Lecture 18 - Biodiversity and ecosystem functioning
An area of research which was found on biodiversity loss and extinction from last couple
Mass extinction and biodiversity loss
Extinction is a reality for our entire generation. Why should we care? Because biodiversity
is highly linked to human well being. This is called biodiversity and ecosystem functioning.
Whats the big deal about extinction?
Since it is part of the circle of life. We know that there have been at least five major
extinctions with the last one being the dinosaurs 65 million years ago. We can see the rates
of extinction from the past and see what the rates should be now but we find that the rates
of extinction is going up now from what it was millions of years ago.
Every line on graph is ten fold increase of extinction rate.
This is due to humans.
What are the threats to biodiversity?
Toxins, invasive species, overexploitation, disease spread, climate change, etc.
What is an ecosystem function?
Chemical and biological processes or attributes that contribute to the self-maintenance of
Ecosystem function examples:
• Carbon cycling
• Provision of habitat
• Nutrient cycling (e.g. N, P)
Ecosystem services are the benefits that humans get from environment
Benefits people obtain from ecosystems, including provisioning services, regulating
services, cultural services, and supporting services.
Examples of Ecosystem services:
• Water filtration
• Pollution filtration
• Buffering from natural disasters
• Food production
• Wood production
• Erosion control
• Climate regulation
• Waste decomposition
• Provision of pharmaceuticals
Biodiversity and Ecosystem Function:
The link was not that clear... Two experiments do prove this...
Two new experiments -1994: Tilman and John Downing, “Biodiversity and stability in grasslands”
– Shahid Naeem et al., Nature “Declining biodiversity can alter the performance of
Cedar Creek Ecosystem Science Reserve, MN, USA –Tilman and Downing
Tilman and Downing was done in Minnesota and they took a field and divided into mini
ecosystems with different number of species
Ecotron, Silwood Park, UK – Naeem et al.
Naeem took even smaller ecosystems in pots and grew them in ecotrons which controls for
environmental and climate factors
The experiment of Tilman then went through a drought and so they worked with the new
environment and found that the more species found in the ecosystem, the more chance that
they survived and were stable during the drought.
Naeem they had levels of biodiversity and they focused on productivity. This was new thing that was never tested in ecology before.
Meanwhile, somewhere in the mountains of Tennessee…
-1997: Michael Huston claims that there are “Hidden treatments in ecological experiments”
Michael Huston - said that these studies missed the selection factor which is a statistical
issue. The black star is the power house species and all the rest are the same. In the Naeem
and Tilman experiments, they just randomly choose species and planted them together.
They choose from a set (species pool) to make plots (samples). When you only choose two
species, there is not a high chance that you include the black star species which is driving
all the functioning of the entire ecosystem. However, as you increase the number of species
(diversity in the ecosystem) there is a higher chance that you will include the black star
that is driving all the function of that ecosystem.
Naeem and Tilman said that it is due to the Complementarity Effects Think about a sample with only one species – called a monoculture. All individuals of the
plot are about the same size and same roots if all of them are the same species. This means
that they are all competing for the same set of limited resources. If different species
(diverse with many different species) they partition the resources then they use different
resources so much more of the available resource are used so there is more productivity.
So now they try to solv