| Monitoring how populations change in size | Find effective ways of managing agricultural pests. Increase pop of rare, endangered species. |
| Population dynamics | Nnow = Nthen + B - D + I - E How pop changes over time
B= # deaths
D= deaths
I= immigrants
E= emigrants |
| Unitary organisms | Form, development, growth and longevity are highly determined and predictable. The zygote – from sexual reproduction –grows into a genetically unique organism |
| Modular organisms | Zygote develops into a unit of construction (a module) that then produces further, similar modules.
Immobile; often reproduce asexually. Genet: Individual produced sexually is a genetic individual. Ramets: Modules produced asexually from the genet. |
| How to determine pop size | 1. Count total pop - sometimes impossible so you estimate: Extrapolate; Pop size=densityxarea
2. Estimate the density |
| Sampling methods | 1. Use quadrats
2. Index of relative density
3. Mark and recapture technique. r/N = m/n
N= pop
r= sample is caught
n= sample recaptured
m= # marked in recapture |
| Reproductive effort | Objective is to maximise relative fitness. But extracts a cost to future reproductive success. NS optimises this trade-off |
| Species differ in their reproduction timing | Semelparous species: First they invest energy in growth and development, then have a single and distinct period of reproduction, after they die.
Iteroparous species: Repeated reproductive periods, they can be discrete or merge into a single period. |
| Basic Reproduction Number | R0 = Σ lxmx = ΣFx/a0 |
| Passive dispersal | Most plants, Non-exploratory, most seeds fall near parents, long range dispersal mechanisms: Wind, water etc |
| Active dispersal | Mobile animals. Maybe aided by passive means of transport. Range of factors can stimulate it: Crowding, food availability, temp |
| Migration | Mass directional movement of animals from one location to another and back again (a return trip).
Affect pop dynamics. Daily or seasonal migration. |
| What is competition | Is an interaction between individuals , brought out by a shared requirement for a resource. It leads to a reduction in a survivorship, growth and reproduction. |
| Population Biology: Concept 1 | Reproductive Rate R0 = Ng/ N0
N0= population time at0
Ng= population in the next generation |
| Population Biology: Concept 2 | Net reproduction rate RN= Nt/ N0
Nt= pop at the end of a time interval.
When R0=RN, the time interval equals one gen.
Pop growth when RN>1 |
| Intraspecific comp. | Results in an S-shaped pop curve |
| Pop growth in an unlimited env. | dN/dt = rN
dN= change in pop size
dt= over time
r= rate of change per individual (a constant)
N= # of individuals |
| Carrying capacity K | Availability of resources (food, space, water) will limit population growth. The carrying capacity (K) is the maximum population size that can be supported by its habitat. |
| Scope for population growth | K – N can be expressed as a proportion: (K-N)/K |
| Population growth in a limited environment | dN/dt = rN (K-N)/K |
| Logistic growth (model) | As the population grows, density dependent changes in birth and death rates take effect, so dN / dt
becomes zero. The curve is only an approximate for change of physical env, effects of predators, stochastic nature of birth/death rates. |
| Interference vs exploitation comp. | Interference: individuals Interact directly, comp intensity may be high
Exploitation: Do not interact directly, one individual is affected by the amount of resource that remains, comp intensity is linked to food availability. |
| The importance of density dependence | Many populations are at their carrying capacity. Competition depresses the growth and reproduction of
individuals; it also increases mortality. A density dependent process |
| 2 types of intraspecific comp. | Scramble: Growth and reproduction are depressed equally across individuals as comp increases.
Contest: Individuals deny their resources to others to share. |
| r and k species | r: colonise disturbed land, poor comp. have strategies to exploit short lived and changeable envs, rapid growth and fast dispersal.
k: low reproductive rate, good comp. Dominate in stable env, large and competitive species with slow pop. growth. |
| Different types of ecological interactions between 2 species | Predation: One party benefits, the other incurs fitness costs
Competition: Both parties suffer fitness cost
Amensalism: One suffers and the other neither loses or wins
Commensalism: One gains, the other neither loses or wins
Mutualism: Both parties benefit |
| Interspecific competition | Competition between individuals of different species for a shared, limited resource. Individuals undergo a
reduction in fecundity, growth or survivorship as a result of interference or resource exploitation. Minus-minus interaction |
| Allelopathy | A mechanism for interference competition seen in plants and microbes. Secondary metabolites that affect growth, survivorship and fecundity.
-ve allelopathy is important for interference comp: Plant compounds released into the soil inhibit growth of competitors. |
| Principles 1: Competition and asymmetry, | 1: Competition and asymmetry: Interspecific competition is often asymmetric, This can lead to 1 species excluding another through competition
2: Environmental conditions influence competitive ability
3: Competing species co-exist |
| Principle 2: Environmental conditions influence competitive ability | A mathematical model of interspecific competition. Expressions to describe the relationship between 2 species using the same resource. |
| Competitive exclusion principle | If 2 competing species coexist in a stable environment, they do so as a result of niche differentiation.
If there is no differentiation, or it is precluded by the habitat, one species will exclude the other.
Competitive exclusion occurs when the realized niche of the superior competitor completely fills the fundamental niche of the inferior competitor. |
| Invasive species | Non native species accidentally or deliberately introduced to an area outside of its natural range, which establishes and spreads and causes economic, environmental / ecological damage.
Reasons: The displace native species, damaging effects through predation and transmit pathogens. Native species do not have time to adapt. |
| Predation | Herbivores, Carnivores and Omnivores.
Predators are agents of mortality, with potential to regulate prey populations. |
| True predators | Invariably kill their prey by immediate attack, and consume several prey in their lifetime. |
| Methods of obtaining food | Ambush, Stalking and Pursuit |
| Grazers | Consume only part of each prey item. Do not usually kill prey, especially in short term. Attack several or
many prey in their lifetime |
| Parasites | Consume only part of each prey item. Do not usually kill prey, especially in short term. Attack one or very few prey items; form intimate association with their prey. |
| Predations affects: | Individuals: have high fitness cost on prey
Populations: regulate population of both predator and pop
Communities: som affect structure of communities |
| Lotka-Volterra prey equation | dN/dt=rN-aPN
a= search and attack efficiency
P= # of predators
N= # of prey |
| Lotka-Volterra predator equation | dP/dt=faPN-qP
P=# pf predators
N=# of prey
f= predator efficiency at converting food to offspring
a= search and attack efficiency
q= predator mortality rate
aPN= rate of food consumption |
| L-V model predicts mutual population regulation and assumptions | Prey increase when predator abundance is low, but decrease when it is high.
The converse is true for predators.
This density dependence is not direct but rather time-delayed
Predators have a max. feeding rate but model assumes not max.
Predator-prey pops do not exist as isolated pairs
Interaction influenced by env. |
| Ecological concepts: 1. Predator Functional Responses | Looks at effects on prey consumption of : predator satiation and ability to detect prey.
It describes the relationship between the per capita rate of prey consumption and the number or density of prey.
3 Basic Patterns: Type I. - The rate of consumption per predator is proportional to prey density (no saltation), passive predator.
Type II. - The rate of prey consumed per predator increases rapidly, then plateaus with increasing prey density, most common.
Type III. - S shaped curve: predator response to prey is depressed at low prey density. |
| Ecological Concepts: 2. Foraging for prey involves decisions about allocation of time and energy. "Optimal foraging Theory" | All prey do not offer the same energy. Predators must weight up the cost. Profitability: energy content-cost to acquire/time taken to acquire |
| Five Desicions | 1. Choosing between habitats. 2. Potential energy intake & need to avoid predators. 3. How long to stay in a
feeding patch? 4. Effects of competing predators in the same habitat. 5. What’s the optimal diet. |
| Other Ecological Concepts | 3. Predators influence prey through nonlethal and lethal effects
4. Physical conditions mediate predation
5. Infection can make hosts more susceptible to predation
6.Predator-prey interactions: a major evolutionary force: Predator-prey interaction is dynamic, Predators evolve efficient tactics for acquiring prey, prey evolve wide variety of methods of defence.
7. Predator prey populations don’t exist as isolated pairs |
