BIOL 2390 - Topic 7

Life history

Refers to an organism’s strategy for growth, survival, and reproduction

Shaping life history

It is not necessarily a conscious choice, but rather strategies that have been shaped by the environment and biological interactions throughout the organisms evolutionary history

Resources effect on life history

There are limited resources available, therefore they have to allocate it carefully among their life tasks, such as for…

1.) Growth

2.) Development

3.) Gathering food

4.) Reproduction

Dividing resources among offspring

It impacts their survival and success

2 types of reproduction

1.) Asexual reproduction

2.) Sexual reproduction

Asexual reproduction

It is basically just cloning, as it produces genetically identical offspring, which are well-suited for stable environments

Asexual reproduction advantages

1.) It eliminates the need of finding a mate, allowing for faster reproduction

2.) As a result, this can lead to rapid population growth under favourable conditions (i.e. as long as resources are available)

Asexual reproduction disadvantage

1.) It reduces genetic diversity, which limits its adaptability to environmental changes

2.) Therefore, there’s a chance that the entire population can get wiped out due to a uniform response

Sexual reproduction

It produces genetically unique offspring, thereby improving adaptability to environmental changes

Sexual reproduction disadvantages

1.) Only half of a parents’ genes are passed to an offspring, therefore assessment of partner is very important

2.) It requires specialized organs and time/effort into finding a mate

Reproductive costs of sexual reproduction

It involves significant, often unequal, reproductive costs, such that most of the responsibility falls on the female

Mating systems

Refers to the patterns of mating between males and females in a population

Different mating systems

1.) Monogamy

2.) Polygamy

3.) Promiscuity

Mating systems are usually ________ specific

Species

Monogamy

A mating system where a pair bond forms between one male and one female, which either lasts for a life-time or during each season (seasonal monogamy)

Role of organisms in monogamy

Both the parents provide food, warmth, and protection to the offspring (not just one)

Advantage of monogamy

It increases the fitness for both parents, by sharing the burden of caring for the young

Changing partners in monogamy

This usually only occurs if their first partner dies

Monogamy in mammals

It is rare, because females can lactate and males cannot, therefore males often contribute very little to the offspring’s survival and would benefit more by mating with multiple females

When would mammals be monogomous?

When males have additional roles, such as defending the young and nursing females (ex. beavers)

Polygamy

When an individual acquires two or more mates and therefore they are all bonded together

Two types of polygamy

1.) Polygyny: when a male is mated with multiple females (such as lions)

2.) Polyandry: when a female is mated with multiple males (such as sandpipers)

Role of harem leaders

They typically do not care for the young and instead focus on competing for mates and controlling high-quality resources

Harem leads competing for mates

Others are constantly trying to outcompete them to be the leader of the harem

Harem leaders often have…

They have strong sexual dimorphism, such that they possess traits that helps them perform their jobs better, such as having strength and being aggressive

Promiscuity

It is when males and females mate with multiple partners and have no lasting relationships (i.e. no harem)

Why does promiscuity occur?

1.) It occurs when males provide no care, protection, or territory for the offspring

2.) Therefore, neither females or males gain an advantage by staying with one mate

Promiscuity advantage

It increases genetic diversity within the population, because they are likely to mate with different individuals per year

Where is promiscuity seen?

It is often seen in animals who live in tough and challenging environments, such as polar bears

Darwin’s discovery of sexual selection

He observed traits was contradictory to natural selection, such that they seemed costly and impractical for survival and looked like it would likely get them killed more quickly

Impractical traits observed by Darwin that led him to sexual selection

1.) Elaborate plumage (feathers)

2.) Elaborate horns

3.) Large-sized polygamous males

What did Darwin’s sexual selection help explain?

It explained certain differences observed between males and females, in terms of size, ornamentation, colour, etc

Two types of sexual selection

1.) Intrasexual selection (within the same sex)

2.) Intersexual selection (between different sexes)

Intrasexual selection

Selection that favours traits for combat, such as large size, aggression, and combat traits (such as horns and antlers), therefore those that don’t have these strong traits are selected against

Where is intrasexual selection seen?

It is strongest in polygamous and promiscuous systems, but weaker in monogamy

Intersexual selection

It is when one sex, typically females, selects mates based on attractiveness

Attractive traits in intersexual selection

1.) It favours traits such as bright plumage, displays, or ornaments

2.) Sometimes it is not a physical trait, but the ability to perform a certain task, such as singing with warblers

Attractive traits indicate…

1.) It indicates that the individual has good genetic quality, health, and/or access to resources

2.) Those that don’t have the trait will therefore be seen poorly

Drawback to attractive traits in sexual selection

1.) Traits favoured by intersexual selection can be costly to maintain, as the attractive traits they possess usually acts as hindrances in regards to predators

2.) Ex. Peacocks have an elaborate tail that may prevent them from escaping predators

Intersexual selection causes…

Sexual dimorphism

Intersexual selection in Grouse

Males put on courtship displays by performing drumming, where they beat their wings to their chest, allowing females to select a mate

No sexual dimorphism indicates __________ mating patterns

Monogamous

Reproductive timing

Refers to the number of times an organism can reproduce over its lifetime

Two types of reproductive timing

1.) Semelparity

2.) Iteroparity

Semelparity

When an organism reproduces only once in its lifetime, usually after a long-term energy investment in growth and storage

Drawback of semelparity

They often reproduce at the expense of their future survival, such that they usually die after reproducing

Iteroperaity

Organisms that reproduce multiple times over a lifetime

Advantage vs. disadvantages of reproducing late

1.) You are more established and have most likely gathered enough resources to support the offspring

2.) But you might not be able to make it to be able to reproduce (i.e. may get picked off by a predator first)

Advantage vs. disadvantage of reproducing early

1.) Have a higher chance of actually reproducing before you get picked off by a predator

2.) But you may not have enough resources to support your offspring

Reproductive effort

1.) Refers to how much effort you put into reproduction and caring for offspring

2.) It varies widely among organisms

Balancing reproductive effort

You have to decide how much energy will go towards reproduction and how much will go towards survival and growth, such as tissue production, acquisition of food/territory, and predator escape.

Reproductive effort in plants

1.) Perennials: 15-20%

2.) Annuals: 25-30%

Why do perennials put less effort into reproduction

Perennials grow every year, therefore they have to invest some of the energy for themselves, to ensure they are able to survive throughout the year

Why do annuals put more effort into reproduction

They only live for a single year, therefore they are able to put more energy into reproduction, since they don’t need it for themselves

Why do crops have a much higher reproductive effort

Because we specifically drive them to have more reproductive effort

Reproductive effort in animals

1.) Common lizard: 7-9%

2.) Salamanders: up to 48%

Reproductive effort in homeotherms

They usually do not allocate as much as energy into reproduction, since they already burn so much energy into maintaining their body temp

Life history characteristics

They have evolved adaptations to environmental conditions, which have been shaped by natural selection

Life history characteristics in variable, short-lived environments with high disturbance

They have high reproductive effort, such that they favor reproduction and higher dispersal, because they may not be alive for very long

Dispersal

The ability to move from one location to another

Variable, short-lived environments

Environments with high unpredictability, as a result of natural or human events that leads to disasters, such as…

1.) Flooding

2.) Forest fires

3.) Highways

Life history characteristics in stable, long-lived environments with low disturbance

They have lower reproductive effort, such that they favor slower growth, delayed reproduction, and competitive traits, since they are more sure about being alive for longer

Stable, long-lived environments examples

1.) Tropical rainforests

2.) Coral reefs

Species adapted to stable vs. variable environments will differ in…

They will differ in life history traits, as they have been specialized by natural selection to survive in the environment they live in

Species adapted to stable vs. variable environments differing in life history traits

1.) Size

2.) Number of offspring

3.) Age of first reproduction

4.) Number of reproductions over a lifetime

r and K strategies

Refers to components of the logistic population growth model, which are shaped by different environments

K in the logistic population growth model

Referred to as the carrying capacity, which is the max number of individuals that an environment can carry

K-type species

They are near the carrying capacity, usually living in a stable environment

r in the logistic population growth model

Refers to the speed at which a population grows

r-type species usually live in…

They usually live in short-lived environments

r-strategists characteristics

1.) Short-lived with high reproductive rates

2.) Rapid development, with small body size

3.) Produce many offspring, with low survival and minimal parental care

4.) Exploit unstable, temporary habitats

r-strategists in their habitats

1.) They use resources quickly, as they are poorly adapted to stress

2.) Well-adapted for dispersal and colonization in disturbed areas

3.) Have quick maturation and early reproductions

r-strategists examples

1.) Weedy plants

2.) Rodents

3.) Insects

4.) Frogs

5.) Bacteria

K-strategists characteristics

1.) Long-lived, with low reproductive rates with populations near the carrying capacity

2.) Have slow growth, with large body size

3.) Produce few offspring, but provide parental care

4.) Exploit stable, long lasting habitats

K-strategists in their habitats

1.) They are efficient resource users, as they cope well with biotic and abiotic stresses

2.) But they are poor colonizers with slow, restricted dispersal

3.) They also have delayed, but repeated reproductions (i.e. wait for maturity and sufficient resources)

K-strategists examples

1.) Wolves

2.) Elephants

3.) Humans

4.) Birds

5.) Large trees

Can we compare mammals with mammals?

Yes

Can we compare mammals with insects?

No