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Ecology lecture 1 summary
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Summary of the lecture of the course Ecology at WUR.
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1 ECOLOGY AND EVOLUTION: THE ORIGIN AND DISTRIBUTION OF SPECIESWHAT IS ECOLOGY AND THE IMPORTANCE OF ECOLOGICAL KNOWLEDGE
Ecology = oikos - house, logia – knowledge à knowledge of the relationship between organisms and
their environment.
“The scientific study of the distribution and abundance of organisms, the interactions that
determine that distribution and abundance, and the relationship between organisms and the
transformation and flux of energy and matter”. à how organisms interact between each other.
Trying to understand the processes that explain these patterns that determine the interaction
between organisms. So, ecology looks at these processes: where are certain individuals? How do
they move? What’s their dispersal and their density? Also, what are the characteristics of the
organism (the characteristics are strongly driven by evolution).
So, the central variable studied are:
• Distribution,
• dispersion,
• density
• characteristics of the organisms that influence distribution.
What do ecologists do? Ecology starts with:
• observation
• discovering patterns
• asking questions
• unravelling underlying processes (understand mechanisms under these questions)
Ecologists use various approaches to do so:
• observation in the field
• controlled field or lab experiments
• mathematical models
• statistics: reliability of findings
• molecular and chemical analysis to help unravel ecological questions.
Ecologists typically ask questions in different ways, and these can be answered in many ways.
We can characterize two different types of answer:
• proximate explanation: (causal-analytical) (how) it’s a cause-effect explanation, so it’s
proximate.
• ultimate explanation: (evolutionary processes) (why), it explains the function.
Lecture 1
1
, ECOLOGY AND EVOLUTION: SPECIATION AND DISPERSION
To understand what is happening today we must go billions of years back in time when life and
planet Earth arise, and we must understand how that life evolved and why we have species and
different characteristic today. The most important events:
• Advent of anaerobic bacteria: The earth is about 4.6 billion years old. At the beginning there
was no atmosphere an all sorts of chemical reactions would occur, dissolving into water and
creating the primordial soup. No free oxygen was present. When the first species evolved
there was a very hostile environment of a volcanic atmosphere, with still no oxygen. There
were anaerobic organisms that first started to use the few compounds that this hostile
atmosphere offered. These are the Archaebacteria (primordial bacteria).
• Photosynthesis and free oxygen: An important step in understanding present day life is
photosynthesis: plants were starting to make oxygen, that was first bound to stone, but
when the concentration started to rise and rise it came free in the atmosphere. The first
photosynthesis organisms emerged about 3.5 billion years ago.
Species are very opportunistic: if there are new resources species will eventually evolve in
using these. So, the organisms started to use oxygen.
• Ozone as a shield against UV: oxygen shields the earth's surface from UV radiation of the
Sun, through the formation of ozone (O3). Thanks to oxygen, life gradually became possible,
between 1 and 0.7 billion years ago.
• Life on land: life started in the water and then started to colonize the lands.
• Sexual reproduction: by sexual reproduction we get a lot of genetic information that
generates the diversity on our planet.
EVOLUTION BY NATURAL SELECTION
Charles Darwin and Alfred Russell Wallace were both ecologists.
Darwin gradually developed the view that the natural diversity was the result of a process of
evolution in which natural selection favoured some variants within species through a ‘struggle for
existence.’ In 1858, Wallace, who had read Darwin’s journal, wrote to Darwin, spelling out the same
theory of evolution. Darwin’s On the Origin of Species was then hastily prepared and published in
1859. It is probably the first major textbook of ecology.
The theory of evolution by natural selection rests on a series of established truths:
1. Individuals that form a population of a species are not identical.
2. Some of the variation between individuals is heritable (genetic basis capable of being passed
down to descendants).
3. All populations could grow at a rate that would overwhelm the environment; but in fact, most
individuals die before reproducing and most reproduce at less than their maximal rate.
4. Different ancestors leave different numbers of descendants. Those that contribute most have
the greatest influence on the heritable characteristics of subsequent generations.
Fitness is the relative contribution of an individual to next generation.
Evolution is the change, over time, in the heritable characteristics of a population or species. Given
the above four truths, the heritable features that define a population will inevitably change.
Evolution is inevitable.
The individuals that determine the direction that evolution takes are those that were best able to
survive the risks and hazards of the environments in which they were born and grew; and those
who, having survived, were most capable of successful reproduction. The philosopher Herbert
Spencer described the process as “the survival of the fittest”.
Lecture 1
2
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