Population Ecology - Lecture notes 20 PDF

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Dr. Daniel Stern Cardinale...

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Population Ecology Tuesday, November 29, 2016

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9:11 AM

Intro ○ CC major concepts Population growth ○ CC 2 growth models Life history ○ CC life history strategies Population size ○ CC factors driving population size

Intro a. Basic concepts i. Ecology- the study of interactions between living organisms and physical environment ii. Population-group of potentially sexually interbreeding organisms of the same species living in the same area at the same time-share same gene pool, affected by selection, drift etc. iii. Individuals within populations 1) Rely on and compete for same resources 2) Influence by similar environmental factors 3) Population ecology-considers number of individuals in an area and population dynamics 4) Population dynamics- study of change in populations 5) How and why population size changes over time 6) Processes common to all populations 7) Different features of populations iv. Population size 1) Number of individuals 2) Meaningful only when considered within specific areas v. Population density 1) Number of individuals per unit area or volume at a given time 2) Varies based on scale

b. Changes in population size i. All populations have potential to increase or decrease in size ii. Changes- births + immigration - deaths - emigration iii. Changes in pop over time iv. Births (B) deahts (D) v. N-pop size vi. T-time vii. deltaN/deltaT=B-D viii. The change in population over a time interval is the difference between the number of births and the number of deaths in a populating over that time ix. Expressed as per capita change 1) Per individual changes per unit time x. Birth rate 1) A b-per capita birth rate; # offspring produced per unit time by average individual in pop 2) B=bN--> expected number of births per year in pop size of N xi. Death rate 1) m-per capita death rate,, likelihood of death per unit time by average individual in pop 2) D=mN xii. ∆N/∆t=bN-mN xiii. N/Jt=N(b-m) xiv. Most interested n difference between per capita birth rate and per capita death rate xv. ∆N/∆t=rN 1) R=rate of increase xvi. Possible situations 1) R,)--> population shrinking 2) R>0--> population growing 3) R=0--> no net change a) Birth and deaths are occurring, but balance out, dynamic equilibrium xvii. Population growth expressed instantaneously 1) Want to know growth at specific moment, rather than change over an interval 2) Over interval, we can divide ∆N by ∆t 3) Instantaneous--> ∆T=) iii W d i i

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xviii. We can use derivatives 1) dN/dT=rinstN a) Rinstantaneous-instantaneous rate of increase 2) Rinst x population size (N)-instantaneous change in population size xix. Intrinsic rate of increase 1) Rmax-maximum rate at which population could increase under ideal conditions 2) Abundant resources 3) Low density 4) Micro organisms have highes rmax 5) Large organisms tend to have low rmax Population growth models a. Exponential growth model i. Every member of population has access to abundant resources ii. Free to reproduce as physiological capacity iii. Population growing at rmax iv. Rinsta=rmax v. Will likely not grow exponentially vi. J shaped curve b. Logistical growth model i. Considers environment resistance ii. Growth rate slows as population reaches limit iii. Carrying capacity (K) 1) Largest population that can be maintained for an indefinite period by a particular environment 2) Assumes no change in environment iv. Logistical growth curve 1) Sigmoid or S-shaped curve 2) Starts as exponential 3) Slows as N approaches carrying capacity v. Logistical growth model equation 1) dN/dT=rinst((K-N)/K) 2) 1st part describes exponential growth 3) 2nd part reflects slowed growth as N approaches K 4) If you have a very small in (2nd part) it will be close to one--> rapid growth 5) Large N, it will be close to 0--> slow growth 6) When N=K no growth population is stable

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6) When N K, no growth, population is stable vi. Generaly more realistic 1) Compared to exponential model 2) But perfectly logical curves are rare 3) Populations tend to fluctuate around K 4) Environments never completely stable--> K may change 5) --> most populations fluctuate around some mean vii. Realistic logistic model 1) Pop < K, pop grows 2) Pop >, pop shrinks Life history ○ Ways in which organisms maximize survival and reproduction a. Many strategies i. Often trade offs between survival and reproduction ii. 3 main variables 1) Age at first reproduction 2) Frequency of reproduction 3) # offspring per reproductive episode iii. Natural selection will favor strategies that maximize evolutionary fitness iv. Semelparous 1) 1 large reproductive event 2) Insects, plants, fish 3) Favored in species with a) Low survival rate for offspring b) Highly variable environment c) High adult mortality v. Iteroparous 1) Reproduce many times 2) Most vertebrates, many plants 3) Favored in species with a) Stable environment b) Low adult mortality c) High competition vi. Timing of reproduction 1) Involves tradeoffs 2) Reproduce early a) E towards offspring instead of own growth b) May reduce survival

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Reproduce late a) E towards growth--> higher survival b) Less E towards offspring

b. 2 extremes i. R-selected species 1) R selection 2) Producing many offspring fast 3) High population growth rate, close to r max 4) Tendency towards a) Small body size b) Early maturation c) Large broods (many offspring per reproductive episode) d) Little or no parental care e) Short life span 5) Variable and/or temporary environments 6) Low probability of long term survival 7) Only works with a high r ii. K-selected species 1) K selection a) Few offspring, high parental investment b) Population size close to K most of the time 2) Tendency towards a) Long life b) Slow development c) Older at 1st reproductive episode d) Low reproductive rate (low r) e) High parental care f) Large body size g) High competitive ability h) Better defenses 3) Favored in stable environments 4) Higher probability of long-term survival 5) Maintains relatively stable N close to K iii. Which strategy is better? 1) Depends on environment 2) Both are common, so both are selected for in some cases Factors influencing population size a. Density independent factors i E i t lf t th t t ith t l ti t l ti

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Environmental factors that operate without relation to population density ii. Tend to be abiotic iii. Natural disasters iv. Weather v. Resources-K is independent of how many are present vi. Birth rate and death rate do not change with density (usually) b. Density dependent factors i. Environmental factors whose impact on population is affected by populations density ii. Change in density changes affect on population in general, act as negative feedaback system iii. Higher density--> greater effect--> pop shrinks--> lower density--> less effect--> pop grows--> higher density iv. Generally leads to stable population size near K v. Tend to be biotic 1) Competition for resources 2) Predation 3) Disease 4) Toxic wastes c. Realistically a combination i. Of density dependent and density independent factors affect population size in most species ii. As in all things, rarely one single explanation Summary Changes in population size Populationg worht dynamics and models...