This preview shows page 1. Sign up to view the full content.
Unformatted text preview: Announcements:
•Mistakes found in syllabus for course Mistakes (timing of exam2, timing of final, missing reading)
•UPDATED SYLLABUS posted on gauchospace •Room changes for section also posted •BRING CALCULATOR TO SECTION THIS WEEK Recap key concepts lecture 4. Recap What are problems with assigning causation to What species traits ? Why does ‘habitat’ not perfectly predict species Why distributions? Define concept of ‘population’. Discuss difficulties with the definition. What are some of challenges associated with What ‘counting individuals’? ‘counting Sessile unitary individuals Sessile colonial individuals Mobile individuals (virtually always unitary) Lecture 5: Population biology/ecology Population
Assessing population status HOW ? WHY IS THIS INTERESTING ? WHY Are populations stable ? Are rare populations heading towards extinction ? Are pest populations increasing ? How fast do particular species recover from perturbations ? What factors limit population growth ? Goal= to assess status of a population and project into future…. population 1. Cohort life table analysis 2. Static age structure analysis 1. Cohort life table analysis 1. Must divide up life cycle into meaningful Must ages or stages ages Follow cohorts of individuals through Follow stages stages Evaluate survival from one stage to Evaluate another another Evaluate reproduction in each stage To project population change, start with a known # of individuals start Life stage % survival Between year 1 and year 2, population SHRANK Figure 5.8, Townsend Couldn’t you just have counted adults in each generation and come up with this information? What is the advantage of a stage based What survivorship analysis ? Identify critical or vulnerable parts of life cycle….. of Where are the problems ? Are these likely to persist ? Were causes of pop. shrinkage Were stochastic? stochastic
(Stochastic = random…e.g. bad weather, random appearance of a predator ?, random disturbance ?) Where are critical transitions that Where are reducing population growth ? are Is there any way that a management action could enhance survival ? Maybe need more information on life stages and critical age classes stages (esp. important for long-lived species): (esp.
? Young ? ?
Yellow bellied marmot Old adults Middle aged Which stage is contributing Juveniles most to population change? Where is mortality highest ? Young adults Follow cohort or multiple cohorts through each stage, Follow calculate average survival and fecundity calculate
? Young ? ?
Yellow bellied marmot Old adults Middle aged Juveniles Young adults LIFE TABLE ANALYSIS: TABLE 5.2 TEXT BOOK Ro = overall extent that population has increased or decreased in a generation increased
if Ro= 1 , no change if < 1, declining 1, > 1, increasing LIFE TABLE ANALYSIS: * TABLE 5.2 TEXT BOOK * = most fecund MARMOT LIFE TABLE CONCLUSIONS : CONCLUSIONS Population is declining with a net reproductive Population rate < 1 rate Females ages 2-4 contribute most to population Females growth although females age 8-10 are most fecund fecund High mortality going from first year to second High year = important source of low net population reproduction Enhancing female survival to age 8-10 would increase Enhancing population growth population MARMOT LIFE TABLE CONCLUSIONS : CONCLUSIONS Old individuals (11-15) do not contribute to Old population reproduction/replacement population Are they important in other ways ? (alarm Are calls? Exploration for food sources ? Protection in burrows ?) Protection Do they compete with young for food ? Do Age/stage structured analyses tell you a lot but it can be challenging to get accurate data to Difficult to know age of individuals Difficult to identify and follow cohorts Individuals may disperse temporarily but Individuals not be dead Immigration may occur into populations so Immigration new individuals show up in age classes that didn’t start there that Usually there are overlapping cohorts Measure multiple cohorts and take average Measure values Plants—wide range of life cycles Annuals iteroparous perennials
(Flower and fruit over many years) Semelparous perennials (Die after ONE flowering)
Biennials Unlike animals, fertilized ovules of plants do not have to become young plants for many years young Can live as dormant (sleeping) seeds in Can soil or on the plant itself soil Most species have some sort of dormancy Seed bank = seeds dormant in soil or dormant in structures on plant or Soil = full of sleeping seeds that can be woken up when conditions are right Many generations of seeds can be stored on some trees Seed banks Seed Can buffer a population against local Can extinction extinction Can store genetic variation for a Can population or species population Can be a means of surviving harsh Can periods (e.g. desert annuals) periods CAN MAKE IT more challenging to predict CAN population trends if you don’t understand germination requirements germination Population prediction = dependent on weather LIFE TABLE ANALYSIS for plants: Simplified life cycle Simplified
germination pollination seed set Reproductive (adult)
Growth & flowering Seedlings growth Pre-reproductive (Vegetative stage) Seeds pollination seed set Reproductive (adult)
Growth & flowering germination
growth Pre-reproductive (Vegetative stage) To project population growth what do you need to know ? do Average # of seeds germinating from seed Average bank bank Survival between stages Reproductive output from each stage Obtain averages for the population Put into life table Classic study in your text Classic Annual plant: Phlox drumondii Annual Phlox
Cohort analysis = easiest for annual species If there is no seed dormancy, will next generation be bigger or smaller than this one ? Evaluating vital rates…. vital Imagine you are a manager…where are Imagine key transitions that could greatly change population size ? population What might you do ? Plot lx (proportion surviving) data –create survivorship curve…. (Fig. 5.11, TEXT) MOST individuals are lost early Marmots Early cohorts had more in them, decline from 1.0 looks more dramatic YET probability of surviving interval =same for the individual Log scale accounts for early decline appearing bigger than later despite being same reduction in individual probability of survival Plot lx (proportion surviving) data –create survivorship curve…. (Fig. 5.11, TEXT) Marmots, risk of mortality relatively constant across ages between 1-10 Phlox, high early mortality …then higher survival Why do we use log of lx on y axis ? Why If the reduction across intervals is same If (proportionally) then it will appear same with log value How would you manage marmot population to keep it from declining? Assessing population status Assessing 1. Cohort analysis 2. Static age structure analysis ⇒ Plot fraction of population in each age or size class at one time (=static)
Fraction of population
Rapidly growing Not replacing itself population is likely in decline Age Lots of youngsters….project rapid growth Mostly old folks…..project decline End here End ...
View Full Document
- Fall '08