chapter 53 population ecology. 53.1 dynamic biological processes influence population density,...

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  • Slide 1
  • CHAPTER 53 POPULATION ECOLOGY
  • Slide 2
  • 53.1 DYNAMIC BIOLOGICAL PROCESSES INFLUENCE POPULATION DENSITY, DISPERSION, AND DEMOGRAPHICS
  • Slide 3
  • POPULATION Population- a group of individuals of a single species living in the same general area Three fundamental characteristics of a population Density Dispersion Demographics
  • Slide 4
  • DENSITY AND DISPERSION Scientists have begun investigating the boundaries of a population. They may be natural or arbitrarily defined Density the number of individuals per unit area or volume Dispersion the pattern of spacing among individuals within the boundaries of the population
  • Slide 5
  • DENSITY Almost impossible to actually count the number of individuals Some ecologists will estimate and extrapolate Mark-Recapture method Density is not a static property Immigration- the movement of organisms into an area Emigration- the movement of organisms out of the area
  • Slide 6
  • PATTERNS OF DISPERSION Clumped sea stars grouping together where food is abundant Uniform penguins maintaining almost equal spacing due to aggressive interactions between neighbors Random dandelions growing wherever the seeds land and germinate
  • Slide 7
  • (a) Clumped (b) Uniform (c) Random
  • Slide 8
  • DEMOGRAPHICS Demography the study of vital statistics of populations and how they change over time Life tables Survivorship curves
  • Slide 9
  • LIFE TABLES Age-specific summaries of the survival pattern of a population Best way to construct one is to follow the fate of a cohort from birth until death A group of individuals of the same age
  • Slide 10
  • SURVIVORSHIP CURVES A graphing method of representing the data in a life table Three different types of patterns Type I- flat to start then drops steeply Humans and other mammals Type II steady decline Squirrels Type III drops sharply at the start Oysters
  • Slide 11
  • Survivorship Curves 1,000 100 10 1 050100 II III Percentage of maximum life span Number of survivors (log scale) I
  • Slide 12
  • REPRODUCTIVE RATES Demographers typically ignore males and focus on females A reproductive table (fertility schedule) is an age specific summary of the reproductive rates in a population. Tallies the number of female offspring produced by each age group
  • Slide 13
  • 53.2- LIFE HISTORY TRAITS ARE PRODUCTS OF NATURAL SELECTION
  • Slide 14
  • Natural selection favors traits of organisms that allow them to survive longer and reproduce Life history- the trait that affects an organisms schedule of reproduction and survival Start of reproduction How often reproduction occurs Amount of offspring per reproduction cycle
  • Slide 15
  • EVOLUTION AND LIFE HISTORY DIVERSITY One-shot reproduction Semelparity- one big reproduction of offspring (big bang reproduction) Iteroparity- offspring over many years 2 critical factors: Survival rate of offspring Likelihood hood that adults will live to reproduce again
  • Slide 16
  • EVOLUTION AND LIFE HISTORY DIVERSITY Semelparity if offspring arent likely to survive long Iteroparity if the environment is favorable to the adults
  • Slide 17
  • TRADE-OFFS AND LIFE HISTORIES Natural selection cannot maximize all reproduction variables simultaneously Time, energy, and nutrients limit reproduction of organisms Trade-offs between survival and reproduction Selective pressures between number of offspring and size of offspring Parent care and learn through 1 st year makes an impact
  • Slide 18
  • 53.3- THE EXPONENTIAL MODEL DESCRIBES POPULATION GROWTH IN AN IDEALIZED, UNLIMITED ENVIRONMENT
  • Slide 19
  • Potential to expand if resources are right Reveals capacity of species for increase and conditions under which capacity may be expressed
  • Slide 20
  • PER CAPITA RATE OF INCREASE Population will increase with births and emigrations Populations will decrease with deaths and immigration Change in population= (birth + immigration) (deaths + emigrations)
  • Slide 21
  • PER CAPITA RATE OF INCREASE Per capita birth rate- number of offspring produced by an average member of the population Per capita death rate- expected number of deaths per a unity of time Most interested in the difference between the death and birth rates
  • Slide 22
  • PER CAPITA RATE OF INCREASE R=b-d R is the indication whether a given population is growing or declining Zero population growth (ZPG) the birth and death rates equal zero
  • Slide 23
  • EXPONENTIAL GROWTH Exponential population growth- population increase under ideal conditions J-shaped curved Can mean the introduction to a new environment Numbers that have been affected by a catastropic event
  • Slide 24
  • 53.4 THE LOGISTIC MODEL DESCRIBES HOW A POPULATION GROWS MORE SLOWLY AS IT NEARS ITS CARRY CAPACITY
  • Slide 25
  • Exponential growth model assumes that resources are unlimited Not the case in the real world Carrying capacity (K) the maximum population size that a particular environment can sustain
  • Slide 26
  • THE LOGISTIC GROWTH MODEL
  • Slide 27
  • 2,000 1,500 1,000 500 0 051015 Number of generations Population size (N) Exponential growth 1.0N = dN dt 1.0N = dN dt K = 1,500 Logistic growth 1,500 N 1,500
  • Slide 28
  • 1,000 800 600 400 200 0 051015 Time (days) Number of Paramecium/mL Number of Daphnia/50 mL 0 30 60 90 180 150 120 020406080100120140160 Time (days) (b) A Daphnia population in the lab(a) A Paramecium population in the lab
  • Slide 29
  • LOGISTIC MODEL AND REAL POPULATIONS The logistic model assumes that populations will adjust instantaneously This is not typically the case This will cause a population to temporarily overshoot the carrying capacity Allee effect- individuals may have a more difficult time surviving or reproducing if the population size is too small
  • Slide 30
  • LOGISTIC MODEL AND LIFE HISTORIES K-selection- density dependent Operates in populations living at a density near their carrying capacity R-selection- density independent Traits that maximize reproductive success in uncrowded environments
  • Slide 31
  • 53.5 MANY FACTORS THAT REGULATE POPULATION GROWTH ARE DENSITY DEPENDENT
  • Slide 32
  • POPULATION CHANGE AND POPULATION DENSITY Density independent populations will have birth and death rates that will not change with density Density dependent populations will have birth and death rates that will rise and fall with density
  • Slide 33
  • DENSITY-DEPENDENT POPULATION REGULATION Without some type of negative feedback between population density and the rates of birth and death, a population will never stop growing. Competition for resources Increasing population density competing for declining nutrients will lead to a lower birth rate Toxic Wastes The accumulation of toxic waste can effect population size Intrinsic Factors In some cases the physiological factors rather than the environmental factors will influence the population size
  • Slide 34
  • CONTINUED Territoriality Territory spaces becomes a resource in which individuals compete for. Disease If the transmission rate of a certain disease depends on the crowding in a population, density will be effected Predation A predator encounters and captures more food as the density of the prey increases
  • Slide 35
  • (a) Cheetah marking its territory (b) Gannets Territoriality
  • Slide 36
  • WolvesMoose 2,500 2,000 1,500 1,000 500 Number of moose 0 Number of wolves 50 40 30 20 10 0 195519651975198519952005 Year Predation
  • Slide 37
  • POPULATION DYNAMICS Focuses on the complex interactions between the biotic and abiotic factors that cause variation in the size of populations Populations of large mammals were once thought to remain stable over time, this is not the case
  • Slide 38
  • IMMIGRATION, EMIGRATION, AND METAPOPULATIONS Immigration and emigration can also affect populations Metapopulation- a group of spatially separated populations of one species that interact through immigration and emigration Local populations can be thought of as occupying small patches of suitable environment within a sea of unsuitable habitat Patches will vary in size, quality, and isolation from other patches There are many factors that will influence how patches interact
  • Slide 39
  • CHAPTER 54 COMMUNITY ECOLOGY
  • Slide 40
  • COMMUNITY INTERACTIONS ARE CLASSIFIED BY WHETHER THEY HELP, HARM, OR HAVE NO EFFECT ON THE SPECIES INVOLVED 54.1
  • Slide 41
  • COMPETITION Interspecific competition has a negative effect on the survival and reproduction of the predator population and a negative effect on that of the prey population. Occurs when individuals of different species compete for a resource that limits their growth and survival. ie. Weeds compete from soil nutrients and water. Grasshoppers vs. bison for grass they both eat.
  • Slide 42
  • COMPETITION: COMPETITIVE EXCLUSION Two species competing for the same limit

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