Lecture 1 Notes

Seite 1

Brief history of migration

-Pre 5000 years ago Europe was covered in ice up to the Pyranees, Alps, Balkan mountains.

-These mountain ranges created a barrier. Most biodiversity (seed sources) were South of these barriers.

-When the ice retreated, these seed sources expanded.

-Primary refugium (worked out from either DNA studies or pollen studies) show how Oaks spread up from the med after the last ice age retreated.

-Palynology, study of pollen. Pollen contains spiropollanin? Which is very robust and good for studies. These are found using cores from the ground.

-OR we can use genetic markers. Mitchondrial DNA is highly conserved because it is only maternaly recieved and not recombined with paternal DNA. It has a fairly steady mutation rate which allows use to measure how far apart species are in time. In plants we use chloroplasts too?

-Migration rate ranges enormously (25-2000m per year) depending on species. This shows how different species will react to climate change.

- Some species have not migrated as far as they could. This could be due to climate, topography as well as dispersal tactics.

-Tree biodiversity in Europe is still the highest in the med. Conifers have stuck to more mountainous areas, broadleaves have spread more.

-Challenging, difficult climates tend to limit dispersal and therefore diversity, see boreal forests in Scandanvia.

Ecosystem theory

-Ecosystem definitions from Weiss and Bahg

-They have emergent properties (greater than the sum of its parts)

-Self regulating

- Has 4 key terms; Constancy - how much things change in an ecosystem. Resistance - how hard something is to break. Resiliance - how fast something bounces back. Persistance - how long a system lasts

- Graphical representations of resilience and resistance. Shows tipping points

- Over one tipping point, leads to a regime shift.

-Identifying tipping points can be very difficult in real life.

Case study - 'Cloud Forests'

- Main thing is it intercepts water in tropics

-If you cut it down it stops intercepting water

- Everything then dries out and its impossible to get the forest back

Effects of Biodiversity

-Different species have different functional properties

-It is hard to say how many species you need to cover all functions

-However it is likely that the more species you have, the less functionality each individual would give relative to the whole system.

-Various models for the importance of individual species in an ecosystem. Every species equally contributes to functionality? Some species contribute more (driver and passengers)? Interactions between species can cause boosts and dips in functionality?

Ceder Creek Experiment

-Experiment with species richness and functionality (measured as grass cover, soil nitrate availability) and found functionality increases with species richness.

-However found some redundancy with nitrogen take up - plateaued out after about 15 species.

-If you identify different species, it is not all about number of species, it is dependent on what functions each species has that defines its contribution.

-If you have species that have different nitrogen soil effects then there is more functionality. OR lots of different root depth species.

-Species of contrasting functional properties help to utilise the environment.

- Higher species diversity - higher trait diversity - more functionality and interactions - higher ecological function.

-Holon; term that has ups and downs (+ve and -ve). Similar to a hierarchy but has no absolute top and bottom.

-With ecosystem function, different processes happen at different scales ranging from millenia to seconds.