Chapter 53

1. Chapter 53 comm Ecology

2. Overview: What Is a comm? • biological community- pop’s of various spp living close enough for potential interaxn • Animals & plants surrounding a watering hole in southern Africa are members of a savanna comm

4. Concept 53.1: A community’s interactions include competition, predation, herbivory, symbiosis, & disease • relationships b/w spp in a comm are interspecific interactions • Interspecific interactions affect spp survival & reproduction • Ex’s: competition, predation, herbivory, symbiosis (parasitism, mutualism, & commensalism), & disease

6. Competition • Interspecific competition- spp compete for a resource in short supply • Strong competition can lead to competitive exclusion, local elimination of a competing spp

7. The Competitive Exclusion Principle • The competitive exclusion principle- 2 spp competing for same limiting resources can’t occupy the same niche

8. Ecological Niches • ecological niche- total of a spp’ use of biotic & abiotic resources • Ecologically similar spp can coexist in a comm if there are 1 or more significant diff's in their niches • As a result of competition, a spp’ fundamental niche may differ from its realized niche

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

10. Resource Partitioning • Resource partitioning- differentiation of ecological niches, enabling similar spp to coexist in a comm

11. LE 53-3 A. insolitus usually perches on shady branches. A. ricordii A. insolitus A. distichus perches on fence posts & other sunny surfaces. A. aliniger A. christophei A. distichus A. cybotes A. etheridgei

12. Character Displacement • Character displacement- tendency for char’s to be more divergent in sympatric pop's of 2 spp than in allopatric pop's of the same 2 spp • An example is variation in beak size b/w pop's of 2 spp of Galapagos finches

13. LE 53-4 G. fortis G. fuliginosa Beak depth Santa María, San Cristóbal Sympatric pop's 40 20 0 Los Hermanos Percentage of indiv's in each size class 40 G. fuliginosa, allopatric 20 0 Daphne 40 G. fortis, allopatric 20 0 14 10 16 12 8 Beak depth (mm)

14. Predation • Predation- 1 spp, (predator), kills & eats the other, the prey • Some feeding adaptations of predators are claws, teeth, fangs, stingers, & poison

15. Prey display various defensive adaptations • Behavioral defenses include hiding, fleeing, self-defense, & alarm calls • Animals also have morphological & physiological defense adaptations

16. Cryptic coloration/camouflage- makes prey difficult to spot Video: Seahorse Camouflage

18. aposematic coloration- animals w/ effective chem defense often exhibit bright warning coloration • Predators are particularly cautious in dealing w/ prey that display such coloration

20. In some cases, a prey spp may gain significant protection by mimicking the appearance of another spp

21. Batesian mimicry- palatable or harmless spp mimics an unpalatable or harmful model

22. LE 53-7 Green parrot snake Hawkmoth larva

23. Müllerian mimicry- 2 or more unpalatable spp resemble each other

24. LE 53-8 Cuckoo bee Yellow jacket

25. Herbivory • Herbivory refers to an interaction in which an herbivore eats parts of a plant or alga • It has led to evolution of plant mechanical & chemical defenses & adaptations by herbivores

26. Parasitism • In parasitism, 1 organism, the parasite, derives nourishment from another organism, its host, which is harmed in the process • Parasitism exerts substantial influence on pop's & the structure of communities

27. Disease • Effects of disease on pop's & communities are similar to those of parasites • Pathogens, disease-causing agents, are typically bacteria, viruses, or protists

28. Mutualism • Mutualistic symbiosis, or mutualism, is an interspecific interaction that benefits both spp Video: Clownfish & Anemone

30. Commensalism • In commensalism, 1 spp benefits & the other is apparently unaffected • Commensal interactions are hard to document in nature because any close association of 2 spp likely affects both

32. Interspecific Interactions & Adaptation • Coevolution- reciprocal evolutionary adaptations of 2 interacting spp • The term is often used too loosely in describing adaptations within a comm • There is little evidence for true coevolution in most interspecific interactions

33. Concept 53.2: Dominant & keystone spp exert strong controls on comm structure • In general, a few spp in a comm exert strong control on that community’s structure • 2 fundamental features of comm structure are spp diversity & feeding relationships

34. spp Diversity • spp diversity of a comm is the variety of organisms that make up the comm • It has 2 components: spp richness & relative abundance • spp richness- total # of diff spp in the comm • Relative abundance- proportion each spp represents of the total indiv's in the comm

35. 2 communities can have the same spp richness but a different relative abundance • A comm w/ an even spp abundance is more diverse than one in which one or 2 spp are abundant & the remainder are rare

36. LE 53-11 A B C D comm 1 C: 25% A: 25% D: 25% B: 25% comm 2 C: 5% A: 80% D: 10% B: 5%

37. Trophic Structure • Trophic structure- feeding relationships b/w organisms in a comm • It is a key factor in comm dynamics • Food chains link trophic levels from producers to top carnivores Video: Shark Eating a Seal

38. LE 53-12 Quaternary consumers Carnivore Carnivore Tertiary consumers Carnivore Carnivore Secondary consumers Carnivore Carnivore Primary consumers Herbivore Zooplankton Primary producers Plant Phytoplankton A terrestrial food chain A marine food chain

39. Food Webs • food web- branching food chain w/ complex trophic interactions

40. LE 53-13 Humans Smaller toothed whales Sperm whales Baleen whales Elephant seals Leopard seals Crab-eater seals Fishes Squids Birds Carnivorous plankton Euphausids (krill) Copepods Phyto- plankton

41. Food webs can be simplified by isolating a portion of a comm that interacts very little w/ the rest of the comm

42. LE 53-14 Sea nettle Juvenile striped bass Fish larvae Zooplankton Fish eggs

43. Limits on Food Chain Length • Each food chain in a food web is usually only a few links long • 2 hypotheses attempt to explain food chain length: the energetic hypothesis & the dynamic stability hypothesis

44. The energetic hypothesis suggests that length is limited by inefficient energy transfer • The dynamic stability hypothesis proposes that long food chains are less stable than short ones • Most data support the energetic hypothesis

45. LE 53-15 6 6 No. of spp 5 5 No. of trophic links 4 4 # of spp # of trophic links 3 3 2 2 1 1 0 0 Medium Low High (control) Productivity

46. spp w/ a Large Impact • Certain spp have a very large impact on comm structure • Such spp are highly abundant or play a pivotal role in comm dynamics

47. Dominant spp • Dominant spp- most abundant or have the highest biomass • They exert powerful control over the occurrence & distribution of other spp

48. One hypothesis suggests that dominant spp are most competitive in exploiting resources • Another hypothesis is that they are most successful at avoiding predators

49. Keystone spp • In contrast to dominant spp, • keystone spp- not necessarily abundant in a comm but exert strong control on a comm by their ecological roles, or niches

50. Field studies of sea stars exhibit their role as a keystone spp in intertidal communities