1003-1014 pg pop ecol. Chapter 51 Introduction to Ecology: Population Ecology
ecology - the study of how living organisms and the physical environment interact in an immense and complicated web of relationships; broadest field of biology. -interactions between organisms - those between organism and their nonliving, physical environment, ; include precipitation, pH, chemical nutrients, wind - a scientific discipline with ties to ecology, focuses on how humans interact with the environment - a group consisting of members of the same species that live together in a prescribed area at the same time.
biotic factors abiotic factors
environmental science population
FEATURES OF POPULATIONS 1. define population density and dispersion, and describe the main types of population dispersion -Characteristics of populations are population density, population dispersion, birth and death rates, growth rates, survivorship, and age structure. population ecology -considers both the number of individuals of a particular species that are found in an area and the dynamics of the population population dynamics -the study of changes in population-how and why those numbers increase or decrease over time. Density and dispersion are important features of populations population density -is the number of individuals of a species per unity of area or volume at a given time dispersion -populations often exhibits characteristic patterns of dispersion or SPACING. come in clumped; uniform, or random dispersion clumped dispersion - aka aggregated distribution or aka patchiness; is most common spacing; occurs when indivudauls are concentrated in specific parts of habitat. ; often results from clumped natural resources, and other reasons such as asexual reproduction, limited seed dispersal, and social reasons; advantage is less likely hood to be eaten by predator uniform dispersion -occurs when individuals are more evenly spaced than would be expected from a random occupation of a given habitat. ex: nesting birds evenly spaced out on land due to TERRITORY; also occurs when competition severe random dispersion -occurs when individuals in a population are spaced throughout an area in a manner that is unrelated to
the presence of others. ; least common; ex: flour beetle larvae in flour; *Sand pines are fire adapted. At first are uniform due to competing for sunlight; next when fire occurs, they release seeds, then after, they are either random or slightly clumped; then become uniform again due to competition Review -What is the difference between population density and dispersion? -What are some biological advantages of a clumped dispersion? What are some disadvantages? CHANGES IN POPULATION SIZE 2. explain the four factors (natality, mortality, immigration, and emigration) that produce changes in population 3. define intrinsic rate of increase and carrying capacity, and explain the difference between J-shaped and S-shaped growth curves. *on global scale population change is caused by two factors Natality - the average per capita birth rate mortality -the average per capita death rate (capita means individual) delta N is change in the number of individuals in the population delta t is the change in time, b is the natality, d the mortality (1) delta N/ delta t = N (b-d) Growth rate (r) -is the rate of change (increase or decrease) of a population on a per capita basis as expressed in equation 2.
(2) r = b-d Thus, ex: There are 10,000. people. 200 are born every year. 100 die every year. Thus, b is (200/10000) or 20/1000 10/1000 = 0.01 or 1 % (check pg 1006) *in equation (3), the instantaneous growth rate (dN/dt) is given. (3) dN/dt = rN where N is the existing population, r is per capita growth rate, t is the time, Dispersal affects the growth rate in some populations dispersal -the movement of individuals among populations; is considered when examining populations on a local scale; two types of dispersal are immigration and emigration immigration -occurs when individuals enter a population and thus increase its size emigration -occurs when individuals leave a population and thus decrease its size. *for equation 4, r is growth rate, birth rate is b, death rate is d, immigration rate is I, and emigration rate is e on a per capita basis (4) r = (b-d) + (i-e)
Thus ex: population is 10,000. Has 200 births, 100 deaths, 10 immigrants, 100 emigrants in year r = (20/1000 10/1000) + (1/1000-10/1000) Each population has a characteristic intrinsic rate of increase intrinsic rate of increase -rmax , maximum rate at which a population can increase; such as when conditions are ideal, resources are high and population density is low; *several factors affect this; 1. age at which reproduction begins 2. fraction of life span which individual is capable of reproducing 3. number of reproductive periods per lifetime 4. number of reproductive periods per lifetime 5. and the number of offspring produced *generally, large animals have low intrinsic rates of increase and microbes have HUGE exponential population growth -has a J shape; is the accelerating population growth rate that occurs when optimal conditions allow a constant per capita growth rate No population can increase exponentially indefinitely *if happens, it's in short amount of time; environment sets limits; carrying capacity (K) -represents the largest population that can be maintained for an indefinite period by a particular environment, assuming no changes occur in environ *in nature K is dynamic an d always changing logistic population growth - S shaped growth curve; rate slows down as approaches K; happens when studied over long period of time. model describes small population increasing to capped large population; S curve is oversimplification but has been observed *logistic equation is: (5) dN/dt = rN[(K-N)/K] *is similar to equation three but [(K-N)/K] reflects a decline in growth as a population size approaches its carrying capacity population crash -when population overshoots K, an abrupt decline from high to low density occurs; common in bacteria *ex: at first 25 reindeer introduced; grew to 2000; ate all the food and wiped out vegetation; winter came and deer starved; population plummeted to Thus 8; now carrying capacity has been reduced until vegetation starts to grow again. Review -What effect does each og the following have on population size? a. natality, b, mortality, c. immigration, d. emigration -How does a J shaped population growth curve differ from an S-shaped curve in terms of intrinsic rate of increase and carrying capacity?
-What would be the main difference between graphs representing long term growth of two populations of bacteria cultured in a test tubes, one in which the nutrient medium is replenished, and the other in which it is not replenished? FACTORS INFLUECING POPULATION SIZE 4. contrast the influences of density-dependent and density-independent factors on population size and give examples of each. *two categories affecting population size: density-dependent factors and densityindependent factors Density-dependent factors regulate population size density-dependent factor -environmental factor affecting a population; if a change in population density alters how factor affect population; Are an excellent example of a negative feedback system; examples are predation, disease, and competition negative feedback system - (regulates) Density-dependent factors may explain what makes certain populations fluctuate cyclically over time "boom or bust" populations Competition is an important density-dependent factor competition -interaction between two or more individuals that attempt to use the same essential resources that is in limited supply intraspecific competition -competition occurs within a given population; two types, either interference competition aka contest competition or exploitation competition aka scramble competition interspecific competition -among populations of different species (will be discussed in chapter 52) interference competition -aka contest competition; certain dominant individuals obtain an adequate supply of the limited resource at the expense of other individuals in the population; populations experience relatively small drop in population size, ex: birds nesting exploitation competition -aka scramble competition; all the individuals in a population "share" the limited resource more or less equally so that at high population densities none of them obtains an adequate amount; populations in this usually oscillate over time and can possibly drop to zero. ex: deer population The effects of density-dependent factors are difficult to assess in nature Density-independent factors are generally abiotic density-independent factor -any environmental factor that affects the size of a population but is not influenced by changes in population density; ex: random weather events
*density dependent and independent factors can be interrelated; such as high density of sheep huddling together to get protection from storm that is a density-independent factor Review -What are three examples of density-dependent factors that affect population growth? What are three density-independent factors? LIFE HISTORY TRAITS 5. Contrast semelparous and iteroparous reproduction 6. distinguish among species exhibiting an r strategy, those with a K strategy, and those that do not easily fit either category 7. describe Type I, Type II, and Type II survivorship curves, and explain how life tables and survivorship curves indicate mortality and survival. semelparous -species that expend their energy in a single, immense reproductive effort are said to be this; often they die; common in insects, invertebrates, fish, plants, invertebrates iteroparous -exhibit repeated reproductive cycles; common in vertebrates; perennial herbaceous plants, shrubs, trees, life history traits - such as semelparity and iteroparity; includes adaptations such as reproductive rate, age at maturity, and fecundity; There are two extremes: rselected species and K-selected species (are oversimplifications) fecundity -potential capacity to produce offspring fitness -ability of an individual to reproduce successfully, thereby making a genetic contribution to future generations of a population r selection - concept: populations that have traits that contribute to a high population growth rate; r stands for per capita growth rate; species with high r slection are called r strategists or r-selected species *typically are/have small body size, early maturity, short life span, large broods, little or no parental care, found in unpredictable environment where long term survival is low K selection - traits maximize the chance of surviving in an environment where the number of individuals (N) is near the carrying capacity (K) of the environment; organisms are called K strategists or K-selected species *do not produce large numbers of offspring, have long lifespans with slow development, late reproduction, large body size, and a low reproductive rate; found in stable environments;
have high competitive ability; have parental care; reach near K capacity; starvation is uncommon Life tables and survivorship curves indicate mortality and survival life table -shows the mortality and survival data of a population or cohort at different times during their life span. cohort -a group of individuals of the same age *PAGE 1013 understand what columns mean and how to get other columns from other columns. survivorship -probability that a given individual in a population or cohort will survive to a particular age. survivorship curve - produced by plotting logarithm (base 10) of the number of surviving individuals against age, from birth to the maximum age reached by any individual; are three main types Type I - ex: humans and bisons; high infant survival; morality concentrated later in life Type II -death spread evenly among age groups; rare; usually/essentially caused by random events; some lizards display this Type III - death greatest among young; ex: is oysters who are vulnerable in larval stage *herring gulls at first have type III, then later in life have type II, THUS it can be mixed. Review -What are the advantages of semelparity? Of iteroparity? Are there disadvantages? -Why is parental care of young a common characteristic of K strategists? -Do All survivorship curves neatly fit the Type I,II,III, models? Explain.