1. Community Ecology Key Question How does Species Diversity Affect the Sustainability of a Community

2. Organisms have a Habitat and a Niche in an Ecosystem Example: Zebra Mussels Habitat: freshwater lakes, rivers and streams Niche: feeds on green algae

3. Habitat vs. niche Habitat – Space an organisms inhabits Where it lives Its address – Several species can share the same habitat – Based on biological requirements Niche – Functional role of an organism Its job – unique to each organism – How it affects other organisms and the environment

4. Key Question What role do species play and how do they interact in a Community? Niche Structure = how many occur, how unique are they, and how do species occupying different niches interact

5. Role of Species in an Ecosystem Native: Normally live and thrive in a particular ecosystem Alien: Deliberately or accidentally introduced to an ecosystem - An invader Indicator: Marks a specific condition in the ecosystem or serves as an early warning to degradation Keystone: maintains diversity in the ecosystem, positively affects other organisms, top predator keystone species regulate populations Foundation species: Help create habitats and ecosystems

10. Organisms living in direct contact can benefit or harm each other as they interact

11. Relationships Between Organisms Symbiosis – Long term relationship between organisms of two different species living in direct contact – Mutualism – benefits both organisms – Parasitism – benefits one and harms the other organism – Commensalism – benefits one organisms while the other is not affected

12. Trials of Life Pt1 Trials of Life Pt2 Trials of Life Pt3 Trials of Life Pt4

13. mutualism

14. Mutualism between acacia trees and ants Ants feed on nectar and protein rich sacks Attack and sting invading Insects and eat fungal spores Prune back nearing vegetation Tree is protected from invasion Provides home and food for the ant

15. Parasitism negatively effects population growth Parasite = organism that takes nourishment from a host organism sea lamprey

16. Parasitism – Misletoe

17. Commensalism

18. What type of relationship exists between these organisms?

20. Predator/Prey Relationships Are not symbiotic – One species (the predator) feeds directly on another species (the prey) - they are not in long association with each other

21. Predation Plays an ecological role in evolution by natural selection – Predators kill less fit members of a population – Survivors reproduce offspring with adaptations that help them avoid predation Controls population levels – Adaptations to decrease the impact of predators (protection mechanisms) clumping run, swim, fly highly developed sight and smell shells, bark, thorns, chemicals (stinging nettles, skunk, octopus) camouflage (insects, birds) mimicry (viceroy butterfly) Deceptive markings Warning coloration

22. Predator – prey relationships are usually cyclical

27. Platable or harmless species Larval stage of hawkmouth moth Unpalatable or poisonous snake

28. Coral snake Milk Snake

29. Cross-mimicry: benefiting both Predators learn to avoid coloration pattern

30. Peppered Moth

31. Interspecific Interactions – effects on population

32. Key Question How do Communities Respond to Changing Environmental Conditions?

33. Ecological Succession Communities gradually change their structure and species composition in response to environmental conditions (depend on biotic and abiotic factors) - 2 types 1. Primary succession – establishment of a community from barren ground – can take thousands of years to form fertile soils 2. Secondary succession – in response to disturbance - can be positive as nutrients are cycled and new niches open up Intermediate Disturbance Hypothesis - Fairly frequent but moderate disturbance leads to increased species biodiversity (richness and evenness

34. Primary succession – gradual establishment of community in a lifeless area Secondary succession

35. Succession on Mt. St. Helens

36. Population A group of the same kind of organisms (of a single species) living in a given space at a given point in time Defined by: – type – time – Space

37. Key Question What limits the growth of populations?

38. Populations establish various distribution patterns (dispersion) 3 types – Clumping Most common – example: schools of fish Size / location varies with availability of resources – Species clump toward resources Provides protection from predators and therefore population decline Increases ability to catch prey Groups form for mating and caring for young – Uniform dispersion Provides access to scarce resources – Random dispersion (fairly rare)

40. Clumped dispersion: buffalo, swans, fish, lupine

41. Four rates determine change in population size – Natality = birthrate: number of births per unit time – Mortality = death rate: number of deaths per unit time – Immigration: number of individuals moving into a population over time – Emigration: number of individuals moving out of a population over time Additions = removals Effect on Population size positive negative positive negative Zero growth

42. Dispersal The ability of populations to spread from a central place – Active – animals – Passive – plants: move by other organisms or mechanisms – Barriers block dispersal Physical: mountains, water, land forms, food source Behavioral: pack mentality, breeding preferences, territorialism, tradition

43. Limiting Factor Principle – Any abiotic or biotic factor may be critical to the success of organisms and affect the growth of a population (even if other factors are optimal)

44. The best soils for agriculture have no or few limiting factors.

45. Population Growth Limiting Factors Density Dependent - Effect is independent of how big population is Weather: wind, rain, drought, fire, hurricane Human activities: pesticides, clear cutting Density Dependent – Effect depends on the density of the population – 1. Competition for shared or limited resources Resources / food Space - crowding stress – Dense populations result in higher infant mortality – 2. Predation – 3. Parasitism or diseases that spread

47. Stress due to crowding limits population

48. Predators – Density dependent limiting factor

49. Population Growth Curves No population can grow indefinitely

50. Species have a “biotic potential” for population growth Intrinsic rate of increase (r) = inherent reproductive capacity – unlimited resources – no limiting factors Examples: bacteria, geese, humans – Results in exponential growth J-shaped growth curve

52. Exponential Growth The larger a population gets the faster it grows Lag phase: Positive growth starts slowly Boom phase: Exponential growth

53. Example of exponential population growth in nature

54. Carrying Capacity (K) The maximum population a habitat can support without degrading the environment – Abiotic and biotic factors limit population size Competition Scarce resources – Environmental resistance – combination of all factors that limit population growth – Carrying capacity is determined by the combination of biotic potential and environmental resistance

55. Homeostasis – A Stable equilibrium Growth rate decreases as a population reaches carrying capacity Growth rate averages zero Population reaches equilibrium = Maintenance of stability in numbers of individuals Viewed over a long period of time Takes into account fluctuations in population density Populations are dynamic and changing

56. Homeostasis – maintaining stability

57. Populations usually carrying capacity and growth stabilizes Logistic growth = growth with limits curve (s-shaped) Homeostasis

59. Fig. 6-11, p. 119 Exponential growth Environmental resistance Population stabilizes Carrying capacity (K) Biotic potential Time (t) Population size (N)

60. Fig. 6-12, p. 119 Population recovers and stabilizes Carrying capacity Population runs out of resources and crashes Exponential growth Population overshoots carrying capacity Year Number of sheep (millions)

61. Reproductive strategies and population fluctuations (most organisms have reproductive patterns between (r) and (K)) 2 categories – K-strategists (Deer, lion, whale, human) = competitors Large organisms, long lives, produce few offspring, provide care for offspring Populations stabilize at carrying capacity Controlled by density-dependent limiting factors – r-strategists (insects, mice, fish) = opportunists Small, short life, produce many offspring (high capacity for population increase) Produce many offspring but don’t reach carrying capacity High mortality among young (little parental care) Populations fluctuate wildly (boom and bust model) Controlled by density-independent limiting factors

62. Growth Rate Curves K-strategist vs. r-strategist

63. Predator – prey relationships cause population fluctuations

64. Class data TreatmentAve K value Ave r value control5.3.57 Saline - low8.44 medium9.3 high8.36 PO4 - low12.7.68 medium9.50 high14.5.52 NO3 - low14.26 medium6.5.30 high7.39 Shade - low9.5.287 medium6.219 high5.107 Ph 59.288 Ph 622.231 Ph 77.357 Ph 8 Ph 9 7.3.92.057