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Chapter 53 ~ Community Ecology. Community : an assemblage of populations living close enough together for potential interaction. Community Interactions. Key relationships in the life of an organism are its interactions with other species in the community.
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Community: an assemblage of populations living close enough together for potential interaction
Community Interactions • Key relationships in the life of an organism are its interactions with other species in the community • These relationships are called: INTERSPECIFIC & they involve *Predation (including parasitism; may involve a keystone species/predator) *Competition *Commensalism *Mutualism
KEYSTONE SPECIES:species whose impact on its community or ecosystem is disproportionately large relative to its abundance
The classic example is a seastar (Pisasterochraceus) in the rocky intertidal of the Pacific Northwest: • Pisasterochraceus: efficient predator of the common mussel, Mytiluscalifornicus. • reduces abundance of M. californicus, allowing other macroinvertebrates to persist. • Experimental removal of P. ochraceus results in near total dominance of intertidal by Mytilus to the exclusion of other intertidal macroinvertebrates. • Pisaster present diverse intertidal community • Pisaster absent intertidal community dominated by M. californicus.
http://www.bbc.co.uk/nature/life/Strongylocentrotus_purpuratus#p0038tcchttp://www.bbc.co.uk/nature/life/Strongylocentrotus_purpuratus#p0038tcc
Predation defense • Cryptic (camouflage) coloration • Aposematic (warning) coloration • Mimicry~ superficial resemblance to another species √ Batesian~ palatable/ harmless species mimics an unpalatable/ harmful model √ Mullerian~ 2 or more unpalatable, aposematically colored species resemble each other
Defense? Cryptic coloration Leafy Sea Dragon
Defense? Aposematic coloration Figure 53-06
Green parrot snake Batesian mimicry: hawk moth larva puffs up its head & thorax & looks like a snake! It even weaves & hisses. Hawkmoth larva
Coral snake: one of the most potent venoms! Moth looks like owl eyes.
Mullerian Mimicry LE 53-8 Cuckoo bee Yellow jacket
Competition: a closer look Interference competition within a species • Interference • occurs directly • actual fighting over resources; prevent establishment into an area • Exploitative • occurs indirectly • consumption or use of similar resources (food or space)
Ecological Niche vs. Habitat • ECOLOGICAL NICHE: Sum total of a species use of biotic & abiotic resources in its environment • HABITAT: the environment in which a species normally lives • Analogy: niche is the organisms profession or ecological role in an ecosystem; its habitat is its address
Ecological niche: • fundamental~ the set of resources a population is theoretically capable of using under ideal conditions • realized~ the resources a population actually uses Ex: Barnacle spp. on the coast of Scotland
High tide High tide Chthamalus Chthamalus realized niche Balanus Chthamalus fundamental niche Balanus realized niche Ocean Ocean Low tide Low tide LE 53-2
Trophic Relationships: determine routes of energy flow and chemical cycling • PRIMARY PRODUCERS: autotrophs (usually photosynthetic); -support all other trophic levels by using light or chemical energy to synthesize sugars (e.g. plants, algae, some bacteria like cyanobacteria)
Trophic Relationships 2) PRIMARY CONSUMERS: heterotrophs; herbivores that consume primary producers (e.g. insects, snails, grazing animals, seed-eating & fruit-eating birds and mammals)
Trophic Relationships 3) SECONDARY CONSUMERS: carnivores that eat herbivores (e.g. spiders, frogs, insect-eating birds, carnivorous mammals, etc.)
Trophic Relationships 4) TERTIARY CONSUMERS: carnivores that eat other carnivores -(e.g. hawk that eats snake that eats mouse) -(e.g. human that eats large fish that eats small fish)
Trophic Relationships 5) SAPROTROPH: (decomposers); lives on or in nonliving organic matter; secretes digestive enzyme into it & absorbs the products/nutrients (ex: fungi) **detritivore (decomposer): ingests detritus or nonliving organic matter
FOOD CHAINS • FOOD CHAIN: the pathway along which food is transferred from trophic level to trophic level, beginning with the primary producers
FOOD WEBS • FOOD WEB: more elaborate pathway showing complex feeding relationships
CH 54: ECOSYSTEM • All organisms in a given area along with the abiotic factors with which they interact; • Energy flow and chemical cycling are included at this level **Energy flows through ecosystems and matter cycles within them!
ENERGY IN AN ECOSYSTEM *ENERGY is required for growth, maintenance, and reproduction by all organisms *ultimate source of energy = SUNLIGHT
ENERGY IN AN ECOSYSTEM • an ecosystem’s entire “energy budget” is determined by the photosynthetic activity of the system • as energy flows through an ecosystem, much is lost at each trophic level
ENERGY IN AN ECOSYSTEM • BIOMASS: the dry weight of organic matter comprising a group of organisms in a particular habitat
ENERGY FLOW IN AN ECOSYSTEM • Only about 5-20% of the calories consumed by a consumer are used for growth (which adds biomass to the trophic level). • The remaining organic material consumed is used for cellular respiration or is passed out of the body as feces.
ENERGY FLOW IN AN ECOSYSTEM • The energy in the feces stays in the system and is consumed by decomposers. • The energy used in cellular respiration is lost from the system (in the form of HEAT).
SO… 80-90% of the energy available at one trophic level NEVER TRANSFERS TO THE NEXT!!
This loss of energy in a food chain can be represented by: A pyramid of energy
PYRAMID OF ENERGY: depicts the flow of energy from one trophic level to the next (units:J m-2 yr-1)
Check for understanding… For humans, which is more EFFICIENT? -eating grains? -eating meat?
Answer: eating grains! Why?… • there is more energy (cal or kcal) available at the primary producer level; • energy is “lost” in the form of heat as it moves through trophic levels • We could feed more people with an acre of grains if we eat the grains directly instead of feeding the grains to a cow so we can eat the cow!