What is a system?
What do we mean by connectedness?
The biosphere is composed of a
hierarchy of complex systems:
•subsystems embedded within
systems—levels of organization
•ecological systems can be as small
as individual organisms and as large
and inclusive as the whole biosphere
What is ecology about?
•from the Greek “Oikos” which
means household
What is Ecology?
• The total relationship of organisms to environment, and
to each other, Ernst Haeckel 1870
• The struggle for existence. Charles Darwin 1859
• The study of the factors affecting the distribution and
abundance of organisms, Charles Krebs 1970.
• The scientific study of the natural environment and the
relationships of organisms to one another and their
surroundings—Ricklefs 2001.
There are different ways of looking at the
relationships of organisms to their environment
•Some ecologists classify habitats and
examine the relationship between organisms
and the habitats they occupy
•Others are more concerned with functional
roles of different types of organisms within
food webs and ecosystems—the ecological
niche
Populations of living organisms are constantly evolving and
adapting to change:
•Evolution as a long, slow process of change tracking the global environment
•Evolution can be a complex arms race, predators are constantly evolving better
tactics and prey are constantly evolving better defence—coevolution can be rapid.
•Evolution is constantly producing new “variants” –diversification
•Evolution is constantly changing and diversifying organisms, which in turn
changes the “systems” that they are a part of, and in the long-term can change
even the global environment itself.
Functional connections: who eats who?
Throughout the history of life, plants, animals and microorganisms have evolved to
carry out different and complimentary functions in natural systems
Eukaryotes arose when
some prokaryotes evolved
the ability to live inside
other cells and function as
organelles within them
Absorb and process dissolved organic matter
Some eubacteria became autotrophs
Protozoa feed on tiny bacteria and other
organic particles
Algae became “green” through bacterial
symbionts which evolved into chloroplasts
Some algae evolved roots, a vascular system
and a cuticle –bacame terrestrial autotrophs
Some protists evolved “hyphae” for the
absorption of organic matter, became
decomposers and pathogens
Some protists evolved into active ingestive
heterotrophs that eat other organisms
Environments influence organisms but organisms also change their environment
Over millions of years the activities of organisms have profoundly changed
the global environment
Evolution can occur rapidly when the
environment changes and natural selection
is very strong—especially where there are
strong interactions among species.
In some cases we’ve been able to observe it
directly—some examples.
The industrial
heart of England
Industrial melanism and the British peppered moth—Biston betularia
•In 1849, a coal-black mutant was found near Manchester,
England. Within a century, this black form had increased to 90%
of the population in this region.
•Offspring of the black mutant were also black (heritable)
•The moth flies at night and rests by day on tree trunks.
•In areas far from industrial activity, the trunks of trees are
encrusted with lichens
•As the photos show, the light form (circled in red) is practically
invisible against this background.
•In areas where air pollution is severe, the combination of toxic
gases and soot has killed the lichens and blackened the trunks.
•Against such a background, the light form stands out sharply.
•The moth is preyed upon by birds that pluck it from its resting
place by day.
•In polluted woods, the dark form has a much better chance of
surviving undetected.
•When the English geneticist H. B. D. Kettlewell released moths
of both types in the woods, he observed that birds did, indeed, eat
a much higher fraction of the light moths he released than of the
dark.
•Since pollution abatement programs were put in place after World
War II, the light form has been making a comeback in the
Liverpool and Manchester areas.
• Modern day examples of how natural selection can operate to
produce evolutionary adaptation to a changing environment
• For example, the bent grass (Argrostis tenuis) in this photo is
growing on the tailings of an abandoned mine, rich in toxic
heavy metals.
•Only plants with genes for
metal tolerance survive.
•Individual plants do not
become more metal
tolerant during their
lifetimes.
•Populations transplanted
back to “clean” soil, lose
their metal tolerance over
a few generations. Why?
Fig. 23.1
Ecologists study the natural world by observation and experiment
Testing hypotheses by experiment: here bird predators that eat
caterpillars are being excluded from an oak sapling in order to test for their effect.
Microcosm experiments:
•Real ecosystems are often huge and hard to replicate and control.
•Microcosms allow us to test hypotheses on scaled down systems that can be replicated.
Humans have long been a prominent part of the environment
Species introductions beyond their
native range:
•both intentional and accidental
Eg the Nile perch
Humans influence ecosystems through exploitation which can
have very complex effects, because of the interconnections in natural systems
Ecologically, we are victims of our own enormous success
at exploiting, manipulating and substituting resources
Sea otters have a huge effect on west coast kelp forests