These notes have been made using The Answer Series Part I and II. The notes have been made for the use of IEB students. These notes include all that is needed for IEB Finals in Life Science - HOWEVER, these notes should not be used in isolation but rather in conjunction with various other sources a...
Reproductive Strategies:
Successful reproduction is essential to ensure the continued existence of a species.
Animals use various reproductive strategies to increase their reproductive success.
Strategies are structural, functional and behavioral adaptations that increase the
chances of fertilization and survival of offspring.
The success depends on how a species utilizes energy to produce and care for viable
offspring.
There are 2 types of reproductive strategies:
R – strategy = spend too much time reproducing, not for parenthood. Thus
many of the offspring die before adulthood.
K – strategy = produce less offspring but spend copious amounts of time in
parenthood, thus the offspring have a better chance of surviving to
adulthood.
The following reproductive strategies are discussed:
1. Courtship.
2. External vs Internal Fertilization.
3. Ovipary, Ovovivipary and Vivipary.
4. Amniotic Egg.
5. Precocial and Altricial Development.
6. Parental Care.
Survivorship Curves:
Type 1 (convex curve):
High survivorship/low mortality in young individuals.
Low survivorship/high mortality in old individuals.
Type 2 (straight line):
Steady survivorship/steady mortality at all ages.
Individuals have the same chance of dying at any age.
Type 3 (concave curve):
Low survivorship/high mortality in young individuals.
High survivorship/lower mortality in old individuals.
Courtship:
Reproductive Strategies – Adapted from the Answer Series Part II
, JFIN 2019
Courtship is the behavoural patterns of male and female animals that lead to mating
and offspring.
The purpose of courtship:
Ensures both sexes are ready for mating.
Helps to identify mating partners of the same species and thus prevent
unsuccessful mating between different species.
Helps choose a suitable partner – females choose larger, stronger and more
attractive physical features for a male.
Courtship can take place by using:
Visual stimuli.
Sound stimuli.
Chemical stimuli.
Physical movements.
Visual Stimuli:
Best know example is a male peacock who uses his striking, brightly coloured tail
feathers to court the female.
Sound Stimuli:
Male frogs use sounds to attract the females. Each frog species has its own call.
Females make no sounds, but are attracted by the males calls.
Male birds also sing to attract females.
Chemical Stimuli:
In some insects and mammal species, the females secrete chemical substances
(pheromones). This is a signal to males that they are sexually mature.
Male moths can detect pheromones over long distances.
Female lions, dogs and cats also secrete pheromones in the air.
Physical Movements:
Scorpions perform a mating dance to ensure both sexes are ready to mate, if the
dance is successful, mating will occur.
Male tortoises ‘massage’ the females head, cheeks and neck with vibratory
movements of their long front claws.
Some male eagles perform acrobatics to impress females – flying high, dives down
and somersaults.
The male weaverbird builds a nest to impress the female, when the female
approaches, he will flutter around to display his colourful wings.
External vs Internal Fertilisation:
Fertilization – the fusing of a haploid male gamete (sperm) with a haploid female
gamete (egg/ovum) to form a diploid zygote.
Two types of fertilization:
External fertilization.
Internal fertilization.
External Fertilisation:
Takes place outside of the females body.
Reproductive Strategies – Adapted from the Answer Series Part II
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