Community Ecology (Ch.4)

Transcription

1 organism Community Ecology (Ch.4) population community ecosystem biosphere

2 Community Ecology Community all the organisms that live together in a place Community Ecology study of interactions among all populations in an environment To answer: In what way do the populations interact?

3 High tide Niche An organism s niche is its ecological role habitat = address vs. niche = job Competitive Exclusion If Species 2 is removed, then Species 1 will occupy whole tidal zone. Low tide But at lower depths Species 2 out-competes Species 1, excluding it from its potential (fundamental) niche. Species 1 Species 2 Chthamalus sp. Fundamental niches Realized niches Semibalanus sp.

4 Niche & competition Gauss Competitive Exclusion Principle No two similar species can occupy the same niche at the same time

5 Resource partitioning Reduce competition through microhabitats

6 A. insolitus usually perches on shady branches. A. ricordii the ghost of competition past A. distichus perches on fence posts and other sunny surfaces. A. distichus A. alinigar A. insolitus A. christophei A. cybotes A. etheridgei

7 Interspecific interactions Symbiotic interactions competition (-/-) predation / parasitism (-/+) mutualism (+/+) commensalism (+/0)

8 mutualism +/+

9 commensalism +/0

10 Parasitism +/-

11 Predation (or herbivory) +/-

12 Competition -/-

13 What relationship is this?

14 Predation drives evolution Predators adaptations locate & subdue prey Prey adaptations elude & defend horns, speed, coloration Predation provides a strong selection pressure on both prey & predator spines, thorns, toxins

15 Coevolution in Community Predator-prey relationships Parasite-host relationships Flowers & pollinators Long term evolutionary adjustments between species

16 Anti-predator adaptations Hide from predators avoid detection camouflage Warn predators advertise how undesirable you are as prey aposematic coloration apo = away & sematic = sign/meaning

17 Defense mechanisms Camouflage cryptic coloration whipporwill frog lizard lizard toad

18 Mimicry Batesian mimicry Convergent evolution palatable or harmless species mimics a harmful one (a) Hawkmoth larva hawkmoth larvae (b) Green parrot snake green parrot snake Hawkmoth larva puffs up to look like poisonous snake

19 Batesian mimicry Convergent evolution Monarch male Viceroy male poisonous edible Which is the moth fly vs. vs. the the bee? bee? fly bee moth bee

20 Mullerian mimicry two or more protected species look like each other cuckoo bee (a) Cuckoo bee yellow jacket Mullerian mimicry - group defense? - predators may evolve innate avoidance

21 Common warning coloration Aposematic species come to resemble each other black, red, orange & yellow means: DON T EAT ME!

22 What kind of mimicry? Coral snake is poisonous King snake is not Red on yellow, poison fellow; red on black, safe from attack

23 Characterizing a community Community structure species diversity how many different species composition dominant species most abundant species or highest biomass (total weight) keystone species changes over time succession

24 Species diversity greater diversity = greater stability Greater biodiversity offers: more food resources more habitats more resilience in face of environmental change Genetic diversity in a vole population Species diversity in a coastal redwood ecosystem Community and ecosystem diversity across the landscape of an entire region

25 The impact of reduced biodiversity compare these communities suburban lawn agricultural monoculture old field Irish potato famine 1970 US corn crop failure

26 Keystone species Pisaster ochraceous Influential ecological role exert important regulating effect on other species in community keystone species increases diversity in habitat Sea star diversity increases diversity decreases mussels out-compete other species Washington coast

27 Number per Grams per Otter number 0.25 m 2 (% max. count) Keystone species Sea otter is a keystone predator in North Pacific What is the impact of the Orca whale? Food chain before killer whale involvement in chain (a) Sea otter abundance (b) Sea urchin biomass 0.25 m Year (c) Total kelp density Food chain after killer whales started preying on otters

28 Keystone species Beaver is a keystone species in Northeast & West dams transform flowing streams into ponds creating new habitat

29 Ecological succession Sequence of community changes transition in species composition over time years or decades usually after a disturbance Mt. St. Helens

30 Soil nitrogen (g/m 2 ) Primary succession make soil{ Begins with virtually lifeless area without soil, then bacteria lichens & mosses grasses shrubs trees Pioneer Dryas Alder Spruce Successional stage (d) Nitrogen fixation by Dryas and alderincreases the soil nitrogen content. (c) Spruce stage (b) Dryas stage

31 Secondary succession Existing community cleared, but base soil is still intact burning releases nutrients formerly locked up in the tissues of tree the disturbance starts the process of succession over again

32 Succession of species pioneer species compete well in high sunlight lichens & mosses more shade tolerant species grasses climax forest shade tolerant species stable community bushes & small trees trees

33 What causes succession? Tolerance early species are weedy r-selected tolerant of harsh conditions Facilitation & Inhibition early species facilitate habitat changes change soil ph change soil fertility change light levels allows other species to out-compete

34 Climax forest Plant community dominated by trees Representing final stage of natural succession for specific location stable plant community remains essentially unchanged as long as site remains undisturbed birch, beech, maple, hemlock oak, hickory, pine

35 Climax forest taiga The species mix of climax forest is dependent on the abiotic factors of the region solar energy levels temperature rainfall fertility & depth of soil temperate deciduous forest birch, beech, maple, hemlock

36 Disturbances as natural cycle Disturbances are often necessary for community development & survival - release nutrients - increases biodiversity fire climax forests - increases habitats - rejuvenates community

37 Fire climax species Jack Pine adaptations to survive and reproduce in areas than experience frequent fires

38 When people don t learn ecology! Building homes in fire climax zones preventing fires makes next year s fire much worse!

39 Don t blow your top! Ask Questions!

40 Review Questions

41 1. Two barnacles, Balanus and Chthamalus, can both survive on the lower rocks just above the low tide line on the Scottish coast, but only Balanus actually does so, with Chthamalus adopting a higher zone. Which of the following best accounts for this niche separation? A. competitive exclusion B. predation of Chthamalus by Balanus C. cooperative displacement D. primary succession E. mutualism

42 2. Dwarf mistletoes are flowering plants that grow on certain forest trees. They obtain nutrients and water from the vascular tissues of the trees. The trees derive no known benefits from the dwarf mistletoes. Which of the following best describes the interactions between dwarf mistletoes and trees? A. mutualism B. parasitism C. commensalism D. facilitation E. competition

43 3. In a particular case of secondary succession, three species of wild grass all invaded a field the first growing season after a farmer abandoned the field. By the second season, a single one of the wild grasses dominated the field. A possible factor in this succession was A. equilibrium. B. facilitation. C. immigration. D. inhibition. E. mutualism.