Population Ecology Chapter 9, Miller 14th Edition AP Environmental Science A.C. Mosley Mrs. Dow

Case Study: Sea Otters Are They Back From the Brink of Extinction Sea otters a tool-using mammals, uses stones to prey shellfish off rocks underwater and to break open the shells while swimming on the their backs and using their bellies as a table. They consume a ¼th of their weight each day in sea urchins, clams, mussels, crabs, abalones and about 40 other species of bottom-dwelling organisms. . They are the only marine mammal that lacks blubber, they can trap air under their fur for insulation. Early 1900’s almost extinct. They were hunted for fur and because they competed with fishers for valuable abalone. 1977 declared endangered. Most remaining species are found between California’s coastal cities of Santa Cruz and Los Angeles. (a) Southern sea otter (b) Sea Urchin (c) Kelp bed

Population Dynamics Outline Characteristics of a Population Population Dynamics and Carrying Capacity Reproductive Strategies Conservation Biology Human Impacts Working with Nature

9-1 Characteristics of a Population Population - individuals inhabiting the same area at the same time Population Dynamics: Population change due to Population Size - number of individuals Population Density - population size in a certain space at a given time Population Dispersion - spatial pattern in habitat Age distribution - proportion of individuals in each age group in population

Population Size Natality Mortality Number of individuals added through reproduction Crude Birth Rate - Births per 1000 Total Fertility Rate – Average number of children born alive per woman in her lifetime Mortality Number of individuals removed through death Crude Death Rate Deaths per 1000

Population Density Population Density (or ecological population density) is the amount of individuals in a population per unit habitat area Some species exist in high densities - Mice Some species exist in low densities - Mountain lions Density depends upon social/population structure mating relationships time of year

Population Dispersion Population dispersion is the spatial pattern of distribution There are three main classifications Clumped: individuals are lumped into groups ex. Flocking birds or herbivore herds due to resources that are clumped or social interactions most common http://www.johndarm.clara.net/galleryphots/

Population Dispersion http://www.calflora.net/bloomingplants/creosotebush2.html Uniform: Individuals are regularly spaced in the environment - ex. Creosote bush due to antagonism between individuals, or do to regular spacing of resources rare because resources are rarely evenly spaced www.agry.purdue.edu/turf/ tips/2002/clover611.htm Random: Individuals are randomly dispersed in the environment ex. Dandelions due to random distribution of resources in the environment, and neither positive nor negative interaction between individuals rare because these conditions are rarely met

Age Structure The age structure of a population is usually shown graphically The population is usually divided up into prereproductives, reproductives and postreproductives The age structure of a population dictates whether is will grow, shrink, or stay the same size

Age Structure Diagrams Positive Growth Zero Growth Negative Growth (ZPG) Pyramid Shape Vertical Edges Inverted Pyramid

Four variables influencing growth Births Deaths Immigration Emigration Increase  by birth & immigration Decrease  death & emigration Population change= (Birth+ Immigration)- (Death+Emigration)

Population Dynamics Outline Characteristics of a Population Population Dynamics and Carrying Capacity Reproductive Strategies Conservation Biology Human Impacts Working with Nature

Biotic Potential The biotic potential is the population’s capacity for growth The intrinsic rate of increase (r) is the rate of population growth with unlimited resources. Abiotic Contributing Factors: Favorable light Favorable Temperatures Favorable chemical environment - nutrients Biotic Contributing Factors: Reproductive rate Generalized niche Ability to migrate or disperse Adequate defense mechanisms Ability to cope with adverse conditions

Rapidly growing populations have four characteristics Reproduction early in life Short periods between generations Long reproductive lives Multiple offspring each time they reproduce A single house fly could total 5.6 trillion house flies within 13 months

Environmental Resistance Consists of all factors that act to limit the growth of a population Abiotic Contributing Factors: Unfavorable light Unfavorable Temperatures Unfavorable chemical environment - nutrients Biotic Contributing Factors: Low reproductive rate Specialized niche Inability to migrate or disperse Inadequate defense mechanisms Inability to cope with adverse conditions

Environmental Resistance Biotic Potential factors allow a population to increase under ideal conditions, potentially leading to exponential growth Environmental Resistance affect the young more than the elderly in a population, thereby affecting recruitment (survival to reproductive age)

Population Growth Population growth depends upon birth rates death rates immigration rates (into area) emigration rates (exit area) Pop = Pop0 + (b + i) - (d + e) ZPG (b + i) = (d + e)

Limits on population growth Carrying capacity [K] determined by biotic potential & environmental resistance This is the # of a species’ individuals that can be sustained indefinitely in a specific space As a population reaches its carrying capacity, its growth rate will decrease because resources become more scarce.

Population Growth Populations show two types of growth With few resource limitations Exponential J-shaped curve Growth is independent of population density The growth rate levels off as population reaches carrying capacity Logistic S-shaped curve Growth is not independent of population density

Exponential Growth As early as Darwin, scientists have realized that populations have the ability to grow exponentially All populations have this ability, although not all populations realized this type of growth Darwin pondered the question of exponential growth. He knew that all species had the potential to grow exponentially He used elephants as an example because elephants are one of the slowest breeders on the planet

Exponential Growth 19,000,000 elephants!!! One female will produce 6 young over her 100 year life span. In a population, this amounts to a growth rate of 2% Darwin wondered, how many elephants could result from one male and one female in 750 years? 19,000,000 elephants!!!

Exponential Growth Graph

Population Dynamics and Carrying Capacity Basic Concept: Over a long period of time, populations of species in an ecosystem are usually in a state of equilibrium (balance between births and deaths) There is a dynamic balance between biotic potential and environmental resistance

Carrying Capacity (K) Exponential curve is not realistic due to carrying capacity of area Carrying capacity is maximum number of individuals a habitat can support over a given period of time due to environmental resistance (sustainability)

No population can grow forever No population can grow forever. Exponential growth (lower part of the curve) occurs when resources are not limiting and a population can grow at near its intrinsic rate increase ( r ) or biotic potential. Such exponential growth is converted to logistic growth, in which the growth rate decreases as the population gets larger and faces environmental resistance. With time, the population size stabilizes at or near the carrying capacity ( K )of its environment and results in the sigmoid (s-shaped) population growth curve shown in this figure. Depending on resource availability, the size of a population often fluctuates around its carrying capacity.

Logistic Growth Because of Environmental Resistance, population growth decreases as density reaches carrying capacity Graph of individuals vs. time yields a sigmoid or S-curved growth curve Reproductive time lag causes population overshoot Population will not be steady curve due to resources (prey) and predators

Population overshoots carrying capacity 2,000 Population crashes 1,500 Number of reindeer 1,000 Carrying capacity When 26 reindeer (24 of them females) were introduced in 1910, lichens, mosses, and other food sources were plentiful. By 1935, the herd population had soared to 2,000 overshooting the islands carrying capacity. This lead to a population crash, with the herd plummeting to only 8 reindeer by 1950. 500 1910 1920 1930 1940 1950 Year Exponential growth, overshoot, and population crash of reindeer introduced to a small island off of SW Alaska

Population exceeds K Organisms die unless they move Changes in the physical environment can occur Reducing grass cover by overgrazing allows sagebrush to move in an reduces the number of cattle that the land can support Technology & cultural changes have extended K on Earth (temporarily)

Density of a population density Density-independent (affects population size regardless of its density) Floods, hurricanes, fire, pesticide spraying , pollution) Density-dependent (greater effect as population density increases) Competition for resources, predation, parasitism, disease – bubonic plague)

Population fluctuations in nature Stable (varies slightly above and below carrying capacity,K) Irruptive (explode to a high level and then drastically drop - insects) Cyclic (over a regular time period – lemmings populations rise and fall ever 3-4 years) Irregular behavior (no pattern)

General types of simplified population changes curves found in nature © 2004 Brooks/Cole – Thomson Learning (d) Irregular (a) Stable Number of individuals (c) Cyclic (b) Irruptive Time

Population size (thousands) 160 Hare 140 Lynx 120 100 Population size (thousands) 80 60 40 20 For decades, predation has been the explanation for the 10-year population cycle of the snowshoe hare and its predator, the Canadian Lynx. According to this top-down control hypothesis, lynx preying on hares periodically reduced the hare population. The shortage of hares then reduced the lynx population, which allows the hare population to build up again. At some point the lynx population increases to take advantage of the increased supply of hares, starting the cycle again. However, researchers have found that snowshoe hare have a 10 year boom-and-bust cycles on islands where lynx are absent. These scientist hypothesizes that the periodic crashes in the hare population can also be influenced by their food supply. Once the hare populations crash the plants can recover and the hare population begins rising again. If this bottom-up control theory is correct the lynx do not control the hare population. Instead, the changing hare population size may cause fluctuations in the lynx populations. It more than likely a combination of the two factors, predation and food supplies. 1845 1855 1865 1875 1885 1895 1905 1915 1925 1935 Year Predator – prey relationships Lynx-Hare Cycle Cyclic ever 10 years

Dynamic Equilibrium Dynamic equilibrium defines a population that is in balance with the carrying capacity of the environment. Most populations in nature show characteristics of dynamic equilibrium-a balance. This does not mean that they don’t go through exponential growth at some time or had diebacks.

Population Dynamics Outline Characteristics of a Population Population Dynamics and Carrying Capacity Reproductive Strategies Conservation Biology Human Impacts Working with Nature

Reproductive Patterns and Survival (9-2) Asexual reproduction Does not utilize sex Each cell divides & produce to identical cells (replicas of cell) Bacteria-Cell division Hydra - budding Shoal grass- rhizomes                                                                                

Sexual reproduction- 97% of earth species use it Gametes from each parent combine to produce offspring w/traits from each parent Issues: 1. Males cannot give birth -- females need to produce 2x the offspring to even population 2. Chance of genetic errors increase during recombination 3. Consume energy and time; transmit disease; can cause injury Why utilize? Great genetic diversity Can tolerate climate changes Males may help with food gathering

Reproductive Strategies Goal of every species is to produce as many offspring as possible Each individual has a limited amount of energy to put towards life and reproduction This leads to a trade-off of long life or high reproductive rate Natural Selection has lead to two strategies for species: r - strategists and K - strategists

r - Strategists Spend most of their time in exponential growth High rate of reproduction Little parental care Minimum life Opportunist K

R Strategists Many small offspring Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental conditions High population growth rate – (r) Population size fluctuates wildly above and below carrying capacity – (K) Generalist niche Low ability to compete Early successional species

K - Strategists Maintain population at carrying capacity (K) Maximize lifespan Competitor Follow a logistic growth curve K

K- Strategist Reproduce later in life Fewer, larger offspring High parental care and protection of offspring Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental conditions Lower population growth rate (r) Population size fairly stable and usually close to carrying capacity (K) Specialist niche High ability to compete Late successional species Prone to extinction

Survivorship Curves Late Loss: K-strategists that produce few young and care for them until they reach reproductive age thus reducing juvenile mortality Constant Loss: typically intermediate reproductive strategies with fairly constant mortality throughout all age classes Early Loss: r-strategists with many offspring, high infant mortality and high survivorship once a certain size and age Insurance companies use life tables of human populations to determine policy costs for customers. Life tables show that women in the U.S. survive an average of 6 years longer than men. This explains why a 65-year old American man normally pays more for life insurance than a 65-year old American women.

Effects of Genetic Variations on Population Size (9-3) Genetic diversity 1. Founder effect Few individuals move to a new location and are isolated from the original population Limited genetic diversity

2. Demographic bottleneck Few individuals survive a catastrophe- fire, hurricane Lack of genetic diversity may limit these individuals to rebuild the population 3. Genetic drift Random changes in gene frequencies May help or hurt survival of a population Some individuals may breed more than others and their genes may eventually dominate the gene pool of the population 4. Inbreeding Members of a small population exchange genes

Population Dynamics Outline Characteristics of a Population Population Dynamics and Carrying Capacity Reproductive Strategies Conservation Biology Human Impacts Working with Nature

Conservation Biology Careful and sensible use of natural resources by humans Originated in 1970s to deal with problems in maintaining earth's biodiversity Dedicated to protecting ecosystems and to finding practical ways to prevent premature extinctions of species

Conservation Biology Three Principles Biodiversity and ecological integrity are useful and necessary to all life on earth and should not be reduced by human actions Humans should not cause or hasten the premature extinction of populations and species or disrupt vital ecological processes Best way to preserve earth’s biodiversity and ecological integrity is to protect intact ecosystems that provide sufficient habitat

Habitat Fragmentation Process by which human activity breaks natural ecosystems into smaller and smaller pieces of land Greatest impact on populations of species that require large areas of continuous habitat Also called habitat islands

Habitat fragmentation in northern Alberta 1949 1964 Habitat fragmentation in northern Alberta 1982 1991

Population Dynamics Outline Characteristics of a Population Population Dynamics and Carrying Capacity Reproductive Strategies Conservation Biology Human Impacts Working with Nature

Human Impacts Humans have directly affected changes on about 83 % of Earth’s land surface. Humans have altered nature to meet our needs

Human Impacts Fragmentation and degrading habitat Simplifying natural ecosystems Destruction of the Earth’s NPP Strengthening some populations of pest species and disease-causing bacteria by overuse of pesticides Elimination of some predators

Human Impacts Deliberately or accidentally introducing new species Overharvesting potentially renewable resources Interfering with the normal chemical cycling and energy flows in ecosystem Increasingly dependent on nonrenewable energy from fossil fuels

Population Dynamics Outline Characteristics of a Population Population Dynamics and Carrying Capacity Reproductive Strategies Conservation Biology Human Impacts Working with Nature

Working with Nature Learn six features of living systems Interdependence Diversity Resilience Adaptability Unpredictability Limits

Basic Ecological Lessons Sunlight is primary source of energy Nutrients are replenished and wastes are disposed of by recycling materials Soil, water, air, plants and animals are renewed through natural processes Energy is always required to produce or maintain an energy flow or to recycle chemicals

Basic Ecological Lessons Biodiversity takes many forms because it has evolved over billions of years under different conditions Complex networks of + and – feedback loops exist Population size and growth rate are controlled by interactions with other species and with abiotic Organisms generally only use what they need

Four Principles for Sustainable We are part of, not apart from, the earth’s dynamic web of life. Our lives, lifestyles, and economies are totally dependent on the sun and the earth. We can never do merely one thing (first law of human ecology – Garret Hardin). Everything is connected to everything else; we are all in it together.

The Cats of Borneo Arrange the sentence strips in chronological order What happened first? Arrange the sentence strips in chronological order

Operation Cat Drop One of the most bizarre events to accompany this early use of DDT occurred when it became necessary to parachute cats into remote jungle villages in what was then Burma.  The following account was taken from a source at Cornell University: In the early 1950s, the Dayak people in Borneo suffered from malaria. The World Health Organization had a solution: they sprayed large amounts of DDT to kill the mosquitoes which carried the malaria. The mosquitoes died, the malaria declined; so far, so good. But there were side-effects. Among the first was that the roofs of people's houses began to fall down on their heads. It seemed that the DDT was also killing a parasitic wasp which had previously controlled thatch-eating caterpillars. Worse, the DDT-poisoned insects were eaten by geckoes, which were eaten by cats. The cats started to die, the rats flourished, and the people were threatened by outbreaks of sylvatic plague and typhus. To cope with these problems, which it had itself created, the World Health Organization was obliged to parachute14,000 live cats into Borneo.

The Day they Parachuted Cats into Borneo WHO sent DDT to Borneo. Mosquitoes were wiped out. Caterpillar numbers went up. Caterpillars ate grass roofs. Roaches stored DDT in their bodies. Lizards ate roaches and got DDT. Lizards slowed down. Cats caught lizards containing DDT. Lizards disappeared. Cats died. Rats increased. Rats brought the plague. Cats were parachuted in. The Day they Parachuted Cats into Borneo

Homework: Are They Competitors or Opportunists Homework: Are They Competitors or Opportunists? “k-selected and r-selected species lab” Worksheet is online look at today's calendar,it is also under Unit Five files. Either email it to me or print it off. You will need a computer with real player to view the video clips.