Large females (1 Viewer)

ColinD

Well-known member

• Nov 23, 2003

• #1

Ok, now I've got your attention, here's something I haven't seen mentioned before, but which I've wondered about for a while. Why is it that when it comes to predators, the females are often larger than the males?

Here's a few examples:

1) in the majority of bird species the male is larger, but bird of prey females are larger than bird of prey males.

2) In the majority of mammals, males are bigger than females, but female big cats are bigger than males.

3) In fish, the majority of males are bigger than females, but female sharks and Pike are bigger than males.

4) female spiders are bigger than males.

5) according to Walking with Dinosaurs, female Tyranosaurus Rex was bigger than males.

I have deliberately chosen a diverse selection of species to emphasis the point. There are other examples I could give.

I suppose it doesn't always hold true, and I'm sure somebody can find a flaw in my arguement, but it almost seems that if the species is essentially a vegetarian then the males are bigger, but if it's EXCLUSIVELY a meat eater, then the female is bigger. Anybody got any comments on this, or have an explanation of why it should be?

Colin

 

L

logos

Well-known member

• Nov 23, 2003

• #2

Are female big cats really larger than males? I thought it was the other way around.

Spud

 

ColinD

Well-known member

• Nov 23, 2003

• #3

logos said:

Are female big cats really larger than males? I thought it was the other way around.

Spud

Click to expand...

Female lions are certainly bigger than males, but I'm not sure about other big cats.

However, even if it's just true of birds, why should female birds of prey be bigger than males, when in the majority of other bird species, the male is bigger?

Colin

 

Last edited: Nov 23, 2003

Michael Frankis

conehead

• Nov 23, 2003

• #4

Errrr . . . no . . Lions (average 170 kg) are definitely larger than Lionesses (average 140 kg)! Ditto for Tiger, Jaguar & Leopard, males larger.

In general, female raptors tend to be larger as they have to protect the young from the male, as well as other potential nest raiders. Female Sparrowhawks barely tolerate the presence of the male near the nest when the young are small, sort of "give me that prey, and then GET OUT OF HERE!!!"

Oh, and infanticide by male Lions is by far the largest cause of mortality among Lion cubs.

Michael

 

L

logos

Well-known member

• Nov 23, 2003

• #5

Michael is I'm sure partly right but the issue of reversed sexual dimorphism has been described as 'one of the most intractable problems in raptor biology' (Newton 1979). Many theories have been put forward why females are larger than males (including that given by Michael) and in reality it is probably a combination of factors that have led to this apparent anomaly - others include the fact that the males do much much of the hunting during the breeding season and small males will need less food for themselves, a larger female will, due to its larger mass, risk less damage to any eggs inside her when hunting, smaller males will take smaller prey which tends to be more varied and more easily transported to the nest than large prey etc etc...

A further interesting question relates to whether females have evolved to become larger or males to become smaller...

Spud

 

Jasonbirder

Jason-occasional-twitcher

• Nov 23, 2003

• #6

Part of the reason for the size differential is so as they don`t compete directly for the same prey when they are sharing a territory: they are able to target slightly different food items, avoiding direct competition.

 

Last edited: Nov 23, 2003

steve_nova

Well-known member

• Nov 23, 2003

• #7

I thought that the principle reason was to reduce direct competion on food resources ie the female will take different species to the male in the same local area so reducing competition while breeding?

 

steve_nova

Well-known member

• Nov 23, 2003

• #8

Snap!

 

seb_seb

Well-known member

• Nov 23, 2003

• #9

True Jason, but i think the question was why the female always larger?

 

steve_nova

Well-known member

• Nov 23, 2003

• #10

It may be that it appeared very early in the evolution of the order Falconiformes and simply translates itself through all the many species as female larger. It could though as Michael and Logos have mentioned be something to do with the female bird having to protect the nest site.
It could also be something to do with the larger the bird in relation to the egg size, the less of a handicap this extra weight would be while hunting. Selection would naturally favour the larger female perhaps?
It may well be more than just one factor as already suggested.

 

pauco

Старлин&

• Nov 23, 2003

• #11

Back to the big cats, the males are by far always
larger,thats why they let the female hunt i-e
they are to slow. But they always take the biggest share of the kill, even when cubs are in
the pride.

 

Andrew Whitehouse

Professor of Listening

Supporter

• Nov 24, 2003

• #12

In the interests of equality, can anyone explain why males are larger than females in many species?