Biol 121 notesEcology

Characteristics of a good pioneer species:

good dispersers can survive extreme abiotic conditions produce lots of offspring grow and mature quickly

Abiotic and biotic factors:

Abiotic factors are more important in earlier succession - because pioneered species can moderate a hostile environment

Biotic are more important in later communities - because species prominent here are usually better competitors

Fundamental niche – the resources used or conditions tolerated in the absence of competitors

Realized niche – the resources used or conditioned tolerated when competition does occur

Competitive exclusion principle – the claim that it is not possible for species with the exact same niche (tolerances & resources) to coexist

Symbiosis:

Commensalism - type of relationship where one of the organisms benefits greatly from the symbiosis. The other is not helped but is not harmed or damaged from the relationship. EX: a bird living in a tree

Parasitism - one organism benefits from the relationship but at the expense of the other. The organism may live inside the other’s body or on its surface. EX: Tapeworms: do more damage to their hosts because they eat partially digested food and that deprives the host of some food and nourishment.

Mutualism - a close relationship where both parties benefit. Both species will benefit from the relationship and many of these relationships are long-lasting. EX: Humans and microorganisms. Humans have a mutualistic relationship with microorganisms, primarily bacteria, in their digestive tract.

Disturbances – events which removes some individuals or biomass from a community – this then alters some aspects of resource availability for other organisms which depend on these organisms.

Pulse (short-term disturbances) – wind storms, floods, fires, new species arrival, disease epidemics

Press (long-term disturbances) – climate shift, extinction, mountain building, change in river channels, continental movement

Human disturbances – deforestation, surface mining, commercial agriculture

Primary succession – occurs when a disturbance removes the soil and its organism, as well as organisms living above the surface

Secondary succession – occurs when a disturbance removes some or all of the organisms from an area, but leaves the soil intact.

Population

Calculate rate of increase of a population: r = birth rate – death rate

Exponential Growth Equation: G = rN

G is population growth per unit timer is net rate of increaseN is population size

When population density gets very high, birth rate should decrease and death rate increase, causing r to decline. This type of growth is density dependent.

Carrying Capacity (K) - maximum number of individuals that can be sustained in a particular habitatLogistic growth occurs when population size is limited by carrying capacity.

Logistic growth is dependent on population size. Density dependence: Growth rate slows at high density.

Sociality can be considered an adaptation to the environment. When the environment is harsh, if some individuals stay at home and help care for offspring, they would survive and pass on their genes (and traits). Therefore, individuals that do not disperse will be selected for and overtime leading to permanent group-

living as an adaptation to the environment.

Sometimes not dispersing is better because an individual doesn’t have to risk predators, look for a new territory, or worry about finding a mating partner.

Social species are usually found in harsh or unpredictable environments and at lower latitudes and lower elevation.

Benefits of sociality:

Easy to capture larger prey because you are in a group rather than on your own There is a smaller chance for you to be eaten because there’s many of you in your group You will make a larger structured home for your group and that is harder to be damaged compared

to a small place of habitat built for your own use

Limiting factors: sunlight, water, nutrients such as nitrogen and phosphorus are needed for plants to grow. Plants compete for these limiting factors.

Ecosystems need large amounts of producers to sustain large amounts of consumers especially secondary or tertiary consumers, like bears for example.

Genetics

Factors to consider in pedigrees:

o Autosomal – not on a sex chromosome

o Sex Linkage – located on one of the sex chromosomes

o Dominant - the trait is expressed in every generation.

o Recessive - expression of the trait may skip generations.

X-linked recessive

- Females often carriers, more males affected- Does not pass from father to son- Affected female = all sons will be affected

X-linked dominant

- More females than males- Affected father – all daughters will be affected, but none of the sons

Other clues:

- If a trait skips no generations Dominant - If the trait is not seen in parents, but is seen in their children (at least one) Recessive- Unequal sex ratio Sex linked (on X chromosome)- If more males than females affected X-linked recessive- If more females than males affected X-linked dominant

Five conditions to allow for the Hardy-Weinberg principle:

1. The population is large enough that chance events will not alter allele frequencies.

2. Mates are chosen on a random basis.

3. There are no net mutations.

4. There is no migration.

5. There is no natural selection against any of the phenotypes.