Wildlife Health & Disease (VMS4007/123) PDF

VMS4007/123: WILDLIFE HEALTH & DISEASE Introduction to population ecology- Part 2 Dr Tara Pirie- [email protected] Please e-mail if you have any questions 1 Population ecology: learning objectives Describing population growth - Understanding the component parts of an exponential growth model...

VMS4007/123: WILDLIFE HEALTH & DISEASE Introduction to population ecology- Part 2 Dr Tara Pirie- [email protected] Please e-mail if you have any questions 1 Population ecology: learning objectives Describing population growth - Understanding the component parts of an exponential growth model and how they interact. - Describe logistic growth and the factors that limit this. - Understand how density dependent and density independent factors provide feedback into a model. - Understand what r- and K-strategists are Population dynamics modelling: A population’s growth rate Births Births and immigration add individuals to a population. Immigration Deaths Deaths and emigration remove individuals from a population. Emigration Population dynamics modelling: A population’s growth rate Deaths Births Deaths and emigration remove individuals from a population. Births and immigration add individuals to a population. Immigration Change in population size Emigration = Births + Immigrants entering population – Deaths – Emigrants leaving population A population’s growth rate (aka Per Capita Rate of Increase) Birth rate - death rate = A population’s growth rate The population growth rate can be expressed mathematically as: N is the change in population size t is the time interval B is the number of births D is the number of deaths A population’s growth rate (aka Per Capita Rate of Increase) Births and deaths can be expressed as the average number of births and deaths per individual during the specified time interval: • b is the annual per capita birth rate • m (for mortality) is the annual per capita death rate • N is population size The population growth equation can be revised: B = bN D = mN A population’s growth rate (aka Per Capita Rate of Increase) The per capita rate of increase (r) aka intrinsic growth rate is given by: r=b–m • Zero population growth - (r = 0) occurs • Population increases - (r > 0) occurs = > • Population decreases < - (r < 0) occurs Remember: Change in population size can now be written as: N t = rN Exponential Growth Exponential population growth: population increase under idealized conditions. The rate of increase is at its maximum, denoted as rmax Think of N as money in a bank account and r as interest on the account! Population dN The equation of exponential population growth is: = rN dt Time E.g. 5% interest £1,000 – interest added after 1 year - add £50 = £1,050, £1,050 - interest added after 2 years - add £52.50 = £1,102.50 Exponential Growth A J-shaped curve Population size (N) 2,000 dN = 1.0N dt 1,500 dN = 0.5N dt 1,000 The rate of increase is constant, but the population accumulates more new individuals per unit time when it is large than when it is small 500 0 0 5 10 Number of generations 15 Exponential Growth Constant growth rate = Constant per capita increase High Population increases - (r > 0) > Low How realistic is this? When do populations show exponential growth in nature? ? Nb - Only under idealised, Non limiting conditions J shaped curve with r = max at all population sizes Exponential Growth: Does it occur in nature? E.g. - If populations introduced to new area Rebound following catastrophe / hunting Kruger NP - (1898/1926) Greater Kruger NP (1 million ha) Result? - Habitat erosion What then? - Limits imposed: culling (1967-1995) birth control ( b, 1996 on) export (emigration, 2001 on) water sources - reduced Population Growth: Modelling logistic growth • BUT Exponential growth cannot be sustained for long in any population WHY? • Resources become limited as population increases: food, shelter, water, disease, predation…. • A more realistic population model limits growth by incorporating carrying capacity Carrying capacity (K) is the maximum population size the environment can support. K varies with the abundance of limiting resources Population Growth: Modelling logistic growth The logistic model describes how a population grows more slowly as it nears its carrying capacity (K) As maximum population size approaches K: b or m →r i.e. slows down (K – N) dN = rN dt K K = 1500 N = 1200 (gives 300 / 1500 = 0.2) N = 100 (gives 1400 / 1500 = 0.93) “K” Population Modelling it into the equation: Gives a sigmoidal (S-shaped) curve Time Population Growth: Modelling logistic growth Exponential growth dN Population size (N) 2,000 = 1.0N dt 1,500 K = 1,500 dN = 1.0N 1,000 1,500 − N dt Logistic growth 500 Population growth begins slowing here. 0 0 10 15 5 Number of generations 1,500 Population Growth: Logistic growth in nature A sigmoidal curve? occurs in simple organisms in the lab… BUT in other ‘natural’ populations it assumes: 1. Instantaneous adjustment real populations show lag & so overshoot, then undershoot, then… 2. Individuals have same impact at low density individual impact may be less or more positive: Allee effect (strong/weak) i.e. mate location Depending on the species (& its phenology) below a critical population size (caused by undershoot?), extinction may be likely Population Change and Population Density There are two general questions about regulation of population growth: • Why do some populations show radical fluctuations in size over time, while others remain stable? • What environmental factors stop a population from growing indefinitely? Algae in Lake Erie ? In density-dependent limitations: < Birth rates fall and death rates rise with population density (i.e. factors that affect population size in relation to the population’s density). In density-independent limitations: Birth rate and death rate do not change with population density (i.e. factors that limit population size regardless of the population’s density). Density dependent factors Competition • Interspecific = between species • Intraspecific = within species • • As population density , resources Amount per capita towards K decreases as difficult to grow / reproduce < Density dependent factors Disease • As population density • Population density can influence the health and survival of organisms • In dense populations, pathogens can spread more rapidly , disease < Density dependent factors Predation • As population density , predation • Peregrine falcon: nuthatch/blackbird dunlin / curlews • Cats, dogs - impacts on wildlife: Direct Indirect Peregrine falcon Nuthatch Blackbird < Density dependent factors Territoriality • As population density , territories • In many vertebrates and some invertebrates, competition for territory may limit density • (dispersion and % of non-breeders) < Density dependent factors Intrinsic factors • As population density , intrinsic factors • For some populations, intrinsic (physiological) factors appear to regulate population size. • E.g.: stress, aggression MacNulty et al. (2014) https://doi.org/10.1111/1365-2656.12238 < Density dependent factors Toxic wastes • As population density , toxic waste < • Accumulation of toxic wastes can contribute to density-dependent regulation of population size 5 µm Density independent factors: • Chance events or external factors • Weather (cold wet winters, drought) • Seeds finding fertile soil Pop. Growth:“Trade-offs” and Life Histories Principal of Allocation Time Energy Nutrients Organisms have finite resources, which may lead to trade-offs between survival and reproduction Reproduction/Breeding costs: “Fast” life history “Slow” life history Live fast and die young? Live long and prosper? Fewer, larger young Make more young / smaller Parents surviving the following winter (%) Pop. Growth:“Trade-offs” and Life Histories E.g. There is a trade-off between survival and paternal care in European kestrels 100 Male Female 80 60 40 20 0 Reduced brood size Normal brood size Enlarged brood size Pop. Growth: Reproductive strategies Reproductive choices: • • • • Semelparity v iteroparity – (S=single) Age of breeding Number & size of offspring Parental care Octopus - Semelparity Tree kangaroo - Iteroparity Pop. Growth: Reproductive strategies Trade of between quantity (number) and quality (survival) of offspring K-selection (density-dependent selection (DD)): • • Lives in more stable environment. Selects for offspring that have a higher probability of survival to maturity – greater quality r-selection (density-independent selection (DI)): • • Lives in unstable and unpredictable environments Selects for life history traits that maximize reproduction (per capita rate of increase) Pop. Growth: Reproductive strategies: K/r selection Trade of between quantity (number) and quality (survival) of offspring r-selected Unstable env. (DI) K-selected Stable env. (DD) Small Large Low High # Offspring produced Many Few Timing of maturation Early Late Life expectancy Short Long 1 >1 Type III Type I or II Characteristics Organism size Energy used to make individ Lifetime reproductive events Survivorship curve Population ecology: learning outcomes Survival and reproductive success impact population growth… … but population size impacts survival and reproductive strategy - Understanding the component parts of an exponential growth model and how they interact. - Describe logistic growth and the factors that limit this. - Understand how density dependent and density independent factors provide feedback into a model. - Understand what r- and K-strategists are - How you might impact the world as a vet! Example questions 30 What does “N” represent in the capture-mark-recapture equation? MxC=N R 31 What does “N” represent in the capture-mark-recapture equation? MxC=N R Population size (N) If you have not done so watch the recommended video about counting pingpong balls and London taxis! Link is on the equation page 32 Time specific (Static) life table is based on: a) 1 age group at a specific time b) 1 group which is followed from birth to death c) All age groups at a specific time d) All age groups followed for 5 years 33 Time specific (Static) life table is based on: a) 1 age group at a specific time b) 1 group which is followed from birth to death c) All age groups at a specific time d) All age groups followed for 5 years c) All age groups at a specific time – a snap shot of the population much like the census in the UK 34 Type 1 survivorship curve shows: i) Constant rate of decline ii) Low mortality in young iii) High mortality in young iv) Low mortality in adults v) High mortality in adults a) i b) iii + iv c) ii + iv d) ii+v 35 Type 1 survivorship curve shows: i) Constant rate of decline ii) Low mortality in young iii) High mortality in young iv) Low mortality in adults v) High mortality in adults a) i b) iii + iv c) ii + iv d) ii+v d) ii + v 36 Uniform spacing patterns in birds such as the black-browed albatross are most often associated with ________. A) patterns of high humidity B) competitive interaction between individuals of the same population C) the concentration of nutrients within the population's range D) the random distribution of seeds 37 Uniform spacing patterns in birds such as the black-browed albatross are most often associated with ________. A) patterns of high humidity B) competitive interaction between individuals of the same population C) the concentration of nutrients within the population's range D) the random distribution of seeds B) competitive interaction between individuals of the same population - for the albatross it is competing for nesting space as far as beaks will reach! 38 What is r in an exponential growth model? A)Intrinsic growth rate B) Logistic growth rate C) Population at time 0 D) Change in time 39 What is r in an exponential growth model? A) Intrinsic growth rate B) Logistic growth rate C) Population at time 0 D)Change in time A) Intrinsic growth rate (aka per capita rate of increase) N t = rN 40 When r is less than 0 which of the following is true? A)Birth rates are higher than death rates B) The population is stable C) Death rates are higher than birth rates D)The population is increasing 41 When r is less than 0 which of the following is true? A)Birth rates are higher than death rates B) The population is stable C) Death rates are higher than birth rates D)The population is increasing C) Death rates are higher than birth rates 42 Which graph shows a logistic model with a stable population? 43 Which graph shows a logistic model with a stable population? D) – It shows the population reaching carrying capacity (K) and levelling off 44