Ecosystems and relationships
Biology H
Ecosystem ecology
•Ecosystem services encompass all the processes through which natural
ecosystems and their species help sustain human life
•Some examples of ecosystem services:
–Purification of air and water
–Detoxification and decomposition of wastes
–Cycling of nutrients
–Moderation of weather extremes
Energy flow
•An ecosystems energy budget is determined by the amount of
photosynthetic activity of the producers
•Producers use light energy to synthesize organic molecules which are then
used to make ATP in cellular respiration
•Consumers obtain energy from organic molecules produced in lower trophic
levels
•Organisms use food energy for:
–Cell respiration
–Maintaining life processes (homeostasis, growth, development, etc)
–Some is lost in waste products and as heat
•Energy has to constantly be added to an ecosystem
Decomposition
•Decomposition connects all trophic levels
•Detritivores, mainly bacteria and fungi, recycle essential chemical elements
by decomposing organic material and returning elements to inorganic
reservoirs
Primary productivity
•Gross primary productivity (GPP): The amount of light energy converted to
chemical energy by autotrophs in an ecosystem; some is stored by plant,
some is used for life processes
•Net primary productivity (NPP): the amount of chemical energy available to
consumers; also called biomass
Secondary productivity
•Rate at which consumers convert the chemical energy in the food they eat
to their own biomass
–Consumers use energy for life functions but cannot completely digest the
food so only about 10% of the energy consumed is available to the next
trophic level
–Pictured in a pyramid
Types of pyramids
•Pyramid of productivity (at trophic levels)
•Biomass pyramid
•Pyramid of numbers (individuals)
•All are similar in that the bases are wide (lots of producers) and narrow
greatly at the top (few top level consumers) and only have 3-5 trophic levels
Community interactions
•Ecologists call relationships between species in a community interspecific
interactions
•Interspecific interactions affect species survival and reproduction
•Examples are competition, predation, herbivory, symbiosis (parasitism,
mutualism, and commensalism), and disease
•Competition: (-/-)
–Interspecific: between species
–Intraspecific: within a species
–Interference: fighting over resources
–Exploitative: use of resources
–Resource partitioning: each species uses only a part of the resources which
lessons competition
Competition
•Interspecific competition occurs when species compete for a resource in
short supply
•Strong competition can lead to competitive exclusion, local elimination of a
competing species
–The competitive exclusion principle states that two species competing for
the same limiting resources cannot coexist in the same place
Ecological Niches
•The total of a species’ use of biotic and abiotic resources is called the
species’ ecological niche
•Similar species can coexist in a community if there are significant
differences in their niches
•As a result of competition, a species’ fundamental niche (all resources it’s
capable of using) may differ from its realized niche (resources they actually
use)
Predation
•Predation refers to interaction where one species, the predator, kills and
eats the other, the prey
•Some feeding adaptations of predators are claws, teeth, fangs, stingers,
and poison
•Prey display various defensive adaptations
•Behavioral defenses include hiding, fleeing, self-defense, and alarm calls
•Animals also have morphological and physiological defense adaptations
Keystone predator
•Helps maintain biodiversity by eating the best competitor at the next
lowest trophic level
•Examples
•Sea stars in intertidal zones eat mussels which crowd out all other
invertebrates
•Sea otters in kelp forests eat sea urchins which eat through kelp holdfasts
and allow the kelp forest to float away
Mutualism
Commensalism
Defense against predation
•Cryptic coloration: camouflage
•Aposematic coloration: bright, warning coloration
•Batesian mimicry: copy a toxic or dangerous animal
Human Disturbance
•Humans are the most widespread agents of disturbance
•Human disturbance to communities usually reduces species diversity
•Humans also prevent some naturally occurring disturbances, like fires,
which can be important to community structure
Four Major Threats to Biodiversity
•Most species loss can be traced to four major threats:
–Habitat destruction
–Introduced species
–Overexploitation
–Disruption of “interaction networks”