Reproduction Strategies
So, we discussed last time the difference between prey and predator, and how this impacts animal behaviour and physiology. Different species employ different strategies to ensure their species survives, and nowhere is that more apparent than in reproduction.
I know in school, lots of people spent this part of biology making crude jokes and stuff, but it really is a wildly interesting subject. No other system of living things is more varied than reproductive systems. Essentially every species has a different system. So let’s have a look at some examples.
Good at Multiplying – Rabbit Reproduction Strategy
A joke in Zootopia that probably went over most kids heads, but it’s well known that rabbits are good at making more rabbits. Does, female rabbits, reach sexual maturity between 3 and 8 months of age and can concieve at any time of the year for the rest of her life.
They are induced ovulators, meaning that the mating process causes the ovaries to release eggs. The gestation period is short, around a month. The young are born blind and helpless, and are kept in the nest underground, only feeding once or twice a day. She leaves them to feed.
The doe can get pregnant again the next day after giving birth. In theory, they can have 12-13 litters per year. With the young reaching maturity in a few months, it’s no wonder that left unchecked, rabbits reproduce exponentially. Just ask Australia!
I’m not joking, either. Rabbits were introduced to Australia and New Zealand by European settlers, and having no natural predators, they multiplied and are considered a huge pest due to damage done to crops. Infectious diseases were deliberately introduced to try to control their numbers.
So that’s one strategy – overwhelming numbers means that odds are, at least a few offspring will live long enough to reproduce. Even if there’s a high rate of mortality from predation and disease. It only takes a couple of buns to make more. So high reproduction rates ensure the species continue to exist.
Safety In Numbers – Herd Reproduction Strategy
Another common strategy is staying within the herd or flock. It’s rare to find prey species that live solitary lives. Most ruminants like deer, giraffes, cattle, goats and sheep will live in a large group or herd. This has a number of benefits for their offspring.
Firstly, more eyes and ears mean it is harder for predators to go unnoticed and sneak up on the group. If all the adult animals are keeping an eye out, the offspring will be safer. Young animals can stay near the group and will be harder to isolate.
These kinds of animals have young that are precocious, meaning they are quite mature at birth. Capable of standing, walking and running within hours of being born. They are born with their eyes and ears open. They are capable of keeping up with the adult animals of the herd if something happens.
Embryonic Diapause
You ever wish you could hit the pause button on life? Well, some animals can do that for developing embryos. Embryonic diapause means the mother can halt cell division in the blastocyst (a very early embryo) and delay implantation into the uterus wall.
Why would they want to do this? Often it is to ensure the offspring are born at the best time of year for factors like availability of food and temperatures. This gives the offspring the best possible chance of survival. Some species always have a period of diapause but for others it happens in response to day length and controlled by melatonin production in the pineal gland.
Species that have been observed to employ this strategy include marsupials such as kangaroos, bears, rodents and mustelids (weasels, skunks and badgers.) It is very common among insects, fish and other non-mammalian vertebrates.
Essentially the mother can pause the pregnancy or development of the embryo until it suits her better. Not something humans can really do but it is a good strategy for ensuring survival of the offspring.
Nests and Burrows
A common strategy in smaller prey species, hiding the offspring away in burrows or nests puts them out of reach of predators. The nest may be well hidden or defended by adult animals.
A lot of reptiles will bury their eggs. Sea turtles are a famous example of this. They go onto the beach, lay their eggs and bury them in the sand to keep them safe until they hatch. Once they hatch, the young ones must make the trek from nest to the water safely. This period of travel makes them vulnerable to predation of course, but they employ the overwhelming numbers strategy too.
Hiding evidence of newborn animals is another essential part of this. Contrary to popular belief, eating the placenta is a behaviour that has nothing to do with extra nutrition for milk production. Basically all animals that have a placenta do this, even herbivores.
So why? To hide the evidence of a newborn animal. That’s it. Simple as that. Giving birth is a messy business, there’s blood and amniotic fluid and stuff and it gets everywhere. Licking off the newborn and eating the placenta helps remove the scents and hide it.
Different Reproduction Strategies
So we can see there’s a few different ways that animals will endeavour to protect their young and ensure their survival. Direct parenting varies by species but it really depends on the environment and the predators in question.
Many prey species employ a few of these strategies. It’s really interesting to compare the differences, I think. Being able to pause development to ensure the young are born at the optimal time of year is really clever. Hiding young away, or keeping them safe within a large herd. Just reproducing at high rates, like rabbits do.
Of course, if you are creating your own creatures, you should consider this factor. How often do they reproduce and how to they ensure their offspring survive long enough to reproduce themselves? Bottom line is the need for survival of the species, so you need to have an idea how they approach this.
Thanks for reading, I hope you found this helpful. As always, any questions or thoughts, leave them in the comments. If you want some advice or help working through ideas, I’m happy to be of assistance. Subscribe to see more like this, and find me on my social media channels for behind the scenes.
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