Presentation on theme: "Introduction to Ecology: Population Ecology Part 1"— Presentation transcript:
1 Introduction to Ecology: Population Ecology Part 1 Biology 213 Chapter 53Introduction to Ecology:Population Ecology Part 1*The world human population in 2004 is now estimated to be about 6.4 billion people, doubling every 40 years.
2 You will be able to… List various fields of study in Ecology Explain what factors change populationsCalculate population rate changesCompare and contrast density-dependent to density-independent factors
3 Ecology: Oikos = home Ology = study of Integrates all biological fieldsOrganismal ecology: physiology, behavior, interactions with environmentPopulation ecology: factors affecting groups of individuals in an area.Community ecology: interactions between species in an area
4 Ecosystem ecology: biotic and abiotic interactions; E flow & chem Ecosystem ecology: biotic and abiotic interactions; E flow & chem. CyclesLandscape ecology: exchange of E & materials across multiple ecosystems6. Global ecology: biosphere: regional exchange of E & materials affecting entire functioning & distribution of organisms wotldwide.
5 Ecology & environmental issues Complexity of Nature: Ecology & evolution: changes in environment impacting populations’ alleles over time.Ecology & environmental issuesComplexity of Nature:Why are some species present in an area?Dispersal difficulties (accessibility?)Behaviour limits distribution (habitat preference)?Biotic factors: competition/parasitism/predation/etcAbiotic factors:Chem: H2O, O2, pH, salinity, nutrientsPhys: Macro & micro climate: Temp, light, fire, soil composition, moisture
6 Estimate: one million years to get from 2 Estimate: one million years to get from 2.5 million to human population of ~ 5 million people in 6000 B.C. (2x)population did not reach 500 million until almost 8,000 years later -about 1650 A.D (100x)doubled roughly once every thousand years or soreached a billion ~ 1850, doubling in 200 yearsreached two billion around 1930 – doubling in 80 years1970’s it reached 4 billion ~ 40 year doubling timeToday’s population ~ 7 billion
7 What factors have allowed human population to increase so rapidly?
8 Ecologists study population trends rather than individual organisms. Properties of populations includePopulation sizePopulation densityPatterns of dispersionDemographicsPopulation growthLimits on population growth
9 Population dispersion (spacing) Population density# individuals of a species per unit at a given timePopulation dispersion (spacing)How are individuals distributed in a habitat?Why would this be important to know if you were studying a population?What does a dispersion pattern tell you?
10 Individual members distributed in a # of different ways: Clumped -Uniform -Random -
11 Why would a clumped population pattern form? individuals _____________ to each other,or __________________________________.
12 What factors encourage a uniform population pattern? individual organisms actively _____ each other or all _________________________________
13 What abiotic or biotic features would encourage a random population pattern? Rare in nature - occurs in absence of strong attractions or repulsions among individuals.
14 Dispersion patterns and density may change over time Habitat changes: food, nutrients, water, sunlight (plants)Age / size / developmental stages change:
15 Four factors that produce changes in population size 1. Two events increase populations:BirthImmigrationEvery time an animal is born, it's added to the population. The total number of animals born to a population each year can be counted or estimated.Rodents such as mice may have about five babies in a litter and have several litters per year. On the other hand, elephants have just one young every two years. Painted turtles lay from two to twenty eggs a year, but they don't all survive to become adults.Another event that increases population is immigration, or when animals move into a new area. Animals leave their homes to find new ones if their old habitat is too crowded, if they can't find a mate, or if their old habitat is destroyed. Leaving an old habitat is called emigration. 2. Two events decrease populations:DeathEmigrationWhen an animal dies it is subtracted from the population. Animals die from old age, starvation, disease, predation, or accidents. Sometimes the beginning of life is the most dangerous because young animals are easier for predators to catch.
27 Factors encouraging immigration: New environment made availableNatural disasters large and smallCompetitive or predatory species goes extinct / moves awayClimate change or new resourcesHitch-hiking (“alien” species)Less competition in new area
28 Succession after a disaster Immigrants have an opportunity to invade:Reduced competition
29 Factors that encourage successful immigration: Distribution methods:dispersal is at or near ground level vs.aerial dispersaldispersers actively engage in searching,or notdispersers able to orient toward preferredhabitat from some distance,
30 Wind dispersing Golden Orb spiders Small animals, such as mites and spiderlings, may disperse by launching themselves into a convective updraft and entering the “aerial plankton” (Richter 1970). The behavior and orientation abilities of aerial plankters descending from the atmosphere is not well understood, although there is evidence that they may be “scrubbed” from the atmosphere by rain (Russell 1999). Aerial plankters with little control over their ultimate destination, such as seeds or fungal spores, would be deposited onto habitat patches in direct proportion to patch area. Those failing to land in a patch might die if the matrix is a hostile environment. For such organisms, we would expect no relationship between patch size and the number of immigrants per unit area. Thus, all else being equal, we would expect no relationship between patch size and populaton density—the “random-sample hypothesis” (e.g., Andrén 1994).Large insects, such as the spruce budworm, may also disperse in the aerial plankton, and may similarly be deposited by weather events such as thunderstorm downdrafts (Greenbank et al. 1980). However, unlike mites and spiderlings, larger insects landing outside a patch are unlikely to die immediately; instead, they would continue searching, some randomly (Fig. 2B). For example, after its daily egg-laying bout, a female cabbage butterfly (Pieris rapae) disperses at an altitude of about 100 m, for a distance of about 450 m, in a random direction. The following day she randomly searches at ground level for host plants. Because of the ground-level search, this dispersal behavior results in a negative relationship between host patch size and density of cabbage butterfly eggs and larvae (Fahrig and Paloheimo 1987); see Fig. 2B. Long-jawed orb-weaving spiders (Tetragnatha elongata) discover woodland patches through random unoriented movement (Gillespie 1987), as in Fig. 2B; all else being equal, we would predict a negative relationship between patch size and population density for this species.Other insects that disperse in the aerial plankton make the final approach to patches low to the ground, orienting toward patches using some interplay of visual and olfactory cues (Prokopy and Owens 1983). Those for which vision dominates, such as the apple maggot fly Rhagoletis pomonella, which is attracted to silhouettes of host trees (Moericke et al. 1975), would find patches in proportion to their linear dimensions, resulting in lower densities in larger patches. Insects that locate their resources primarily by olfaction, such as the cabbage fly (Erioischia brassicae; Hawkes 1974), might be expected to find patches in direct proportion to their area. Density of such species would show no relationship to patch size.
31 Emigration Unfavorable Factors: *Excessive competition: mates or food *Lack of resources*Disease*Avoidance of in-breeding
32 Population change includes immigration and emigration: r = (birth rate) – (death rate) plus(immigration – emigration)e.g. Example: N = 300,000 humans:3000 births deaths in one year3,000 immigrated into the area9,000 emigrated out of the area
33 r = (b – d) + (i – e) b – d = (10/1000) – (5/1000) = 0.005 = – =r = (b – d) + (i – e)= (0.005) + (-0.002) = x 100 = 0.3%Growth rate: rN = (0.3%)(300,000)= 900 more people in the population
34 Intrinsic rate of increase (rmax) Maximum rate at which species orpopulation can increase under idealconditionsExponential population growth
36 According to Malthus:Population, when unchecked, increases in a geometrical ratio.Subsistence increases arithmetically.In 1798 the Englishman Thomas R. Malthus posited a mathematical model of population growth. He model, though simple, has become a basis for most future modeling of biological populations.Malthus's observation was that, unchecked by environmental or social constraints, it appeared that human populations doubled every twenty-five years, regardless of the initial population size. Said another way, he posited that populations increased by a fixed proportion over a given period of time and that, absent constraints, this proportion was not affected by the size of the population.By way of example, according to Malthus, if a population of 100 individuals increased to a population 135 individuals over the course of, say, five years, then a population of 1000 individuals would increase to 1350 individuals over the same period of time.According to Malthus, “ the power of population is indefinitely greater than the power in the earth to produce subsistence for man. Population, when unchecked, increases in a geometrical ratio. Subsistence increases only in an arithmetical ratio.”Darwin used this idea to help formulate his theories, particularly natural selection
37 Carrying capacityCarrying capacity (K) = largest population maintained without degrading environment they live inChanges as environment changesLogistic population curve(S-shaped curve)
38 Carrying capacity and logistic population growth Limiting FactorsK-N/K represents the limiting factors affecting the population growth rate. A small N
39 Density-dependent factors Regulate population growth by affecting large proportion of population as population rises:
40 Density-dependent factors What do you think would impact a population as it got bigger?PredationDiseaseCompetitionToxic wastes
41 Density-dependent factors and negative feedback
42 Density-independent factors Limit population growth but are not influenced by changes in population density: usually ABIOTICExamples include natural disasters:HurricanesBlizzardsForest firesMudslidesVolcanoes, tsunamis, and earthquakes
43 Limiting Factors Biotic and abiotic, Density dependent or independent factors that limit a population’s growth:What would be a limiting factor?
44 What can you think of that would be a limiting factor?Which are biotic and which are abiotic?increase death ratedecrease birth ratelimits immigrationencourages emigrationAny factors that slows population growth.
45 How are up & down cycles explained? Can be very complex relationships and factors.
46 Introduction to Ecology: Population Ecology Part 2 Biology 213 Chapter 53Introduction to Ecology:Population Ecology Part 2*The world human population in 2004 is now estimated to be about 6.4 billion people, doubling every 40 years.
47 You will be able to… Explain what factors change populations Calculate population rate changesCompare and contrast density-dependent to density-independent factorsAnalyze human population patterns and make predictions about future trends
48 Semelparous reproduction Expend their energy in aIteroparous reproductionExhibit ________________________throughout their lifetimes
49 Semelparity: Expend energy to reproduce in one big effort Most insects, invertebrates, many annual plants, and some fishWhat’s the advantage?
50 Iteroparous reproduction Expend energy to reproduce in cyclesMost vertebrates, perennial plants.What’s the advantage?
51 Species exhibiting an r strategy Emphasizes a high growth rateOrganisms typically havesmall body sizehigh reproductive ratesshort life spansinhabit variable environmentsOften
52 Species exhibiting a K strategy Maintains a population near carrying capacity (K) of environmentSpecies often havelarge body sizelow reproductive rateslong life spansinhabit stable environmentsOften
53 Survivorship curvesType IMortality is greatest in old ageType IIMortality is spread evenly across all agesType IIIMortality is greatest among the young
56 Survivorship curve for a herring gull population
57 Source habitats: Preferred habitats Local reproductive success is > local mortalityLocal individuals disperse from source habitats to other regions
58 Sink habitats Lower-quality habitats Individuals may suffer death or poor reproductive successWhat would make an organism move then?
59 Source & sink populations in a hypothetical metapopulation
60 Human population growth World population reaches 6,668,926,425 by May 20, 2008Per capita growth rate declined from peak in 1965 of about 2% per year (doubling time 35 years)to 1.3% per year (doubling time of 54 years)birthrate necessary for zero population growth is 2.1 births per woman7,000,000,000The year 2011
61 Human population growth: exponential J-shaped curve so far
63 Chapter 53 Clicker Question #4: Often growth cycles of one population affects the cycle of another. As moose populations increase, wolf populations also increase. If we consider the logistic equation for the wolf population:dN = rN (K-N)dt Kwhich of the above factors accounts for the strongest impact on the moose population?A. K B. dN C. rN D. dt
64 Highly developed countries Population characteristicsHighly developed countrieslow birth ratelow infant mortalitylow fertility ratelong life expectancieshigh GNI PPP:GNI PPP per capita is the gross national income in purchasing power parity divided by mid-year population.TOTAL EARTH'S SURFACE = 197 million square miles = 510 million square kilometers TOTAL WATER SURFACE = 140 million square miles = 363 million square kilometers TOTAL LAND SURFACE = 57 million square miles =147 million square kilometers (From Colliers Encyclopedia) OF THE TOTAL AREA OF LAND SURF ACE OF EARTH: 57 million milcs2 x 640acrcs/square mile = 36,480,000,000 acres 2.5 acres to support one family (2 adults, 2 children) or acres per personFrom the January 1992 FAO Report (Food and Agriculture Organization of the United Nations)11 % of land surface suitable for agriculture (22%) with appropriate irrigation and drainage6% permafrost10% too wet22% too shallow23% with chemical problem28% too dry. TWO ASSUMPTIONSOnly 11% of the land surface is suitable for agriculture.It takes acres of suitable land to support each person. TOTAL LAND SURFACE = 57 million square milesTotal land suitable for agriculture = 57,000,000 miles2 x 0.11 = 6,270,000 square milcs = 6.27 million x 640 acres/mile2 = 4,012.8 million acres or 4 billion acres.At acres per person: million acres/person = million or about 6.4 billion people. Therefore, based on the above assumptions, the world can support about 6. 4 billion people In order to prevent heavy and unnecessary loss of human life at that population level:There will be no erosion or deterioration of the present available arable land.Everyone on earth will be vegetarian (no cattle).There will be no military and no war.Thcrc will be no population increase beyond 6.4 billion.There will be no pets (dogs or cats).There will be no insect pests.There will be no plant diseases.There will be no trains, boats, automobiles, RVs, ORVs, airplanes or other vehicles or machinery to necessitat~ exploiting resources or increasing global warming.There will be no use of agriculture lands to build cities.There will be no wealthy people, everyone will live at the very lowest level of subsistence.There will be no unusual or disastrous climatic changes.There will be no plagues or new diseases (heavy population density would facilitate extremely rapid spread of any disease).
65 Population characteristics Developing countrieshigh birth ratehigh infant mortalityhigh fertility rateshort life expectancieslow GNI PPP
66 China and India’s populations increasing What trends do we see world-wide?China and India’s populations increasing
67 Birth rate decline lags behind as death rate decreases: e. g Birth rate decline lags behind as death rate decreases: e.g. in Mexico, 1900–2000
68 Age structure influences population dynamics Possible for country to have replacement-level fertility and still experience population growthYoung age structure causes a positive population growth momentum as large pre-reproductive age group matures
69 15-to-40 range: reproductive rates are high Age structure diagrams comparing Kenya to USA to Germany15-to-40 range: reproductive rates are high
70 “Carrying-capacity" definition of overpopulation: not population density, but #’s of people in an area relative to resources capacity to sustain human activitiesa condition of overpopulation might be corrected with no change in the number of people!
71 Ecological FootprintDeveloping countries tend to have people overpopulation that degrades the environmentDeveloped countries have consumption overpopulation that degrades the environment
76 Above: Bhutan Below: Chad One week’s food costs the Chad family $1.23
77 China has 22 % of world’s population India has 17 % of world’s populationBoth nations are modernizing rapidlyUSA uses has 4.4% of the world population and uses 25% of world’s energy resourcesWhat happens to global resources when developing countries want to enjoy a developed nation lifestyle like ours?China's present population of 1.4 billion, despite the governmental policy of permitting only one child per couple, is still growing at an annual rate of 0.6 percent. Although China recognizes its serious overpopulation problem and recently passed legislation strengthening the policy, its young age structure means that the number of Chinese will continue to increase for another 50 years. India, with nearly 1.1 billion people (living on approximately one-third the land of either the United States or China), has a current population growth rate of 1.7 percent per year. This translates to a doubling time of 41 years. Taken together, the populations of China and India constitute more than one-third of the total world population.