Definitions
• Ecology defined by interactions and interconnections –
with own species, other species, environment; organisms
affect each other, environment; environmental factors
affect organisms and activities.
• Organisms and envt. factors:
Species - group of actively or potentially interbreeding
individuals reproductively isolated from other such
groups
Population - all individuals of a species in a discrete area
Community – a group of populations of species that occur
together and interact
Ecosystem – functional unit; community and surrounding
physical and chemical environment.
– Large, complex, component studies
– Ocean ecosystems – different physico-cemical factors, different
biotic effects,
– Drives adaptation, changing composition
Energy - Trophic Structure
Autotrophs
standing crop/biomass
productivity
Heterotrophs
Decomposers
Food chain
Trophic levels
Food web
Biogeochemical cycles
Carbon Cycle
• Source
• Sink
• Self limiting feedback
Limiting factors
• Energy – how it enters, how it moves,
where is it stored
• Abiotic factors – tolerance range for
physical, chemical
• Interactions with other organisms
Environment
Niche - ecological role of a species in the community
Fundamental niche – all the ecological conditions where an
organism could exist, roles it could play
Realized niche – actual conditions where organism does exist,
roles it does play (real world distribution)
Niche Breadth - range of conditions tolerated or resources
used by an organism
• Specialist – narrow range of conditions tolerated,
resources used
• Generalist – broad range of conditions tolerated,
resources used
– place where an organism is found (more general)
Niche
Fundamental niche
Salinity
Realized niche
Temperature
Interaction
Reproductive potential >> natural
population.
Limits to explosive growth?
• Competition
• Predation
• Parasitism and disease
Competition – interaction among organisms for a
necessary resource that exists in short supply
- Interspecific
- Intraspecific
• Interference - one individual exerts negative
effects/actively prevents another from getting resources
• Exploitation - one individual exploits a resource at a
higher rate than another (less direct)
Competitive exclusion principle (Gause’s
principle 1934) – no 2 species with the same
requirements can exist in the same space at
the same time
Niche overlap
competition outcomes.
•Competitors coexist
•Stronger competitor
displaces weaker
Conditions for Coexistence:
– magnitude of competitive effect on both is low
(food supply, abiotic conditions)
– superior competitor is kept at low densities
Competitive relationships:
hierarchical
A>B>C
network
A > B, B > C, but C > A
Community structure – make-up of species in a community
Species richness – number of species
Species evenness – distribution of individuals among the species
“Diversity” combines richness and evenness
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Species
Species
Dominant species – species with greatest number of individuals or biomass
Population limiting factors – biological and physical
• Density-dependent
• Density-independent
Leibig’s Law of the Minimum – that life requirement or
essential resource that is first reduced below the
minimum (in shortest supply) will limit growth and
survival
Resource renewal – can be active or passive, rate affects
population growth
Exponential growth – growth without limits
Logistic growth – density-dependent growth
Predation –
Predators can prevent competitive exclusion, allow
coexistence
Predator avoidance strategies
• rapid reproduction
• refuges
Optimal foraging theory – predators select prey to
maximize rate of food intake
Predation : consumption of one
organism by another
• Effect can vary
– Large change in prey density = predatory
control (Paine’s starfish)
– Little/no change = little control effect (least
tern)
• Keystone species
• Trophic cascade
Figure 5: CPUE per lunar month of
Stolothrissa and Lates stappersii (mukeke)
Predation: a force to structure communities -Pisaster, a starfish, keystone predator. in the absence of Pisaster, a few
competitive dominants (barnacles and mussels) can usurp all the space in the intertidal.
Pisaster predation can free up areas of rock that can then be used by other species
such as anemones.
2) Sea otters reduce sea urchins and increase kelp -- The kelp "forests", in turn,
provide habitat complexity, prey refuges and spawning sites (e.g., for herring) that
seems to increase the diversity of species that can exist.
Population life history strategies
• A continuum; two types (MacArthur) define extremes.
• Opportunistic or R-strategy – short life, rapid maturity,
•
many reproductions/yr., high death rates, larvae usually
present. Usually, small, sedentary and inefficiently use
resources, poorer competitors. Highly variable numbers
Equilibrium or K-strategy – long life, long development
time to maturity, proliferate slowly, ne or few
reproductions/yr., low death rates. Usually larger than
opportunists, mobile, efficiently use resources, better
competitors. Fairly constant numbers.
• Opportunists favored where disturbance is
frequent (waves, sedimentation,
predators). Why?
• Why do bottom samples usually contain
both types?
• Why do proportions change over an area?
• Why do the change with depth?
Password is wfb279
• For Thursday read
• Strathman “Why does a larva swim so
long?” and
• Vance “Reproductive strategies in mrien
benthic invertebrates”