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4. Ecosystems
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4. Ecosystems
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4. Ecosystems
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Understanding points
Evolution
Change in the
heritable
characteristics of a population
•
Lamarck: acquired characteristics are inherited
•
Darwin: genetic variation within a population leads to selection pressures that allow organisms that are better adapted to the environment to survive and reproduce
Evidence for evolution
Nucleotide and 𝛼𝛼 sequences
The more closely related two species are, the fewer differences in sequence
A4.1 Evolution and speciation
Understanding points
Biodiversity
The total number of different species living in a defined area
1.
Genetic
: the variety in the gene pool of a species
2.
Species
: the number of species present and their
relative abundance
in an area
3.
Ecosystem
: the range of different habitats or number of ecological niches in an ecosystem
Ecosystem
A
community
of organisms and the
abiotic environment
in which they live
•
5 mass extinctions in the past, all due to natural causes
•
6th mass extinction is underway, caused by human activities
A4.2 Conservation of biodiversity
Understanding points
Habitat
The place where an organism lives
•
Includes the geographical location, type of ecosystem, and physical and chemical conditions
•
Biotic
factors: living components of an ecosystem, e.g. plants, animals, bacteria
•
Abiotic
factors: nonliving components of an ecosystem, e.g. air, water, rock
Adaptations to the environment
Sand dunes
Lyme grass
•
Underground stems called
rhizomes
that extend deep into the dune to obtain water
•
Thick waxy cuticle on leaves that reduces transpiration
B4.1 Adaptation to environment
Understanding points
Ecological niche
The unique role of an organism in an ecosystem
•
Fundamental
: the
potential
niche in the absence of competition
•
Realized
: the
actual
niche due to competition
•
Competitive exclusion
: when the fundamental niches of two species overlap, one species outcompetes the other
B4.2.1 Ecological Niche
Types of respiration
B4.2 Ecological niches
Understanding points
Population
A group of individuals of the same species living in an area
•
Carrying capacity
: maximum population size that an environment can support
Estimation of population size
Random sampling
Every member of the species has an equal chance of being selected
Quadrat sampling
Repeatedly placing a quadrat frame at random locations and recording the number of organisms present each time
Only suitable for organisms that do not move (
sessile
)
C4.1 Populations and communities
Understanding points
Open and closed systems
•
Sunlight
is the source of energy for most ecosystems
•
Producers
use this energy to make carbon compounds for consumers
C4.2.1 Open and Closed Systems
Representation of feeding relationships
•
Arrows indicate the direction of energy flow
C4.2 Transfer of energy and matter
Understanding points
Natural selection
D4.1.1 Natural Selection
Sexual selection
•
Male birds of paradise have long, colorful feathers to attract a female
•
These traits are inconvenient and detrimental to their survival but signal their health and strength, increasing their chances of mating (reproductive success)
D4.1 Natural selection
Understanding points
Sustainability
•
Systems are stable if they can continue for an unlimited amount of time
•
Sustainability of ecosystems requires a steady supply of energy, nutrient cycling, tolerable climate, and high genetic diversity
•
Tipping point
: a level of disturbance beyond which irreversible changes occur to the ecosystem
•
A
mesocosm
can be used to model ecosystem sustainability
D4.2.1 Sustainability
Keystone species
Have a disproportionate effect on ecosystem structure
•
Their loss reduces species diversity and may lead to ecosystem collapse
•
e.g. sea stars
D4.2 Sustainability and change
Understanding points
Climate change
D4.3.1 Climate Change
Positive feedback cycles in global warming
Consequences of global warming
Reduced nutrient upwelling
D4.3 Climate change
