POPULATION STUDIES. Population ecology is the study of the factors affecting the sizes of different populations.

Transcription

1 POPULATION STUDIES Population ecology is the study of the factors affecting the sizes of different populations.

2 Definitions Population: group of individuals same species living in same definable area can undergo random breeding reproductively isolated from other individuals of the same species in other habitats

3 Definitions continued Species A group of individuals with similar characteristic that can breed amongst themselves and produce viable offspring Individual A single organism capable of independent existance

4 Definitions continued Different populations interacting with one another make up a community. An ecosystem refers to the interactions between a community of organisms (as the biotic factors) and the abiotic or physical factors in that locality.

5 Definitions continued The particular combination of abiotic and biotic factors that determine where a species can survive and reproduce is called that species ecological niche.

6 Definitions Population size number of individuals in a population

7 Definitions Population density number of individuals per unit area

8 Population parameters Variables affecting the numbers of individuals in a population: Natality Birth rate Mortality Death rate Immigration number of individuals entering a habitat Emigration number of individuals leaving a habitat

9 Natality 1. The natural ability of a population to increase as shown by the birth rate in animals and the production of seeds in plants. 2. It is the percentage increase of the population per unit time. 3. In humans it is expressed as the number of births per 1000 persons per year. 4. Different organisms have different numbers of offspring.

10 R strategy organisms e.g. fish, insects, frogs, bacteria. These organisms: Produce large numbers of offspring Lack parental care offspring are small Only a few of the offspring survive (so there is a high juvenile mortality)

11 K-strategy organisms e.g. birds and mammals These organisms: produce only a few offspring and as they have a high level of parental care, the young have a good chance of survival.

12

13 Mortality This is the rate at which individuals of a population die. For humans this is the number of deaths per 1000 individuals per year.

14 Survivorship Curves

15 Survivorship Curves Type I - Convex survivorship curve: most of the offspring survive to adulthood it is mostly the old individuals that die This curve is found in species that show a K-strategy of natality with a high degree of parental care e.g. mammals and birds. Type III - Concave survivorship curve: few offspring reach adulthood it is mostly the young individuals that die and as the offspring age, there is a decrease in mortality This curve is found in species that show a r-strategy of natality with a low degree of parental care e.g. fish and amphibians. Type II - Straight line survivorship curve: young individuals are as likely to die as old ones Some songbirds and Hydra show this type of survivorship curve.

16 Immigration refers to individuals entering an area from another area. This occurs especially when a population colonises a favourable new habitat. Emigration refers to individuals leaving an area. This occurs especially when an area becomes overpopulated, resulting in a lack of food or space.

17

18 Closed population: the only factors affecting population size are natality and mortality. There is no immigration or emigration. Open population: factors affecting population size are natality, mortality, immigration and emigration.

19 Population growth births exceed deaths and / or immigration exceeds emigration Increase in numbers, or density or biomass

20 Population growth curves 1. Geometric / exponential growth the rate of increase increases with time J-shaped curve increases to extinction phase an example of an organism that shows this type of population growth is bacteria

21

22 Logistic growth

23

24 CARRYING CAPACITY Carrying capacity is defined as the maximum number of individuals (population size) that the environment can support over a relatively long period of time. The carrying capacity of any environment is determined by the limiting factors that exist in that environment (environmental resistance) Any environment with fewer resources will have a lower carrying capacity than one that has greater resources for the population under study.

25 As the density of the individuals increases, the environmental resistance increases and limiting factors begin to affect the rate of population growth. Environmental resistance is made up of the following factors: increased competition for food and space between individuals an increase in the number of parasites and predators in territorial species, all the territories being occupied toxic waste accumulating and poisoning individuals

26 Estimation of population size Direct methods: every individual is counted Indirect methods: a segment of the population is counted a formula is applied / calculation is done the population size is estimated

27 Direct methods Census: Humans are counted by a census. Every person is counted.

28 Direct methods Aerial photography: aerial photographs taken of whole area. Photographs are patched together and the specimens counted. Limitations: type of vegetation must be considered, type of animal must be considered (size and speed of movement), type of terrain must be considered. Census/6.png

29 Indirect techniques Quadrat method of sampling All individuals in sample area of known size (called a quadrat) are counted. Repeated for a number of quadrats. Average number per quadrat calculated. Formula: Population size = average no. in quadrat x habitat size quadrat size

30 Total area = 10m x 8m =80 m2 Quadrat size = 2m x 1m = 2m2 2m 1m =15 15/6 = 2.8 starfish per sample Number of starfish 2.5 x 80m2 2m2 = 100 starfish

31 Population size = average no. in quadrat x habitat size quadrat size Table of number of crabs counted in 6 quadrats in a marine estuary Quadrat number Number of crabs Average 4 As the quadrats were 1 m 2 in size, then in the entire estuary of 200 m 2, the number of crabs is estimated as follows: population size = 4 x 200 m 2 1 m 2 = 800 crabs

32 Quadrat method Accuracy depends on: Random distribution of quadrats Large enough sample size taken (enough repeats) Calculating the average correctly

33 2. Mark-recapture technique Catch a sample of organisms of the species being counted (sample 1), count, mark and release. Allow time to spread out in population Catch a second sample (sample 2). Count whole sample as well as the number in second sample that are marked. Apply formula (Petersen s index) P = M x C R Where P = estimated population size M = number in first sample C = number in second sample R = number marked in second sample Repeat 3 times, calculate an average.

34 Mark recapture Precautions to take to ensure accuracy: a. The marking must not affect the animal. b. The mark must not wear off between counts. c. The individual must mix with the rest of the population after the marking. d. The population should be closed. e. There are no births or deaths during the time of the investigation. f. The chance of an animal being captured must not change due to age or experience during the time of the investigation.

35 POPULATION REGULATION Factors which are responsible for regulating the size of a population

36 POPULATION REGULATION CARRYING CAPACITY: The carrying capacity of an environment is a major factor regulating the size of populations.

37 If the population far exceeds the carrying capacity, the habitat will deteriorate, causing degradation. This will lead to a lowering of the carrying capacity, which will lead to even greater environmental resistance. This will causes a decrease in population size. Eventually the habitat will not be able to support the population, which will become extinct.

38 Population regulation Environmental resistance is defined as: All the biotic and abiotic factors combining to limit the growth of a population.

39 Environmental resistance

40 Environmental resistance factors / limiting factors: Resources e.g. food, water, oxygen Physical conditions e.g. climate, living space Biotic factors e.g. predation, competition, disease These may case population growth to slow down or decrease

41 ENVIRONMENTAL RESISTANCE TWO TYPES: A. DENSITY INDEPENDENT B. DENSITY DEPENDENT

42 Density independent parameters: These affect a population equally regardless of the population density. These factors can cause large fluctuations in population size. o Climatic factors / weather e.g. rainfall, temperature (severe winter) o Natural disasters e.g. drought floods earthquakes volcanoes

43 mage/chinaearthquake02.jpg nd/images/mozambique_floods.jpg

44 Density- dependent parameters: These affect a population less when a population is low and more when the population is high and more dense. In general, density-dependent factors are biological factors,

45 Density-dependent parameters: The more dense a population the greater their effect. These include: Food Space Disease Shelter Predation Competition

46 Density-dependent factors These factors prevent overpopulation and result in stable populations with slight fluctuations. These factors are affected by changes in the population they are acting on - i.e. they are negative - feedback mechanisms.

47 Space and shelter Food DENSITY DEPENDENT FACTORS Disease Water

48 The higher the population, the more dense the population distribution, the easier it is for disease to spread from an infected organism to an uninfected organism.

49 Predator prey relationships Predator an organism that catches and kills live prey for food

50 Predator-prey graph

51 Predator-prey relationship: Lion and Zebra s04/lionchase.jpg ategorized/lion_eating_zebra.jpg

52 Predator-prey relationship: Great White shark and seal

53 Competition Competition Organisms often require the same resources, such as water, food, space or sunlight. If there is a limited supply of one or more of these resources, it may mean that the needs of both organisms cannot be satisfied; the two organisms will then have to compete with one another for the resource or resources.

54 Intraspecific competition between individuals of the same species for food, space, reproductive partners and other share resources May lead to: territoriality hierarchical behaviour

55 Survival of the fittest This type of competition is considered to be an important force causing evolutionary change. Competition for resources leads to survival of the fittest. In many bird species males fight each other for ownership of territories, where the resources needed for survival and mating are available. In plants the nature of the competing is different. For example, plants that can grow rapidly and shade other plants of the same species are more likely to survive.

56 Dominance and submissive behaviour

57 Interspecific competition competition that occurs between individuals of different species for the resources they have in common

58 Interspecific competition Lion and hyena compete for the same food source

59 Resource Partitioning Species coexist in ecosystems to the extent that they share resources. To avoid one species dying out completely, co-existing species partition or divide certain resources so that one species does not out-compete the other. Resource partitioning minimises competition between similar species.

60 Resource partitioning When two species partition /divide a resource based on behavioural or morphological (physical) variation.

61 Resource partitioning stratification in forests

62 Resource partitioning differential grazing Zebras eat the tall, coarse grass and open up the grass layer for the wildebeest that follow. After the zebras eat, the wildebeests eat the shorter grass left behind.

63 CO - EXISTING PREDATORS Leopards have adapted to live alongside other predators e.g. lion, by hunting for different types of prey and by avoiding areas frequented by them.

64 Impact of food webs on populations The website shows the effect of increasing or decreasing any organism in a food web.

65 Food webs: interconnected and interdependent food chains

66 Survival strategies These are any behaviours that are used to help the species survive. territoriality natality altruism ritual displays hierarchies with dominance and submissiveness

67 Social organization as a technique to enhance survival Flocks or herds Some animals live in herds or flocks to as a predator avoidance strategy. An example of animal that uses this method successfully to avoid predation is the zebra.

68 Stripes in a zebra herd The stripes are thought to confuse predators by motion dazzle a group of zebras standing or moving close together may appear as one large mass of flickering stripes, making it more difficult for the lion to pick out a target. It is difficult to tell where one zebra ends and another begins. If a predator such as a lion can't pick out an individual zebra to zero in on for a kill, it's less likely to succeed in bringing one down for a meal.

69 A confusion of stripes in a zebra herd From:

70 Other benefits of living in a herd: There is a great chance a predator will attack another member of the herd and leave the majority alone. The large size of the herd might scare away a foe who would attack a lone straggler. The larger the group, the lower the level of individual vigilance and the greater the sum of collective vigilance. Individual animals can spend more time eating rather than watching out for predators, even though the collective as a whole is safer. Not all members of the herd are equally attentive, which is one of the advantages of this social grouping. Researchers have found that the individuals at the perimeter of herds are more vigilant than those in the centre.

71 Hunting in packs and / or having a dominant breeding pair, e.g. wild dogs

72 Wild dogs - hunting Hunt in groups Run their prey down and tire them out Have a hunting strategy Communicate while hunting Most efficient hunters Eat their prey very quickly and return to the den Food remains in the stomach until they reach the den. Hunters regurgitate the food to share with the pups and adults who remain behind including sick and injured members

73 Dominance and submissiveness Alpha male and female breed, all others share in caring for, guarding and feeding the young inance-games-wild-dog-play-fight.jpg

74 Division of labour e.g. termites Termite nest Termite castes images/trinervitermes-x-section.gif m/castes.gif

75 Termites Termites display a caste system with division of labour. The major castes in the colony are the reproductive, soldier and worker castes. The members of each caste are structurally different with specific functions to perform to ensure the colony's survival and maintenance.

76 Termites metamorphose through egg to nymph to adult. After moulting several times, the young nymphs differentiate into the different castes. This may take several months, depending upon food availability, temperature, and the colony's vigour.

77 Soldiers: Large, dark, hard head with powerful jaws (mandibles). The head and the mandibles are used to defend the colony against predators, usually ants. Wingless and usually lack eyes. Can be either male or female, but they lack fully developed reproductive organs. Jaws are so enlarged that they cannot feed themselves, but instead, are fed by workers Main job is defence against enemies such as ants that prey on termites From

78 Workers: Pale in colour, soft-bodied Wingless and usually lack eyes Can be either male or female, but lack fully developed reproductive organs Hardened mandibles and mouthparts adapted for chewing Feed all the other members of the colony (reproductives, soldiers, and young), collect food, groom other colony members, and construct and repair the nest Workers need high humidity to survive and will carry mud up into the wood where feeding to maintain a 97% relative humidity.

79 Worker termites

80 Reproductives The main reproductive have wings at one stage in their life and are generally the only termites with well-developed eyes Their tasks include reproduction, dispersal, and colony formation Winged Reproductives A termite queen warts-pest-control-castes2.gif

81 In a typical termite colony, the king and queen are the only active reproductives and they perform no other function. They are fed by the other termites, and some have lived up to 25 years. A mature queen can lay thousands of eggs each year up to a thousand a day. In many termite species the queen is monogamous. A queen and king termite, along with a few workers From:

82 The king termite assists the queen in creating and attending to the colony during its initial formation. He will continue to mate throughout his life to help increase the colony size. As the queen ages, her reproductive capacity declines, and the colony may then select supplementary queens from the various developmental stages of reproductives to assist the queen and king by laying eggs. These reproductives never go on a colonising flight.

83

84 Colonising flights - swarming A "swarm" is a group of winged reproductive adults that leave their nest to establish a new colony. Swarming occurs when a colony reaches a certain size. Emergence is stimulated when temperature and moisture conditions are favourable, usually on warm days following rainfall.

85 A swarm of termites From:

86 A very small percentage of swarming termites survive to initiate new colonies. Many are eaten by predators such as other insects and birds. The king and queen care for the first generation of the new colony on their own until they've raised enough workers to take over the job. Workers expand the nest, and the queen's abdomen enlarges so she can lay more eggs. It takes two to four years for the colony to mature, and then the cycle starts again with a new set of alates swarming to form new colonies.

87 Termite colony ml

88 Ecological succession Ecological succession is the gradual process of change in the species structure of an ecological community over time.

89 Primary succession The establishment of a community where none existed before, as would happen on bare land, such as rock exposed by a retreating glacier or a recent larval deposition. It can also be found in areas where volcanic eruptions have occurred, leaving solid rock/no soil for plant succession to continue from before the eruption. The rock must be broken down to form soil again.

90 Primary succession (1) The establishment of a community where none existed before, as would happen on bare land, such as rock exposed by a retreating glacier or a recent larval deposition. The first organisms to establish themselves (or colonize) the new environment are referred to as PIONEER SPECIES. These species have adaptations that enable them to survive in harsh environments where very high or very low temperatures are common, and dehydration (drying out) occurs.

91 Primary succession (2) As generations of pioneers live and die, they help to build and improve the soil for the next group of plants

92 Primary succession (2) As generations of pioneers live and die, they help to build and improve the soil. Ecological niches are created for other species and these replace of the pioneer species.

93 Primary succession (2) As generations of pioneers live and die, they help to build and improve the soil. Ecological niches are created for other species and these replace of the pioneer species. As the following species are slightly larger and more specialised, they grow over the top original pioneers, competing with them for sunlight, and winning.

94 Primary succession (2) As generations of pioneers live and die, they help to build and improve the soil. Ecological niches are created for other species and these replace of the pioneer species. As the following species are slightly larger and more specialised, they grow over the top original pioneers, competing with them for sunlight, and winning. Insects, spiders, and other animals become part of the community as their energy requirements can be met by species that are already there.

95 Primary succession (2) As generations of pioneers live and die, they help to build and improve the soil. Ecological niches are created for other species and these replace of the pioneer species. As the following species are slightly larger and more specialised, they grow over the top original pioneers, competing with them for sunlight, and winning. Insects, spiders, and other animals become part of the community as their energy requirements can be met by species that are already there. Gradually, as the ecosystem develops and supplies of water and nutrients become more predictable, grasses and other small plants invade the community and are available for herbivores, large and small.

96 Primary succession (3) As the process continues, a group of species that tends to dominate the community and persist through time is gradually assembled the climax community.

97 Primary succession (3) As the process continues, a group of species that tends to dominate the community and persist through time is gradually assembled the climax community. The nature of the climax community depends on the abiotic factors including the climate of the area.

98 Primary succession (3) As the process continues, a group of species that tends to dominate the community and persist through time is gradually assembled the climax community. The nature of the climax community depends on the abiotic factors including the climate of the area. Climax communities may change if conditions change.

99 ma.edu/biol201/file s/succession.gif

100 Primary seccession on a glacial moraine interactive:

101 Secondary succession (1) Established communities are periodically altered by natural forces, such as floods, fires, hurricanes, and earthquakes.

102 Secondary succession (1) Established communities are periodically altered by natural forces, such as floods, fires, hurricanes, and earthquakes. After a disturbance destroys a community, the forces that initially acted to build the community take over again. A new sequence of community development occurs one that is called secondary succession.

103 Secondary succession (2) Soil is present, as well as seeds of plants brought in by wind and animals etc. As was the case during the initial development of the community, early colonizers, which possess adaptations that allow them to establish a population quickly, are particularly common at first.

104 Secondary succession (2) As was the case during the initial development of the community, early colonizers, which possess adaptations that allow them to establish a population quickly, are particularly common at first. Later-arriving species often display the characteristics of K-strategy species (slow development; delayed reproduction; large body size, repeated reproduction; fewer, larger offspring; long lifespan).

105 The cycle of secondary succession in an ecosystem

106 Secondary succession (3) Sometimes succession may not lead to a climax community. For example, many grasslands are maintained by a combination of grazing and fire. In the absence of these factors, grassland usually develops into shrub-land and then into forest. When these factors are present, they create a permanent grassland as an end point for a community. The succession of species in different areas can have different end points, depending on the particular environmental conditions and the kinds of plants and animals.

107 Chapter 4 Population Ecology 4.2 Human Population Human Population Growth The study of human population size, density, distribution, movement, and birth and death rates is demography.

108 Chapter 4 Population Ecology 4.2 Human Population Technological Advances For thousands of years, environmental conditions kept the size of the human population at a relatively constant number below the environment s carrying capacity. Humans have learned to alter the environment in ways that appear to have changed its carrying capacity.

109 Chapter 4 Population Ecology 4.2 Human Population Human Population Growth Rate Although the human population is still growing, the rate of its growth has slowed.

110 Chapter 4 Population Ecology 4.2 Human Population Trends in Human Population Growth Population trends can be altered by events such as disease and war. Human population growth is not the same in all countries.

111 Chapter 4 Population Ecology

112 Chapter 4 Population Ecology 4.2 Human Population Zero Population Growth Zero population growth (ZPG) occurs when the birthrate equals the death rate. The age structure eventually should be more balanced with numbers at prereproductive, reproductive, and postreproductive ages being approximately equal.

113 Chapter 4 Population Ecology 4.2 Human Population Age Structure A population s age structure is the number of males and females in each of three age groups: pre-reproductive stage, reproductive stage, and postreproductive stage.

114 Chapter 4 Population Ecology 4.2 Human Population Human Carrying Capacity Scientists are concerned about the human population reaching or exceeding the carrying capacity. An important factor is the amount of resources from the biosphere that are used by each person.