Chapter 53 ~ Community Ecology

1. Chapter 53 ~ Community Ecology

2. Community: an assemblage of populations living close enough together for potential interaction

3. 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

4. KEYSTONE SPECIES:species whose impact on its community or ecosystem is disproportionately large relative to its abundance 

5. 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.

6. http://www.bbc.co.uk/nature/life/Strongylocentrotus_purpuratus#p0038tcchttp://www.bbc.co.uk/nature/life/Strongylocentrotus_purpuratus#p0038tcc

7. 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

8. Defense?  Cryptic coloration Leafy Sea Dragon

9. Defense?  Aposematic coloration Figure 53-06

10. Green parrot snake Batesian mimicry: hawk moth larva puffs up its head & thorax & looks like a snake! It even weaves & hisses. Hawkmoth larva

11. Coral snake: one of the most potent venoms! Moth looks like owl eyes.

12. Mullerian Mimicry LE 53-8 Cuckoo bee Yellow jacket

13. 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)

14. 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

15. 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

16. High tide High tide Chthamalus Chthamalus realized niche Balanus Chthamalus fundamental niche Balanus realized niche Ocean Ocean Low tide Low tide LE 53-2

17. 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)

18. Trophic Relationships 2) PRIMARY CONSUMERS: heterotrophs; herbivores that consume primary producers (e.g. insects, snails, grazing animals, seed-eating & fruit-eating birds and mammals)

19. Trophic Relationships 3) SECONDARY CONSUMERS: carnivores that eat herbivores (e.g. spiders, frogs, insect-eating birds, carnivorous mammals, etc.)

20. 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)

21. 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

24. FOOD CHAINS • FOOD CHAIN: the pathway along which food is transferred from trophic level to trophic level, beginning with the primary producers

26. FOOD WEBS • FOOD WEB: more elaborate pathway showing complex feeding relationships

27. Web

28. 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!

29. ENERGY IN AN ECOSYSTEM *ENERGY is required for growth, maintenance, and reproduction by all organisms *ultimate source of energy = SUNLIGHT

30. 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

31. ENERGY IN AN ECOSYSTEM • BIOMASS: the dry weight of organic matter comprising a group of organisms in a particular habitat

32. 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.

33. 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).

34. SO… 80-90% of the energy available at one trophic level NEVER TRANSFERS TO THE NEXT!!

35. This loss of energy in a food chain can be represented by: A pyramid of energy

36. PYRAMID OF ENERGY: depicts the flow of energy from one trophic level to the next (units:J m-2 yr-1)

37. Check for understanding… For humans, which is more EFFICIENT? -eating grains? -eating meat?

38. 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!