Topic 13 - Population Ecology STUDENT PDF

BIOLOGY 1 ASB0204 Topic 13 Population Ecology Nur Atikah Saleh Hodin Muhammad Amiruddin Ibrahim Azman Jali Biology Unit Centre For Foundation Studies In Science of Universiti Putra Malaysia  This lecture n...

BIOLOGY 1 ASB0204 Topic 13 Population Ecology Nur Atikah Saleh Hodin Muhammad Amiruddin Ibrahim Azman Jali Biology Unit Centre For Foundation Studies In Science of Universiti Putra Malaysia  This lecture note is adapted based on the book by Solomon, Martin, Martin & Berg Ebook:https://account.cengage.com/login Chapter 53 Chapter Introduction 01 to Ecology: Population Ecology BIOLOGY Eleventh Edition Solomon, Martin, Martin & Berg Outline 13.1/ (53.1) Population Ecology & Features of Population 13.2/ (53.2) Changes in population size 13.3/ (53.3) Factors influencing population size 13.4/ (53.6) Human populations  Learning outcomes By the end of this video lecture, you will be able to: 1. Define population ecology. 2. Explain four factors that cause changes in population size. 3. Explain the intrinsic rate of increase and carrying capacity, as well as differences between J and S-shaped growth curves. 4. Contrast density-dependent and density-independent factors. 5. Describe Type I, II and III survivorship curves and explain how the curves indicate survival and mortality. 6. Summarize human population growth. 13.1 Population Ecology Ecology is the study of how living organisms and the physical environment interact in a complicated web of relationships A population is all the organisms belonging to the same species occupying a certain area at the same time Population Ecology: ⮚ The study of population in relation to their environment, including environmental influences on population density and distribution, age structure and variations in population size 13.1 Features of population Features that characterize populations include population density, population dispersion, birth and death rates, growth rates, survivorship, and age structure. Population ecology considers the number of individuals of a particular species in an area and the dynamics of the population. ⮚ Population Dynamics is the study of changes in populations, how and why their numbers increase or decrease over time. 13.1 Features of population Further reading: Page 1152-1153 Researchers study a large population by sampling part of it and expressing the population in terms of density. Population density: the number of individuals of a species per unit of area or volume at a given time. Different environments vary in the population density of any species they can support. May be determined in large part by biotic or abiotic factors in the environment Population Dispersion ⮚ Individuals in a population may exhibit characteristic patterns of spacing relative to one another. 1. Random Dispersion ⮚ When individuals are spaced in a manner that is unrelated to the presence of others (rare). 3. Uniform Dispersion 2. Clumped Dispersion ⮚ Individuals are more evenly spaced ⮚ The species space their nests more or than a random pattern. less evenly.  13.2 Changes in population size Population growth is a change in the number of individuals in a population over time. Changes in a population is ultimately causes by two factors: ⮚ Natality ▪ the average per capita birth rate ⮚ Mortality ▪ the average per capita death rate Growth rate (r), or rate of change of a population on a per capita basis, is the birth rate minus the death rate. Besides natality and mortality, movement of individuals among population (dispersal) must be considered when examining changes in populations. Two types of dispersal: ⮚ Immigration ▪ when individuals enter a population and increase its size ⮚ Emmigration ▪ when individuals leave a population and decrease its size 13.2.1 Population growth Variation of population growth includes: ⮚ Positive population growth ▪ increase in population size (N) ⮚ Negative population growth ▪ decrease in population size (N) ⮚ Zero population growth ▪ no net increase or decrease in population size (N) 13.2.1 Population growth Population of all species have the potential to expand greatly when resources are abundant. Unlimited population growth does not occur for long in nature ⮚ Individuals typically have access to fewer resources as population grows. Population growth: The difference between the rates of birth and death in a given time ⮚ Occurs when birth rate > death rate ⮚ Occurs when immigration > emigration ⮚ Occurs due to the combination of these factors present 13.2.1 Natality, Mortality & Migration 13.2.1 Natality, Mortality & Migration If natality + immigration > mortality + emigration, population size increases If mortality + emigration > natality + immigration, population size decreases If natality + immigration = mortality + emigration, population size is stable Population Growth Rate, r: Birth Rate (natality rate) – Death Rate (mortality rate) 13.2.2 Intrinsic rate of increase The maximum rate at which a population of a given species could increase under ideal conditions, when resources are abundant and population density is low (rmax). Population growth is also depending on: 1. Biotic potential (r) 2. Environmental resistance 3. Carrying capacity (K) 13.2.2 Biotic Potential (r) and Survivorship Maximum number of offspring of an organism that would survive to reproductive age under ideal conditions ⮚ abundant resources ⮚ no limitation/environmental resistance ⮚ its population density is low Individual in the population can survive and reproduce at its maximum rate/ biotic potential (r- max) 13.2.2 Biotic Potential (r) and Survivorship Each species will have a different biotic potential depend on several factors: 1) The age beginning of reproduction 2) The species reproductive span - how long individual can reproduce Age Structure 3) Frequency of reproduction - how often reproduction occurs 4) How many offspring are born at a time 5) Survival rate of offspring - how many offspring survive to reproductive age 13.2.2 Biotic Potential (r) and Survivorship Survivorship = probability that a given individual in a population will survive in a particular age ⮚ Percentage of an original population that survives to a given age Number of survivors % survival = X 100% Number in original group By understanding survivorship, ecologists are able to study population growth. 13.2.2 Biotic Potential (r) and Further reading: Page 1161-1162 Survivorship Survival curves = percentage against age Three main survivorship curves: ⮚ Type I: ▪ Population whose survivorship highest in the early life cycle. ▪ Survival decreases as the age increases especially in post- reproductive years. ▪ Senescene is the major factor affecting mortality ▪ Eg: Human (in developed countries), primates 13.2.2 Biotic Potential (r) and Survivorship Survival curves = percentage against age Three main survivorship curves: ⮚ Type II: ▪ Population which mortality constant throughout life. ▪ Chances of death not increase or decrease. ▪ This type of survivorship is rare (Eg: Hydra and certain lizard species). 13.2.2 Biotic Potential (r) and Survivorship Survival curves = percentage against age Three main survivorship curves: ⮚ Type III: ▪ Mortality greatest in early life. ▪ Individual that survived to maturity have a very low mortality rate. ▪ Eg: Marine invertebrates, fish, mountain sheep, humans (in nations where starvation and disease are widespread) Biotic Potential (r) and Survivorship 13.2.3 Environmental resistance Environmental factors that limit the size of a population ⮚ Lower the chance for reproduction ⮚ Affect the health of the organism ⮚ Raise the death rate in the population 1. Biotic factors – living factors that affects a particular organism (population size) ⮚ Predation, competition, disease, parasitism 2. Abiotic factors – non-living factors, physical environment that affect a particular organism (population size) ⮚ Food, water, light, shelter, space, oxygen 13.2.4 Carrying capacity Carrying capacity (K) is the largest population that can be maintained for an indefinite period by a particular environment, assuming no changes in the environment. Results from the interaction between biotic potential (r) and environment resistance for a particular organism with a given set of environment resources ✔ Environmental resistant will limit the population growth and bring about death rates that equal the birth rates ✔ When this happen, the population size reaches a stable balance (K is reached) K is achieved when population growth rate slows down & maintain at a nearly steady state K can change with changing environment 13.2.4 Carrying Capacity Importance : To limit population size ⮚ prevent depletion of natural capital Ecosystem management ⮚ often serve as a basis for sustainable development 13.2.4 Carrying Capacity When population size exceeds K Environmental resistance increases Living organisms must adapt to new levels of consumption or find alternative resources Population size decreases (mortality rate > natality rate) When population size stable at K Natality rate = mortality rate (population growth rate = 0) Population has reached dynamic equilibrium When population size below K Resources will not be depleted (zero environmental resistance) Population has tendency to grow Population size increases (mortality rate < natality rate) 13.2.5 Population Growth Model There are two working models for population growth ⮚ Exponential growth ⮚ Logistic growth Some organisms do not exactly fit these two patterns Even so, ecologists have found it useful to develop mathematical models of population growth based on these two very different patterns of reproduction 1) Exponential Growth Model (Unlimited Growth Curve) Characterized by J-shaped curve ⮚ e.g. bacteria population growth The larger the population gets, the faster it grows. Populations will increase exponentially as long as their per Figure 53.2: Exponential population growth. When bacteria divide every 20 minutes, their numbers (expressed capita growth rates remain in millions) increase exponentially. The curve of exponential population growth has a characteristic J shape. The ideal constant. conditions under which bacteria or other organisms reproduce exponentially rarely occur in nature, and when these conditions do Population grows at max. rate (rmax) occur, they are of short duration and growth rate is defined as: dN = rmaxN dt Where; rmax = maximum rate of increase N = no. of ind. present at one time 1) Exponential Growth Model (Unlimited Growth Curve) Growth is unlimited and increase exponentially Environmental resistances is not limiting The growth curve of human population show how the increase of individual added each generation Reproduce at maximum biotic potential (r) Cause a large population growth 1) Exponential Growth Model (Unlimited Growth Curve) When a population is exhibiting exponential growth, the population is growing at or near their biotic potential (maximum growth rate) Can be divided into TWO phases i. Lag Slow growth at start (due to phase small number of reproducing individual in the original population) ii.Log Then increases rapidly over phase short period of time as the (exponential number of reproducing phase) individuals increases (hence the J-curve) May be due to: ⮚ Improve healthcare and medical ⮚ Increment of food production / agriculture 1) Exponential Growth Model (Unlimited Growth Curve) Boom and bust growth cycle In practice, the pattern of unlimited growth will prevail only for short periods Exponent growth will stop abruptly as environmental resistance become suddenly effective Results in growth pattern termed boom & bust which associated with some insect species & algal bloom 2) Logistic Growth Model (Limited Growth Curve) Characterized by S-shaped/ sigmoid curve shaped Logistic model describes a population increasing from a small number of individuals to a larger number that are ultimately limited by the environment Density dependent – the growth rate depends on population density. Population grows at max. rate (rmax) and growth rate is defined as: dN = rmaxN (K-N) Figure 53.3: Carrying capacity and logistic population growth. In many laboratory studies, exponential population dt K growth slows as the carrying capacity (K) of the environment is approached. The logistic model of Where; population growth, when graphed, has a characteristic S- shaped curve. rmax = maximum rate of increase N = no. of ind. present at one time K = carrying capacity 2) Logistic Growth Model (Limited Growth Curve) This curve is called “logistic” because the exponential portion of the curve produces a straight line when the log of N is plotted Environmental resistance is limiting Growth is limited and then stabilizes subject to the carrying capacity (K) of the particular environment 2) Logistic Growth Model (Limited Growth Curve) Can be divided into FOUR phases i. Growth rate is Lag phase slow Organisms are adapting to the new environment Low number of mature & reproductively active organisms A period of preparation for growth 2) Logistic Growth Model (Limited Growth Curve) Can be divided into FOUR phases ii. Growth rate is Log phase rapid/exponential (exponential Natality rate more phase) than mortality rate Abundant/ continuous supply of resources No environmental resistance (unlimited resources) Near the biotic potential 2) Logistic Growth Model (Limited Growth Curve) Can be divided into FOUR phases iii. Growth rate slows down Decelerating Environmental resistance (transitional exist restricts the phase) population growth Population approaching carrying capacity (K) Mortality rate increases; Natality rate decreases Food shortage, competition, limited space, accumulation of waste products 2) Logistic Growth Model (Limited Growth Curve) Can be divided into FOUR phases iv. Growth rate is Stationary zero phase Carrying capacity (K) is achieved Natality rate = mortality rate Population size remains constant / stabilized / in equilibrium 13.3 Factors Affecting Population Size Biotic and abiotic conditions play an important role in regulating population size in natural environments. A limiting factor refers to any of the factors (variables) in an environment capable of limiting a process, such as the growth, abundance, or distribution of a population of organisms in an ecosystem. Factors that affect population size fall into two categories: ⮚ Density-dependent ⮚ Density-independent 1) Density Dependent Factors If a change in population density alters how an environmental factor affects that population, then the environmental factor is density- dependent. The effects of density-dependent factors on population growth increase as the population density increases. Tend to slow down population growth by causing an increase in mortality or decrease in natality. Density dependent factors as negative feedback system: ⮚ As population density increases, density-dependent factors tend to slow population growth by causing an increase in death rate and/or a decrease in birth rate. ⮚ Population density declines. 1) Density Dependent Factors ⮚ Predation, disease, and competition are examples of density- dependent factors. ⮚ As the density of a population increases: o Predators are more likely to find prey. o The chance of transmitting parasites and infectious disease organisms increases. o Competition for resources such as living space, food, cover, water, minerals, and sunlight increases. Density Dependent Factors i) Competition Competition for the same limited resources Increased when the population density is high ⮚ Interspecific competition ▪ Individuals of different species compete for the same resources in an ecosystem. ⮚ Intraspecific competition ▪ An interaction in population ecology, whereby members of the same species compete for limited resources. Interference Competition Exploitation Competition (Contest Competition) (Scramble Competition) Only dominant members of a population All the individuals in the population share obtain sufficient resources the available resources such that none The weaker individuals that unable to obtains an adequate amount compete may die Drastic fluctuations of population size Decline in population size. Density Dependent Factors ii) Overcrowding Occurs at high population densities May cause excessive stress → abnormal behaviour Some populations show a decline in health, survivorship and reduced fecundity (the ability to produce an abundance of offspring) even when food is abundant Hormonal changes may occur which affect reproductive behaviour (infertility, spontaneous abortions, parental neglect) Aggressive behaviour also increases The effects - limit further population growth Density Dependent Factors iii) Territorial behaviour A type of interference competition Seen especially in birds and also in fish, reptiles, mammals and insects Behaviour of a male or together with its female partner guarding a territory fiercely so that other males or females are not allowed to enter Size of territory depends on the species of animals and their aggressiveness Little or no overlap between neighbouring territories of the same species Limits population size and distribution of animals ⮚ Ensure enough preys ⮚ Cause population size and distribution to remain unchanged for a long time The birds without territories often die from predation or starvation Density Dependent Factors iv) Predation Interspecific interaction which results in cyclic fluctuations in population size An increase in the prey population supports an increased predator population Leads to a drastic drop in the number of prey organisms followed by an decline in the predator population v) Parasitism and disease In high-density populations, parasitic infections and disease spread more easily More individuals succumb to these factors → an increase in mortality. Inhibits further population growth in a manner similar to the prey-predator interaction. Density Dependent Factors v) Accumulation of toxic waste As a population grows, waste products from metabolic reactions accumulate and this may poison the members of the population It slows down the population growth thus population size decrease 2) Density Independent Factors Any environmental factor that affects the size of a population but is not influenced by changes in population density. Usually abiotic and are typically weather or climatic factors. Example: Mosquito populations in arctic environments; no adult mosquito survives winter; the entire population grows in summer from eggs and hibernating larvae i) Temperature ii) Light intensity iii) Wind Influence the activity of Influences the rate of Wind influences the enzyme in organisms photosynthesis in support of plants, the Distribution of plants evaporation rate and organisms are higher Areas that have the also cause erosion in areas that have optimal light intensity – Number of organisms optimal temperature for more plants available, are generally lower in the action of enzyme which indirectly areas that have strong increase the number of winds consumers in the area 2) Density Independent Factors Factors which are not influenced by changes in population density Usually abiotic and are typically weather or climatic factors iv) Oxygen v) Water Oxygen is needed for Water current influences the aerobic respiration in distribution of nutrients in the water organisms and high current may even move Areas with a higher oxygen the organisms to other areas content generally have a Water is also needs for cellular higher distribution of metabolism such as respiration organisms The areas with a good water supply will have more organisms compared with areas that have less water. 13.4 Human Populations The world population increases by about 100 million people per year and reached 8 billion people in 2022 (according to United Nation) Recent increase in human population is due to a decrease in death rate, not an increase in birth rate. Greater food production, better medical care, and improved sanitation practices have increased life expectancies 13.4 Human Population Growth Example: Mexico Both birth and death rates declined during the 20th century, but because the death rate declined much more than the birth rate, Mexico has experienced a high growth rate. 13.4 Human Population Growth Zero Population Growth Although human numbers continue to increase, the world per capita growth rate (r) has declined from a peak of 2.2% per year (mid-1960s) to 1.2% per year (2013) ⮚ Growth rate may continue to decrease until the birth rate equals the death rate (r = 0) and the S curve replaces the J curve Earth’s Carrying Capacity Earth’s carrying capacity is the main unknown factor in projecting population growth, which may range from 4 billion to 16 billion humans ⮚ Estimates vary widely because of assumptions made about standard of living, resource consumption, technological innovations, and waste generation ⮚ Earth can support far fewer humans if everyone lives lifestyles is similar to the people in highly developed countries Human Demographics and Age Structure Human Demographics Human population statistics such as size, density, and distribution must be considered to determine the population in various countries. ⮚ Countries can be classified into two groups based on their rates of population growth, degrees of industrialization, and relative prosperity: highly developed and developing ⮚ Developing countries have two subcategories: moderately developed and less developed Human Demographics and Age Structure Highly developed countries Moderately developed countries ⮚ Highly industrialized ⮚ Birth rates and infant mortality ⮚ Low rates of population growth rates generally high, but declining ⮚ Low birth rates ⮚ Medium level of industrialization ⮚ Low infant mortality rates ⮚ Lower average GNI PPP per ⮚ Long life expectancies capita ⮚ High average gross national income at purchasing power parity (GNI PPP) per capita Less developed countries ⮚ Highest birth rates and infant mortality rates ⮚ Lowest life expectancies ⮚ Lowest average GNI PPP per capita Age Structure Age structure is the number and proportion of people at each age in a population ⮚ An age structure diagram represents the number of males and females at each age, from birth to death ⮚ The overall shape of an age structure diagram indicates whether the population is increasing, stationary, or shrinking Age Structure - Less developed countries For less developed countries, the age structure diagram is shaped like a pyramid ⮚ A strong population growth momentum exists because the largest percentage of the population is prereproductive (0-14 years of age) – probability of future population growth is great ⮚ Even if fertility rates in these countries decline to replacement level, the population will continue to grow for some time Age Structure - Highly developed countries For highly developed countries, age structure diagrams have more tapered bases – smaller proportion of population is prereproductive ⮚ Diagram of a stable population shows approximately the same number of people at prereproductive and reproductive ages ⮚ In a population that is shrinking, the prereproductive age group is smaller than either reproductive or postreproductive group Age Structure Diagrams These age structure diagrams for (a) less developed countries and (b) highly developed countries indicate that less developed regions have a greater percentage of young people than do highly developed countries. As a result, less developed countries are projected to have greater population growth than are highly developed countries. (Adapted from Population Reference Bureau using data from United Nations, World Population Prospects: The 2002 Revision, 2003.) Summary Type I Biotic Potential (r) Type II and Survivorship Type III Environmental resistance Natality, Population Mortality & Migration Growth Carrying capacity Population Growth Model Limiting Factors Affecting Population Size and Distribution Density Density Dependent Independent Factors Factors THANK YOU