ECOL20003NOTES

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ECOL20003 NOTES

Lecture 2: Habitat, Environment, Niche

‘Ecology is the scientiﬁc study of the distribution and abundance of organisms and the interactions that determine distribution and abundance’

(Essentials of Ecology textbook) Pattern → process → prediction

Habitat: a description of a physical place, at a particular scale of space and time, where an organism either actually or potentially lives.

- Can exist or be described without reference to an organism

Environment:the biotic and abiotic processes that interact with an organism - Resource: can be consumed - affects access by another organism

- Condition: physicochemical features - does not affect access by another organism. Eg.

temperature, wind speed, water flow, pH, relative humidity

- Resources and conditions can be stimuli (for growth, reproduction)

- Organisms can modify and, in a sense, create their environments through their behaviour, morphology and physiological processes

Niche:a subset of those environmental conditions which affect a particular organism, where the average absolute fitness of individuals in a population is greater than or equal to one.

- Niche dimensions are a subset of environmental dimensions, comprising only those that affect fitness

- Niche is defined by organism, because specificities of organism dictate which environmental conditions are relevant

- Fundamental niche: niche dimensions excluding biotic interactions (competition and predation), resulting in absolute fitness either equal to or greater than 1

- Realised niche: niche including biotic interactions. Usually smaller volume than fundamental niche

- A niche is an idea: a summary of an organism's tolerances and requirements. It dictates how, rather than justwhere, an organism lives

Fitness Performance

Environmental response curves

Environmental tolerance (performance vs. variable) - Temperature: extremes vs tolerable zone.

- Arsenic concentration

- Sodium: essential, but toxic at high concentrations Essential vs. substitutable

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Substitutability: whether resources can be replaced Degrees of substitutability

Liebig’s Law of the Minimum: growth is dictated not by total resources available, but by the scarcest resource (limiting factor).

Niches

- 1, 2, 3 dimensions (variables) - The n-dimensional hypervolume

- Requirements for an organism to sustain population Patch dynamics

Lecture 3: Niche

3.3, 3.4, 3.5

Niche: organisms partition an environment between them Abstract environmental space

Facilitation: when one species makes an environment more suitable for another species.

Possibly allowing the second species' realised niche to exist outside of the fundamental niche.

Dispersal theory: it is worthwhile to disperse because there is a chance that they will find a better suited location. All organisms have dispersal.

Therefore dispersal will lead to organisms also ending up in places where they are not suited.

Out of phase explanation: location was once suitable but is no longer

Dispersal limitationsandsource-sink dynamicslead to mismatches between suitability and occurrence of organisms across space.

- Source-sink dynamics: habitat quality varies for different organisms. If organisms are inhabiting a high quality habitat, then they might experience greater reproductive success. Excess organisms from that population may move to a different, lower quality habitat. Despite the habitat being unsuitable, a population may be able to persist there due to continual influx from the better quality habitat.

Imperfect knowledge of environmental gradients impedes the modelling and mapping of species distributions.

Plants and Resources

Plants require:

- Solar radiation

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- Carbon dioxide

- Mineral cations from soil

- Water and dissolved anions from soil Radiation

- Rate of photosynthesis increases with the intensity, to a point at whichphotoinhibition may occur. High levels of radiation may also lead to overheating plants.

- Constant variation in the angle and intensity of solar radiation that reaches a plant - diurnal cycles, shadowing, clouds, water

- Many trees produce different types of leaves: sun leaves, thicker high in the canopy and packed with chloroplasts to capture more light; and shade leaves which are flimsier and lower in the canopy, to supplement the photosynthetic action of the sun leaves.

- Herbaceous plants tend to be sun or shadespecies

- Some plants can have sun or shade leaf architecture depending on where they grow, to maximise photosynthetic activity while avoiding photoinhibition and self-shading

Water

- Absorption of CO₂through stomata inevitably results in loss of water vapour.

- If the rate of water absorption through the soil falls below the rate of transpiration from leaves, then the plant may dry out - cells lose turgidity and the plant wilts.

- To survive dry conditions plants areavoidersortolerators. Avoiders have a short lifespan and concentrate photosynthetic activity when they can maintain positive water balance, spending the remainder of the year dormant as seeds. Tolerators produce long-lived leaves that transpire slowly (possibly with less stomata), reducing the rate of

photosynthesis but also of water loss.

- CAM and C4 photosynthesis occurs often in plants living in arid regions, as they are more economical with water use.

- Roots have root hairs which closely contact soil particles. As roots draw water from the soil they create water depletion zones, or RDZs (resource depletion zones). The faster the plant absorbs water through soil, the more sharp the RDZ will be and the longer it will take for water to replenish the area.

Lecture 4: Population Dynamics

Change in population size = births - deaths + immigrants - emigrants Time models:

- Discrete: data only at specific times

- Continuous: data at any time over a period Exponential growth:

- Occurs when resources are unlimited

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- Often when a species is introduced to a new environment, or when recovering from a limiting factor

Population change = births - deaths dN/dt = B - D

= (b-d)N

= rN d = change B = births D = deaths b = birth rate d = death rate N = population size

r = intrinsic rate of increase

dN/dt = rate of change of individuals N over time

If r is above 0, the population will increase exponentially

To predict the size of a population after an amount of time, use the following equation:

e = 2.718 Equilibrium

dN/dt = 0 when N =N Model Assumptions

- Constant growth rate (no change in r) - No differences between individuals

- Closed population (no immigration or emigration)

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Limits on exponential growth:

- Density-dependent - Density-independent 5.1

Populations

It can be hard to conceptualise the ‘individual’ of a population when talking about modular organisms (eg. plants, marine invertebrates etc.). Organisms that have indeterminate growth are made up of ‘modules’, which grow and branch out throughout the individual's life. It is useful to distinguish between the ‘genet’ (genetic individual) and the module. “The genet is the individual that starts life as a single-celled zygote and is considered dead only when all its component modules have died. A module starts life as a multicellular outgrowth from another module and proceeds through a life cycle to maturity and death even though the form and development of the whole genet are indeterminate.”

Lecture 5: Density Dependence

Negative Density-Dependence:negative feedback between the population size and per capita growth rate.

Eg. Higher population numbers often lead to a decreasing intrinsic rate of increase.

Logistic population model:births might decrease and deaths might increase as resources become scarcer (in opposition to exponential growth model)

Carrying capacity (K): density at which the population stops growing Limits on population growth:

- Intra and interspecies competition, predation, parasitism - Human impacts

- Environmental variability Density dependent factors:

- Limiting resources - Infectious diseases - Predator explosions - Parasites

- Toxic by-products Competition over resources

Asymmetric and typically density dependant

- Interference competition (prevention of access) - Exploitative competition (prior use of resources)

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Equation for Logistic population model:

Unstable equilibrium: ones that can be easily disrupted (N=0)

Stable equilibrium: after small shocks population tends to return to equilibrium (N=K) H (harvest rate)= Rate of removal from population

Maximum sustainable yield= if harvest is higher than this rate, species will go extinct If harvest rate is lower than maximum sustainable yield, than equilibrium will be maintained Growth rate < harvest rate = population size declines

Growth rate > harvest rate = population size increases Assumptions:

- No variability in environment - No effects of chance

- Does not consider population structures or variation within population - That population growth can adjust instantly to changes

*scientists more often study small organisms