individuals and populations Flashcards
what is an ecosystem
interactions between abiotic and biotic elements
what is organismal ecology
concerned with behaviour, physiological and morphological traits that mediate interactions among individuals, between species and with the environment
what is a population
group of individuals of the same species living and interaction in a particular geographic area - these individuals compete for resources
what is population ecology
examines factors that limit and regulate population size and composition
what is a community
all the individuals of all the species that inhabit a particular geographic area
what is community ecology
examines the interactions among populations and how factors such as predation, competition, disease and environmental factors affect community structure and organisation
key processes that drive distribution and abundance
- colonisation
- birth
- death
- extinction
- emigration
- immigration
what is growth rate
change in numbers / time
- when 0 the population is not growing or shrinking but may still be changing within its equilibrium state
what happens when population densities are high
- population growth enters a negative feedback loop
- population growth rate will decrease due to other limiting resources e.g. food
what is ecology
- how many individuals are there?
- what kinds of individuals are there?
- where are they on the landscape?
- how and why do these numbers change?
what are unitary organisms
- have detrimental development
- easy to recognise genetically separate individuals
- strong programming means that local damages have serious consequences
- all animals look relatively similar
- easy to count
- e.g. mammals
what are modular organisms
- indeterminate development
- the genetic individuals start life as a zygote and does not follow a set developmental programme - therefore not predictable
- growth occurs by repeated production of modules
- the individual genet is not dead until all of its modules die - local damage is unimportant
- use biomass as an aggregate measure as to how much is there
what is population density
the number of individuals in a given area
how is the composition of a population divided
- how much as each age class?
- male to female ratio?
- juvenile to adult ratio?
- modular size
what is the life history theory
predicts how natural selection should shape the way organisms parcel there resources into reproduction and survival
what are key questions due to variation in life histories
- when do you start to produce offspring?
- how often do you reproduce?
- how many offspring is produced? (many small or few large)
key traits associated with variation in life histories
- rates (somatic growth and senescence)
- timing (maturation and frequency of offspring)
- allocation (offspring size and number)
simple life histories - ephemerals
- spend most of their life in a dormant state
- is an adaption to living in highly variable harsh environments - wait out the harsh in dormancy and take advantage of the good conditions
- when they emerge they reproduce rapidly and complete their life cycle within 8 weeks
what are ephemeral species
plants and animals whose whole adult lifespan only lasts a few weeks or months
- e.g. desert annual plants - dormant seeds
- e.g. some amphibia - dormant eggs
simple life histories - annuals
- adapted to seasonal environments to avoid harsh weather environments
- seasonal breeder and semelparous (die after reproduction)
- characterised by having 1 generation per year
- match their reproduction to when most resources are available
- spend part of their life in dormant stages (up to 100s y) with a fraction emerging each year
frequency of reproduction
can be iteroparous or semelparous
what is iteroparous reproduction
- reproduction is spread out
- produce offspring during reproductive episodes
- most mammals and some perennial plants and insects
what is semelparous reproduction
- big band reproduction
- large numbers of offspring produced in a single reproductive event
- the ‘mother’ dies soon after
- most annual plants and some perennial plants and insects
what is parity
the number of times a female has reproduced in their lifetime
look at lecture 2 for diagrams on life cycles and reproduction
Darwinian demon law
- an organisms that lives for hundreds of years, reproduces frequently and produced 1000s of offspring in each reproductive bout
how is the life history of an organism shaped
- shaped by natural selection to produce the largest possible combination of surviving offspring
- NS favours combinations of traits to maximise fitness
- however there is a trade off due to the principle of allocation
how can an individual maximise their fitness
- live a long time
- produce a large number of offspring at frequent intervals
what is the principle of allocation (LEWIS 1968)
each organisms has limits of the amount of energy that it can allocate for survival, growth and reproduction
- energy budget model
- energy is either allocated to somatic effort (growth, survival) or reproductive effort
constraints to Darwinian law
- Darwinian demons cannot exist because life histories are constrained by external factors (resources, competition, predators etc.) and trade offs among life history traits
- NS does not have a free hand to shape life histories because these constraints limits the range of options available
types of trade offs in life cycles
intra individual
- reproduction vs survival vs growth vs condition
- no. of offspring vs offspring size
- no. of offspring vs survival of offspring
inter generational
- parent survival vs no. of offspring vs offspring condition
what do conservationists need to understand
- how to predict extinction risk and time
- how to tell when a population is growing
- to know whether to save the babies or protect the adults
what does population age structure determine
- rate of mortality, reproduction and attributes
- this determines population behaviour
- from this scientists can infer things about the population - get an aggregate description
what is survivorship
describes how many individuals in a population are expected to survive to a specific age - this is denoted to lx
- what proportion of the population survives
survivorship curves
- plotting the log of survivorship proportion on the y axis against the x axis (time)
- y axis is a logarithmic scale
- always decreasing or nearly flat
- decline to 0 at a very high age when all individuals have died
types of survivorship curve (look at notes for diagram)
recognised according to their shape
- type I - high survivorship at a young to middle age then steeply decreases
- type II - linear decreasing line
- type III - decreases steeply at a young age then is relatively flat from middle to old age
what are life tables
- summarise births and deaths of organisms at different ages
- shows survivorship for different age classes
- 2 types cohort/generation and period (if world was constant both should be the same number)
cohort/generation life tables
- represents age specific rates over the lifetime of a cohort of organisms born during a relatively small period of time (proportional to their lifetime) - tracks them from birth to death
- usually used in ecology
- only includes females
- does not account for variability in births
period life tables
- represents age specific rates during a specific time period of a certain population
- reflects what happens in the past and future
what does lx stand for in cohort life tables
survival from age 0 to age x
what does Sx stand for in cohort life tables
survival from age x to age x+1 (any 1 year of life)
how to calculate Sx
= lx+1 / lx
- ratio of successive survivorship
what does Mx stand for in cohort life tables
mean number of offspring produced by each surviving individual over the age of x-1 to x
why are life tables useful
- contains useful information about the population and individuals
- enables you to calculate:
- net reproductive rate
- annual growth rate
- generation time
what is R0
net reproductive rate
- average number of female offspring produced by one individual female over her lifetime
- how much a population grows per generation
- a measure of fitness (lifetime reproductive success)
how to calculate net reproductive rate
R0 = sum of lxmx
Population change as a measure of R0
R0< 1 = population declines (females are not replacing themselves every generation)
R0>1 = population grows (have more than 1 female every birth)
R0=1 = stable population
what is generation time
- descriptor of the pace of life
- average time between successive generations
- calculated as a weighted average
how to calculate generation time
sum (Xlxmx) / sum (lxmx) = (Xlxmx) / R0
how does generation time affect population growth
a population with a shorter generation time but the same R0 will have faster population growth as there will be more births per unit of time
why is lambda used
to create a common scale when comparing population growth
- tells you how much a population per unit of time grows in the long run
- works as a multiplicative factor
how is lambda calculated
R0 to the power of 1/T
how are the transitions for life cycles diagrams derived
- survival rates probabilities
- per capita reproduction rates
semelparous life histories
organisms live for 3 years then die
iteroparous life histories
reproduces and survives at 3 years
- represented by a continuous circle/loop
what are matrix projection models used for
population projection to understand population change
phases in population growth
- initial transient phase (steep growth or decline)
- the long term constant growth/decline phase
why are matrix projection models useful
allow you to:
- calculate long term growth - understand whether a population will persists or go extinct in the long run
- look into the short term behaviour to predict the impact of different reintroduction strategies (focus on juveniles or adults)
what does r stand for
exponential growth rate
- uses the reference point of 0 instead of 1 like R
how to calculate change in population
delta N / delta t - bN - dN
(N=population size)
how would exponential population growth be achieved
- increase in proportion to birth and death rates
- have a population with few individuals
- is an environment with no limiting factors
- no restriction on energy availability
- no restriction on growth and reproduction
stable population equations
if b=d then r=0 then delta N/delta t = 0
what is logistic growth
combined exponential growth with the negative feedback of density dependence (causes the population to plateau)
how does density affect growth rates
- crowding and resource limitation
- affects both births and deaths
- individuals have to switch focus away from reproduction to their own survival as they have to prioritise their own health - thus per capita growth rates drop
- insufficient resources mean metabolic demands are not met which can lead to starvation and death
what affects carrying capacity (K)
- energy and resource limitation
- availably or territories and nesting sites
population limitation rules
