Download PRIMATE MATING MAMMALS: reproduce sexually

PRIMATE MATING
MAMMALS: reproduce sexually - biology similar
Some - males compete with males
Others - female preference important
monogamous species: males and females care for offspring
non monogamous species: females care for offspring while males
compete with males to get other females pregnant
Humans? Biology like other primates
fathers contribute to children’s welfare extensively
Evolutionary forces shape reproductive strategy
Cost/benefit
Primates - K strategy of INVESTMENT
relative amount of care differs
MALES do not care for offspring when:
1. can easily use resources to acquire additional offspring
2. caring does NOT increase offspring’s fitness
MALES compete for FEMALES:
if females are difficult to locate
MALES stay and help care for the young:
If young not likely to survive without 2 parents investing
FEMALES: always invest in offspring
Pregnancy and lactation
Primates: Extended pregnancy - brain cells develop slowly
Infancy long - wean late
Each female - relatively few offspring
Mothers strongly committed to each offspring
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Females compete with each other for resources
Develop dominance hierarchy
Especially when food is clumped
High females get more food
High ranking females have greater reproductive success
Offspring of high-ranking mothers:
-more likely to survive weaning
-grow faster
-become high ranking
PRIMATE SOCIALITY
Most monkeys and apes live in social groups. WHY?
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ONE MODEL
Defend resources
Joint defense profitable when:
1. food is clumped in time and space
2. food is relatively valuable
3. enough food in clump to support several individuals
like FRUIT
1. grows in discrete patches/ ripe time dependent - clumped
2. easily converted to energy
3. lots at one time and space
many primates eat fruit- frugivores
Large groups defeat small groups – inter group competition
PROBLEMS with model
~trade off: INTRA group competition
~some species social, not eat fruit
~female fitness - some in group (low ranking) not as fit
~some eat fruit, not social
Reality is complicated!
ANOTHER MODEL
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Defense against predation
Groups reduce vulnerability
-ground groups more social and predation more of a risk
-large primates (least in danger) less likely to live in big groups
-young - higher mortality in small groups
-adjust behavior to risk
PROBLEMS with model
~some large primates live in groups
~predation VERY difficult to study
~don’t see more loss in ground groups
use BOTH models
OPTIMUM GROUP SIZE:
Predation -> more than bigger group
What eat -> fruit than bigger group
When awake-> diurnal than bigger group
Reproductive success of FEMALE depends on NUTRITION
Reproductive success of MALE depends on access to females
Alliances and Cooperation
Help a relative - share genes
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Most primates: females stay put and males move
-females form alliances with kin
Great Apes - females move, but still form bonds
Lots of variation in types of groups
Close kin avoid mating
MALE MATING STRATEGIES
Sexual selection
Male reproductive success - variable
TWO KINDS OF SEXUAL SELECTION:
I) Male competition - INTRA SEX SELECTION
II) Female choice - INTER SEX XELECTION
INTRA SEX:
A) males try to drive other males away
B) sperm quantity
INTER SEX:
Females are looking for: traits
A) increase female fitness
B) good genes: increase offspring fitness
C) conspicuous traits - may be non adaptive, but get males noticed
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VARIATION IN GROUP COMPOSITION
in some monogamous species: males care for offspring
in one-male/multi-female groups:
males compete to defend groups of females from other males
new males often commit infanticide to increase reproductive success
in multi-male/multi-female groups:
males compete within groups over access to females
dominant males have higher reproductive success
WRAP UP
Competition for food, resources, mating
BUT - even though is competition
PRIMATES interact peacefully, develop close bonds, cooperate
LIFE for primates - generally one of peaceful cooperation among kin