-pollinator networks observed in the wild. The data span the globe, ranging from tropical rainforests to the high Arctic, and include species such as birds of paradise and hummingbirds as well as insect pollinators such as bees, wasps and butterflies.

The research is published in the latest edition of Nature.

By carefully examining previous analytic results, and applying computational and statistical methods to 59 empirical datasets representing mutualistic plant-pollinator networks, they say they disprove the accepted theory of nestedness. Instead, they contend that the number of mutualistic partners a species has is a much better predictor of individual species survival and community persistence.

Co-author Dr Jon Pitchford, who is also a member of the Departments of Biology and Mathematics at York, said: "We know that real mutualistic communities are nested -- they have sets of interactions-within-interactions, rather like Russian dolls. We are trying to understand how this is related to their biodiversity and stability. This will enable us to better understand the way ecological networks are affected by environmental fluctuation and climate change."

Co-author Dr Alex James, of the Department of Mathematics and Statistics at Canterbury, said: "It is a well-used phrase but correlation does not imply causation. Although a cursory glance at real networks can make it appear that nestedness is correlated with survival, you need to delve deeper to realise this is a secondary correlation. The stronger and more causal relationship is between the number of mutualistic partners a species has and its survival."

Co-author Dr Michael Plank, also of the Department of Mathematics and Statistics at Canterbury, added: "Real-life networks, whether they are from ecology, economics, or Facebook, can be large and complex. This makes it difficult to tease apart causal relationships from confounding factors. This is where mathematical models come into their own. They allow us to systematically change one network attribute, such as nestedness, whilst controlling for other variables."
The researchers were supported by the RSNZ Marsden Fund and Dr Pitchford was supported by the University of Canterbury Erskine Programme.

University of York

Related Biodiversity Articles from Brightsurf:

Biodiversity hypothesis called into question
How can we explain the fact that no single species predominates?

Using the past to maintain future biodiversity
New research shows that safeguarding species and ecosystems and the benefits they provide for society against future climatic change requires effective solutions which can only be formulated from reliable forecasts.

Changes in farming urgent to rescue biodiversity
Humans depend on farming for their survival but this activity takes up more than one-third of the world's landmass and endangers 62% of all threatened species.

Predicting the biodiversity of rivers
Biodiversity and thus the state of river ecosystems can now be predicted by combining environmental DNA with hydrological methods, researchers from the University of Zurich and Eawag have found.

About the distribution of biodiversity on our planet
Large open-water fish predators such as tunas or sharks hunt for prey more intensively in the temperate zone than near the equator.

Bargain-hunting for biodiversity
The best bargains for conserving some of the world's most vulnerable salamanders and other vertebrate species can be found in Central Texas and the Appalachians, according to new conservation tools developed at the National Institute for Mathematical and Biological Synthesis (NIMBioS) at the University of Tennessee, Knoxville.

Researchers solve old biodiversity mystery
The underlying cause for why some regions are home to an extremely large number of animal species may be found in the evolutionary adaptations of species, and how they limit their dispersion to specific natural habitats.

Biodiversity offsetting is contentious -- here's an alternative
A new approach to compensate for the impact of development may be an effective alternative to biodiversity offsetting -- and help nations achieve international biodiversity targets.

Biodiversity yields financial returns
Farmers could increase their revenues by increasing biodiversity on their land.

Biodiversity and wind energy
The location and operation of wind energy plants are often in direct conflict with the legal protection of endangered species.

Read More: Biodiversity News and Biodiversity Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to