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Reproductive strategies for Survival
How many, and how often?r Selection (aka. Quick-and-many)
K selection (aka. Slower and fewer)
Age of maturation Young – usually before the next breeding season
Older – usually many seasons after birth
Number of offspring
Many Few
Frequency of breeding
Usually frequently (many times a season) – high fecundity = many eggs produced per breeding season
Generally once a season. Low fecundity
Size of offspring Usually small Generally larger
Mortality rates High – many offspring do not live to sexual maturity
Low – offspring generally survive
Examples of species
Mice, rabbits, most insects, cane toads, octopus, mass spawning organisms
Humpback whales, elephants, humans, some birds
Eggs or liveborn young?Oviparity Viviparity
Literally means Ovum = egg, parus = bearing
Vivus = living, parus = bearing
Description Eggs released by mother, embryos develop outside mother’s body, nourished by egg yolk
Embryo develops in mother, born as young. Mode of nutrition varies
Benefits Reduced energy use in care of young
Yolk provides good nutrient source
More likely for offspring to survive to birth
Drawbacks Eggs may need to be incubated
Less chance of survival to birth due to eg. Eggs desiccating, predators, poor environment
Energy expenditure for female carrying offspring
Examples Birds, sharks, reptiles, monotremes
Humans, some snake species, most mammals
OviparityBony fish and frogs
Birds and reptiles
Known as - Amniote eggs
Shell None, or leathery membrane
Usually a hard, calcerious shell
Benefits Wedge into safe crevices
Better protected from desiccation – do not have to reproduce in water
Dangers Desiccation
Damage
Cannot be hidden in crevices
Examples Port Jackson shark, amphibians
Hens, monotremes, crocodiles
ViviparityTypes of viviparity are recognised by the nutrient source for the developing embryo
Egg yolk viviparity
Placental viviparity
Other source of nutrient
More notes Cool habitat – kept warmer within body
Largish eggs
Any – nutrient sent via blood stream to embryo
Very small eggs
Feed them unfertilised eggs
Feed them “uterine milk” – secretion from uterus
Examples Some sharks and snakes. Sea snakes – so that they do not have to return to land to breed
Mammals except monotremes, hammerhead shark
Porbeagle shark (feeds with eggs), Bat rays (feed with “milk”)
Activities
Glossary: r selection, K selection, fecundity, oviparity, viviparity, amniote, placenta, mortality, monotreme
Quick check questions: pg 383, 387.
Parental care or not?No parental care
Care of laid eggs
Care of young
What is it? No contact with offspring after eggs are laid
Guarding and/or incubating eggs to hatching
Care of young after hatching/birth
Benefits Free to mate more
No energy expenditure
Eggs have protection from predators/ harsh conditions
High chance of offspring survival
Drawbacks High levels of mortality
Energy expenditure
Some mortality after hatching
Very high levels of energy expenditure – may not be able to mate for many years after offspring birth
Examples Reef fish, frogs, turtles
Seahorse, diamond python, cephalopods (eg. Octopus, squid), spiders
Humans, primates. Mammals (milk), emperor penguins, emus
Case studies – 1. Australian Mallee Fowl
Male invests energy into nest building – incubation mound made of rotting plant matter
Female invests energy into laying 12 to 24 eggs at once
Male incubates Chicks hatch, do not
require further care
Case studies – 2. Emu
Polyandrous Male is caregiver He builds nest,
incubates eggs, guards young
Female lays eggs and leaves to mate again
Case studies – 3. Australian Marsupials
Australian Marsupials
Placental mammals (not marsupials) have a long period of uterine development
In contrast, marsupials have a short period within the uterus, and a long period developing in the pouch
TURN TO PAGE 391 IN YOUR TEXT BOOK
Australian Marsupials – arrested development Kangaroos and wallabies can suspend
development within the uterus If kangaroo conceives while young is in
pouch, she stops uterine development until pouch young is off the nipple in the pouch.
Activities
Glossary: cephalopod, marsupial, placental mammal
Quick check pg 393