Chapter 4 EVOLUTION, BIOLOGICAL COMMUNITIES, AND SPECIES INTERACTIONS

Transcription

1 Chapter 4 EVOLUTION, BIOLOGICAL COMMUNITIES, AND SPECIES INTERACTIONS 1

2 CHAPTER 4 OUTLINE Evolution Ecological Niche Species Interactions Community Properties Communities Change Over Time 2

3 Where is this??? Hint... Darwin s theory of evolution began here! 3

4 ADAPTATION Why do some species live in one place but not another? They have certain adaptations ADAPTATION (verb) - the acquisition of traits that allow a species to survive in its environment ADAPTATION (noun) - a trait that allow a species to survive in its environment ie: The process of adaptation is explained by CHARLES DARWIN S THEORY OF EVOLUTION by natural selection. 4

5 NATURAL SELECTION & EVOLUTION A trait must be inherited (genetic) for evolution to occur. NATURAL SELECTION - Individuals with traits that make them suited to a particular environment survive and reproduce at a greater rate in that environment than individuals with less suitable traits. Over time (multiple generations) the proportion of genes in the population for favorable traits increases. The proportion of genes for unsuitable traits declines. Thus, adaptation occurs. 5

6 LAMARK S THEORY OF EVOLUTION An organism can inherit a trait ACQUIRED by its parents. NOOOO!!!!! 6

7 MUTATION Where do the differences in the genes within individuals come from? MUTATION - changes in DNA sequence that occur by chance (random mistakes in DNA replication, exposure to radiation, etc.) These changes may lead to changes in genes that hold importance for a species. 7

8 SELECTION PRESSURES It is the environment that gives certain mutations an advantage under those particular conditions and causes other variants to be a disadvantaged. THE ENVIRONMENT EXERTS SELECTIVE PRESSURES. NO VARIATION IS INHERENTLY GOOD OR BAD. As environments change, the trait being selected for will change. A trait that was once selected against can be selected for if the environment changes. 8

9 Selection Pressures PEPPERED MOTHS Before the Industrial Revolution in Europe the white variety was favored. As pollution increased, trees were darkened by soot from the burning of coal. The black variety was then favored and its population increased. 9

10 WHAT IS THE DIFFERENCE BETWEEN CAT PAWS BELOW? CHEETAH LION 10

11 EVOLUTIONARY PATHWAYS 1. ADAPTIVE RADIATION A. GENERAL: species develop a radical new ability to reach different parts of the env. ie: birds fly B. ENVIRONMENTAL CHANGE: due to large changes in the env. species branch out to occupy new niches. ie: rapid spread of mammals after the dinosaurs died out C. GEOGRAPHIC ISOLATION: isolated ecosystems are colonized and species change rapidly. ie: Galapagos finches 11

12 EVOLUTIONARY PATHWAYS 2. COEVOLUTION Where two or more species develop and affect each other s evolution, usually due to a close ecological relationship ie: COEVOLUTION CAN BE BENEFICIAL or HARMFUL Hummingbirds feed on deep flowers Parasites feeding on their host 12

13 EVOLUTIONARY PATHWAYS 3. CONVERGENT EVOLUTION different unrelated organisms acquire similar (analogous) characteristics. ie: wings on birds, insects, bats fins on dolphins and sharks 13

14 EVOLUTIONARY PATHWAYS 4. DIVERGENT EVOLUTION initially related organisms become more and more dissimilar ie: arm formation on humans, cats, whale and bat 14

15 EVOLUTIONARY PATHWAYS 5. PARALLEL EVOLUTION when two independent species evolve at the same time and acquire similar characteristics ie: Cichlid fish in different lakes 15

16 EVOLUTIONARY PATHWAYS 6. GRADUALISM & PUNCTUATED EQUILIBRIUM GRADUALISM slow process over millions of years, step by step change PUNCTUATED EQUILIBRIUM rapid speciation over thousands of years probably due to an extreme change in the environment 16

17 LIMITATIONS ON WHERE ORGANISMS LIVE Environmental factors that determine where an organism can live include: Physiological stresses ie: inappropriate levels of moisture, temperature, ph, etc. Competition with other species Predation Parasitism Disease Chance - individuals move to a new and suitable location by chance e.g. organism moved to a different beach after a storm 17

18 CRITICAL LIMITS Von Liebig proposed that the single factor in shortest supply relative to demand is the CRITICAL FACTOR in species distribution Shelford expanded this idea by stating that each environmental factor has both minimum and maximum levels, TOLERANCE LIMITS, beyond which a particular species cannot survive or is unable to reproduce. The factor closest to the limits is the critical factor that determines where an organism can live. 18

19 CRITICAL LIMITS for HUMANS You can live 3 minutes without air You can live 3 hours without shelter You can live 3 days without water You can live 3 weeks without food 19

20 TOLERANCE LIMITS Genetic mutation could cause an individual of a species to have higher tolerance to one factor than other of its kind. This may lead to adaptation & possibly evolution. 20

21 CRITICAL LIMITS For some species, the interaction of several factors, rather than a single limiting factor, determines their BIOGEOGRAPHICAL DISTRIBUTION. Tolerance limits may affect the distribution of young differently than adults. Species requirements and tolerances can also be used as useful indicators of specific environmental characteristics. ie: Trout require clean, well oxygenated water so their disappearance from a stream may indicate that it is being polluted. 21

22 HABITAT AND ECOLOGICAL NICHES HABITAT (HOME) the place or set of environmental conditions in which a particular organism lives ECOLOGICAL NICHE (JOB) describes either the role played by a species in a biological community or the total set of environmental factors that determine a species distribution GENERALIST - has a broad niche (rat) eats anything and lives anywhere! SPECIALIST - has a narrow niche (panda) eats bamboo and lives in mountain forests 22

23 ENDEMIC SPECIES SPECIES SUITED TO LIFE IN ONE PARTICULAR, USUALLY ISOLATED AREA Giant Sequoia (Redwood) is endemic to California Tortoises of the Galápagos Ring-tailed Lemurs of Madagascar Saguaro Cactus in Arizona/Mexico 23

24 COMPETITIVE EXCLUSION G. F. Gause proposed the COMPETITIVE EXCLUSION PRINCIPLE which states that no two species can occupy the same ecological niche at the same time. The one that is more efficient at using resources will exclude the other. This can explain why invasive species sometimes create environmental issues. ie: zebra mussels (Asia) on fresh water mussel (US) 24

25 RESOURCE PARTITIONING RESOURCE PARTITIONING when two or more species co-exist in a habitat by utilizing different parts of a single resource. ie: Birds eat insects during the day and bats eat insects at night. ie: African savanna herbivores eat different parts of the grasses. - - elephant top - zebra middle - antelope bottom 25

26 RESOURCE PARTITIONING Leads to species becoming more specialized and having a narrower niche. Competition may lead to a reduction in reproductive capacity. 26

27 SPECIATION - the development of a new species ALLOPATRIC SPECIATION occurs due to GEOGRAPHIC ISOLATION whereby a sub-population becomes separated from the main population and can no longer share genes with it. The new population evolves independently of the first, creating a new species. 27

28 SYMPATRIC SPECIATION Organisms continue to live in the same place but become isolated by some other means. ie: Some fern species have doubled the number of chromosomes they have. This prevents them from breeding with the population from which they originally came and effectively creates a new species. ie: Two species of tree frogs have different mating calls. One species has twice the number of chromosomes. 28

29 Hyra chrysoscelis Hyra versicolor H. Chrysoscelis has the normal # of chromosomes H. Versicolor has double the normal # The difference in mating calls is a form of behavioral isolation and keeps each species isolated 29

30 POPULATION DIVERGENCE Once isolation occurs, the two populations begin to diverge (separate) due to: GENETIC DRIFT - chance events that cause genes to be lost from a population SELECTION PRESSURE - the selection pressures on the two populations are different BOTTLENECK EFFECT in a small population some genotypes are lost, survivors have fewer mutations available FOUNDER EFFECT when a small number of individuals determine 100% of future generations traits 30

31 TYPES OF SELECTION DIRECTIONAL SELECTION STABILIZING SELECTION DISRUPTIVE SELECTION 31

32 TYPES OF SELECTION 32

33 TYPES OF SELECTION 33

34 DIRECTIONAL SELECTION - one trait is being favored and the other is being eliminated so the population shifts toward one trait ie: giraffes that have long necks are favored 34

35 Stabilizing selection - range of a trait is narrowed 35

36 DISRUPTIVE SELECTION - traits diverge toward the two extremes 36

37 EVOLUTION IS STILL AT WORK In the Galapagos Islands, scientists have documented a change in the shape of finch beaks in just the past twenty years. When plants that made large seeds died due to a drought and only small seeds were available as food, the birds who had a beak shape suitable for eating small seeds survived and reproduced, and birds with beaks suited to eating large seeds died out. 37

38 TAXONOMY TAXONOMY is the study of organisms and their evolutionary relationships. It traces how organisms have descended from common ancestors. Scientists assign every organism a Genus and species name (A BINOMIAL) so that everyone can refer to a particular organism accurately. ie: Organisms are then organized into higher taxonomic categories such as kingdoms, etc. 38

39 THE SIX KINGDOMS Kingdom Phylum Class Order Family Genus Species 39

40 SPECIES INTERACTIONS - COMPETITION INTRASPECIFIC COMPETITION - Competition among members of the same species Competition is reduced if: - young disperse - animal defends a territory - adults and juveniles occupy different niches INTERSPECIFIC COMPETITION - competition between members of different species 40

41 INTRASPECIFIC COMPETITION Sage bush competing for space, water, light 41

42 INTERSPECIFIC COMPETITION Different warblers feed on insects at different areas of the forest. 42

43 SPECIES INTERACTIONS - PREDATION PREDATOR is any organism that feeds directly on another organism, whether or not it kills the prey. ie: a parasite feeds on an organism but does not kill it, Predation influences predators & prey Affects life cycle of both predators & prey Causes specialization in obtaining food Evolution of body forms/behavior for escape and successful predation 43

44 SPECIES INTERACTIONS - PREDATION PREDATOR-MEDIATED COMPETITION - one species may be the best competitor in a given location, but predators may reduce its abundance and allow the weaker competitor to increase its numbers. ie: White tail deer outcompete mule deer. Wolves begin to prey on high populations of white tail deer allowing mule deer to increase in number. 44

45 ADAPTATIONS TO AVOID PREDATION As predators become more efficient, the prey evolve defenses (thorns, toxic chemicals, etc.). Over time predator and prey evolve in response to one another (COEVOLUTION). Cheetah is faster, the antelope get faster Camouflage - prey & predator both use it! Prey in groups (flocks,herds,schools) predator grabs the least fit 45

46 ADAPTATIONS TO AVOID PREDATION Species with chemical defenses often evolve warning coloration. Harmless species mimic the warning coloration of harmful species to gain protection (BATESIAN MIMICRY). Two harmful species evolve to look alike (MULLERIAN MIMICRY). 46

47 BATESIAN MIMICRY 47

48 MULLERIAN MIMICRY 48

49 SPECIES INTERACTIONS - SYMBIOSIS SYMBIOSIS two or more species live intimately together with their fates linked. MUTUALISM + + COMMENSALISM + o PARASITISM + - AMENALISM - o 49

50 SYMBIOSIS - MUTUALISM MUTUALISM both benefit from each other ie: a fungus and an alga combine to make a lichen sea anemone and clownfish cohabitate oxpecker and impala 50

51 SYMBIOSIS - COMMENSALISM COMMENSALISM - one species benefits while the other neither benefits nor is harmed. ie: birds nest in a cactus remora on a shark epiphytic orchids on a tree 51

52 SYMBIOSIS - PARASITISM PARASITISM (also a form of predation) it can be considered a form of symbiosis because of the dependency of the parasite on its host. Flea on a dog Tapeworm in an intestine Mosquito drawing blood 52

53 SYMBIOSIS - AMENSALISM AMENSALISM is the interaction between species where on suffers and the other is unaffected. Black walnuts release chemicals that kill other plants near it Penicillium mold releases chemicals that kill bacteria 53

54 KEYSTONE SPECIES KEYSTONE SPECIES plays a critical role in a biological community that is out of proportion to its abundance. ie: In the tropics, figs bear fruit year round. In the dry season, this is the only food available for many species. If figs were removed from the forest, many fruit-eating animals would disappear and this in turn would affect many other plants that depend upon them for pollination or seed dispersal. So, the fig is key to the survival of the community. 54

55 KEYSTONE SPECIES Sea otters in the Kelp Forest prey on sea urchins. If sea otters disappear the urchins will devour the kelp and the forest and the 1000 s of species would be lost. 55

56 REMEMBER... COMMUNITY PROPERTIES Primary Productivity is the rate of biomass production. Used as an indication of the rate of solar energy conversion to chemical energy (bonds in glucose) Net Primary Productivity - energy left after respiration of plants Tropical forests, coral reefs, and estuaries have high levels of productivity. (they have large amounts of light, high temperature, abundant nutrients, and water) 56

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58 ABUNDANCE vs DIVERSITY ABUNDANCE - total number of organisms in a community DIVERSITY - number of different species, ecological niches, or genetic variation Abundance of a particular species is often inversely related to community diversity. As a general rule, diversity decreases and abundance within species increases when moving from the equator to the poles. 58

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60 COMMUNITY & ECOLOGICAL STRUCTURE patterns of spatial distribution of individuals & populations within a community 1. RANDOM DISTRIBUTION Species live wherever resources are available 60

61 COMMUNITY STRUCTURE 2. CLUSTERED/CLUMPED DISTRIBUTION for protection, mutual assistance, reproduction, access to resources 61

62 COMMUNITY DISTRIBUTION Distribution can be vertical and/or horizontal. 62

63 COMMUNITY STRUCTURE 3. UNIFORM DISTRIBUTION often the result of competition or territoriality 63

64 COMPLEXITY AND CONNECTEDNESS COMPLEXITY - number of species at each trophic level and the number of trophic levels in a community Diverse community may not be complex if all species are clustered in a few trophic levels. Highly interconnected community may have many trophic levels, some of which can be compartmentalized. 64

65 RESILIENCE AND STABILITY CONSTANCY - Lack of fluctuation in composition or function INERTIA - Resistance to perturbation ability to maintain a state of equilibrium RENEWAL - Ability to repair damage after a disturbance MacArthur proposed that complex, interconnected communities would be more stable and resilient in the face of disturbance. - Some studies have supported this idea while others have not. 65

66 EDGE EFFECTS - important aspect of community structure is the boundary between one habitat and others 66

67 ECOTONES - boundaries between adjacent communities Sharp boundaries - closed communities Indistinct boundaries - open communities 67

68 COMMUNITIES IN TRANSITION ECOLOGICAL SUCCESSION PRIMARY SUCCESSION - A community begins to develop on a site previously unoccupied by living organisms. Example: A lava flow creates a new land area that is colonized. The first colonists are termed PIONEER SPECIES. (lichens) SECONDARY SUCCESSION - an existing community is disrupted and a new one subsequently develops at the site CLIMAX COMMUNITY - community that develops last and remains the longest 68

69 COMMUNITIES IN TRANSITION ECOLOGICAL SUCCESSION FACILITATION when one species modifies the environment making it more suitable for another species - ie: lichens create soil INHIBITION when one species modifies the environment making it unsuitable for others - ie: pines make soil acidic to other plants TOLERANCE when species are unaffected by each other - Different herbaceous plants in a field 69

70 PRIMARY SUCCESSION Always starts with bare rock! ie: lava flow, landslides, sand bar 70

71 SECONDARY SUCCESSION Has topsoil already present! 71

72 AQUATIC SUCCESSION Ponds, lakes, and marshes will be converted to land over time. 72

73 DISTURBANCES a DISTURBANCE is any force that disrupts established patterns of species diversity and abundance, community structure, or community properties ie: storms, fires, logging. Disturbance tends to disrupt the superior competitors the most and allows less competitive species to persist. Some landscapes never reach a climax community because they are characterized by periodic disturbances (such as wildfires) and are made up of DISTURBANCE-ADAPTED SPECIES. 73

74 INTRODUCED SPECIES & DISTURBANCE If introduced species prey upon or out-compete native populations, the nature of the community may be altered. Introduction of rats, cats, goats and pigs where European sailing ships landed Introduction of exotic species to solve problems caused by previous introductions - Mongoose and rats in Caribbean - Cane toad in Australia Unintentional introduction - Zebra Mussels, Asian longhorn beetle 74

75 Introduced species in aquatic ecosystems come from ballast water in ships 75

76 Mongoose Cane Toad Goats Zebra Mussels 76