Chapter 1: Introduction to the Science of Ecology

Transcription

1 Chapter 1: Introduction to the Science of Ecology 1

2 Just what is ecology, anyway? Root from Greek oikos First used as a word by Henry David Thoreau in

3 Just what is ecology, anyway? Definitions according to Ernst Haekel: total relations of an animal to both it organic and inorganic environment Charles Elton: scientific natural history H.G. Andrewartha: scientific study of the distribution and abundance of organisms Eugene Odum: structure and function of nature 3

4 Just what is ecology, anyway? Definitions according to Charles Krebs: scientific study of the interactions that determine the distribution and abundance of organisms where organisms are found how many occur there why they live there 4

5 History of ecology Hunter-gatherers Agricultural age Egyptians through Aristotle fear of plagues explanations relating to ecology 5

6 History of ecology Advances beginning in the 17 th century John Graunt (c. 1662) father of demography described human populations in quantitative terms Antony van Leewenhoek (c. 1687) reproductive rates of grain beetles, carrion flies (1 pair >740,000 in 3 months), human lice first attempts to calculate theoretical rates of increase for animal species 6

7 History of ecology Advances after the 17 th century Buffon (c. 1756) Georges-Louis Leclerc, Comte de Buffon author of Natural History humans, plants and animals all regulated by the same processes 7

8 History of ecology Advances after the 17 th century Thomas Malthus (c. 1798) author of Essay on Population numbers of organisms increase geometrically, but their relative food supply may never increase more than arithmetically Generation _ Population: Food supply: concluded that food supply limits population size 8

9 History of ecology Advances after the 17 th century Adolphe Quetelet (c. 1835) potential ability of a population to grow geometrically is balanced by a resistance to growth Pierre-François Verhulst (c. 1838) derived equation describing growth of a single population over time: logistic his work was overlooked for 100 years 9

10 History of ecology Advances in the 18 th and 19 th centuries balance of nature versus natural selection recognition of interrelations of organisms within communities Edward Forbes (c. 1844) communities in British coastal waters and Mediterranean zones of different depths with different communities Stephen Forbes (c. 1887) author of The Lake as a Microcosm affecting one species in a community can influence the whole community 10

11 Fig. 1.1 (p. 5): The four biological disciplines closely related to ecology. 11

12 Ecology versus environmental science Ecology: focuses on the natural world of interactions of plants and animals (including humans) with their natural environments Environmental science: focuses on human impacts on the Earth s environments (physical, chemical, biological) 12

13 Approaches to studying ecology Descriptive ecology (what?) Functional ecology (how?) Evolutionary ecology (why?) 13

14 Approaches to studying ecology Evolutionary ecology 14

15 Approaches to studying ecology Functional ecology 15

16 Approaches to studying ecology Descriptive ecology 16

17 Approaches to studying ecology Descriptive ecology 17

18 Approaches to studying ecology Descriptive ecology 18

19 Fig. 1.4 (p. 10): Relationship between distribution and abundance. 19

20 Fig. 1.5 (p. 11): Abundance of the horned lark in North America,

21 Fig. 1.6 (p. 12): Distribution and abundance of the red kangaroo in Australia,

22 Fig. 1.7 (p. 13): Levels of integration studied in biology. 22

23 Levels of integration in biology Species organism level of integration fundamental unit in ecology three-part definition group of actually or potentially interbreeding organisms, that are reproductively isolated from other kinds of organisms, and that produce viable offspring 23

24 Levels of integration in biology Population group of organisms of the same species occupying a given area at a given time unique property = density examples: humans bluebirds fox squirrels 24

25 Levels of integration in biology Community group of interacting populations occupying a given area unique property = species diversity examples: bottomland hardwood plant community coastal prairie plant community bay bottom benthic community 25

26 Levels of integration in biology Ecosystem group of interacting communities, linked by lines of energy transfer abiotic features biotic features examples: Galveston Bay East Texas piney woods pond 26

27 Methods used to study ecology Theoretical (mathematical) Laboratory Field Plant ecology versus animal ecology 27

28 The scientific method 28

29 Chapter 2: Evolution and Ecology 29

30 Ecology and evolution Evolution (in ecological terms) change in traits of a population over time involves changes in the frequency of individual genes in a population from one generation to the next 30

31 What mechanism drives evolution? Neutralists evolution occurs by chance (genetic drift) genetic mutations occur 1/1,000,000 DNA replications some get fixed in the population change 31

32 What mechanism drives evolution? Selectionists evolution is driven by adaptation and natural selection (e.g., Darwin, Wallace in the 1850s) parameters genetic variation excess offspring competition fitness heritability of traits 32

33 How natural selection works Theory The reproductive potential of populations is great, but populations tend to remain constant in size, because populations suffer high mortality. Individuals vary within populations, leading to differential survival of individuals. Traits of individuals are inherited by their offspring. The composition of the population changes by the elimination of unfit individuals. Example Rabbits should be able to cover the whole earth, but they don t, because many are caught by predators. Some rabbits run faster than others and escape from predators. So do their offspring. Populations of rabbits, as a whole, tend to run raster than their predecessors. 33

34 Why natural selection occurs Genetic variability in individuals Heritability of genetic traits Influence of the environment on survival and reproduction 34

35 Processes of evolution Adaptation natural selection acts on phenotypes to cause change in the genetic make-up of a population over time Speciation members of a population become reproductively isolated from each other, leading in time to separate species 35

36 Natural selection by adaptation Natural selection operates on phenotypes Changes in gene frequencies occur only when there is a correlation between phenotype (fitness) and genotype 36

37 Fig. 2.2 (p. 21): Three types of selection on phenotypic characters. 37

38 Fig. 2.3 (p. 21): Directional selection for beak size in the Galapagos ground finch, Geospiza forza. 38

39 Fig. 2.4 (p. 22): Stabilizing selection for birth weight in humans. 39

40 Fig. 2.1 (p. 20): Stabilizing selection for hatching synchrony in lesser snow geese. 40

41 Fig. 2.6 (p. 23): Disruptive selection in the three-spine stickleback in British Columbia, (a) smaller, limnetic form, (b) larger, benthic form. 41

42 Natural selection by adaptation Determination of clutch size in birds David Lack (1947) balance between proximate factors (physiology of the birds that control ovulation and egg-laying) ultimate factors (how many young can successfully fledge, determined by genetic, population and environmental factors) 42

43 Fig. 2.7 (p. 24): Cost-benefit model for evolution of clutch size in birds. 43

44 Fig. 2.8, p. 25): Production of young blue tits in relation to clutch size, Wytham Woods, Oxford, England survival of young birds in manipulated nests is poor. 44

45 Fig. 2.9 (p. 25): Number of house wren chicks fledged from manipulated broods disagreement with Lack s hypothesis. 45

46 Natural selection by adaptation Industrial melanism in the common peppered moth (Biston betularia) 46

47 Natural selection in B. betularia Early 1800s: mostly light form, few melanics (carbonaria) in England Over next 100 years, melanics increased in abundance In some industrialized areas, found only melanics Light or dark forms follow simple Mendelian genetics 1950s: HBD Kettlewell s mark-recapture and ecology studies 47

48 Distribution of light and dark forms of B. betularia in Great Britain, 1950s 48

49 B. betularia mark-recapture study Number of moths Industrial site Light form Dark form Non-industrial site Light form Dark form Marked and released Recaptured Percent recaptured

50 Natural selection in B. betularia What is the specific agent of selection for fitness in the dark form moths? industrial site: tree trunks darker from soot, dark form camouflaged non-industrial site: dark forms stand out on lighter trunks 50

51 Number of B. betularia taken by birds Light form Dark form From trees at nonindustrial site From trees at industrial site

52 Fig. 2.1 (p. 18): Evolution in the common peppered moth in England since

53 Natural selection within a species Favors those individuals who can produce the most offspring number of offspring per mating at 2 per mating: at 3 per mating: number of times individual can reproduce over its lifetime 1 2 young = young = young = 20 53

54 Natural selection within a species Favors those who survive the given environmental conditions (fitness) Offset by parental investment: parental care decreases as number of offspring increases 54

55 Coevolution SPECIES A SPECIES B Specific trait of Species A evolves in response to a specific trait of Species B, which in turn evolves in response to the trait of Species A 55

56 Coevolution Ehrlich and Raven from studies on plants and insects that eat them Specific and reciprocal Diffuse coevolution: >2 species involved SPECIES A SPECIES B 56

57 Examples of coevolution Oryctolagus rabbits and Myxoma virus Tropical ant-plant relationships: melastomes and Inga Cecropia trees and Azteca ants Oropendulas and wasps Amazon water lily (Victoria amazonica) and scarab beetles (Cyclocephala sp) 57

58 Myxoma virus and Oryctolagus rabbits in Australia Rabbits introduced to Australia in late 1800s Rapidly increased in abundance severe problem, destroyed rangelands used for sheep Myxoma common parasite of new world rabbits causes smallpox in balance in S. American rabbit populations 58

59 Myxoma virus and Oryctolagus rabbits in Australia Myxoma introduced as a potent killer of Australian rabbits initially killed 99.8% of the rabbit population within three generations, virus 40-60% effective rabbit populations increased and reached an equilibrium with the virus 59

60 Fig a (p. 248): Population crash of European rabbits in Australia following introduction of Myxoma virus in

61 Fig b (p. 248): Decline in mortality rates of European rabbits in Australia as a function of time after introduction of Myxoma virus. 61

62 Fig c (p. 248): Effect of vaccination on numbers of adult rabbits in fenced areas in SE Australia. 62

63 Myxoma virus and Oryctolagus rabbits in Australia Apparent coevolution between rabbits and Myxoma virus rabbits that were fit (survived and reproduced) were resistant to lethal effects of virus and passed that trait to young simultaneously, Myxoma virus increased its fitness by becoming less virulent virus transmission requires mosquito vector best strategy is intermediate virulence: not kill host before mosquito can transmit 63

64 Tropical ant-plant relationships Primary domatia Melastomataceae 64

65 Tropical ant-plant relationships Primary domatia Melastomataceae Inga 65

66 Cecropia trees and Azteca ants 66

67 Cecropia trees and Azteca ants prostoma septum 67

68 Cecropia trees and Azteca ants 68

69 Cecropia trees and Azteca ants 69

70 Cecropia trees and Azteca ants Bead bodies supply glucose 70

71 Cecropia trees and Azteca ants Mullerian bodies supply glycogen 71

72 Oropendulas and wasps 72

73 Amazon water lily and scarab beetles 73

74 Amazon water lily and scarab beetles Day 1 Day 2 74

75 Amazon water lily and scarab beetles 75

76 Amazon water lily and scarab beetles 76

77 Fig (p. 27): Evolution and arms race between parasitic cowbird and parasitized species that try to defend their nests by ejecting cowbird chicks. 77

78 Fig (p. 28): Evolution and arms races between rough-skinned newt (Taricha granulosa) from western N. America and garter snake (Thamnophis sirtalis) that preys on these newts. 78

79 Evolution by speciation Basic requirement: reproductive isolation between populations Reproductive isolation prevention of mating production of nonviable offspring 79

80 Reproductive isolation Prezygotic (prevention of mating) environmental behavioral mechanical physiological 80

81 Reproductive isolation Postzygotic (production of nonviable offspring) offspring weak, do not survive to maturity developmental problems sterility abnormal gonads segregational F 2 breakdown 81

82 Three hypotheses for speciation 82

83 Three hypotheses for speciation Allopatric (geographic) speciation physical or geographical separation each population undergoes independent evolution, adaptation to separate environment Parapatric speciation part of population enters new habitat no physical barrier Sympatric speciation occurs within population before any differences can be seen 83

84 Units of natural selection Individual Gametic: selection at level of sperm and ova Kin: social organization, altruistic behavior Group: population broken into groups with different genetic, adaptive attributes Sexual: dominance in males or females 84