Ecology: the study of the relationship between animals and their environment
Behaviorual ecology: animal behaviors and their environment
Socioecology: relationship of an animal’s social behaviour and their environment
Ecological niche: aspects of an animal’s environment that are critical to than animal’s survival mating opportunities, food source, etc.
Look at socially close species and their behavioural patterns, and then differences in the aspects of the environment that pertain to survival. Then they look at ecological niche.
Socioecology Largest study was Weaver Birds they are a type of finches. They are composed of 90 subspecies. Great diverse behaviour patterns within these subspecies
– Crook: did the bulk of studies in socioecology. Studied mating strategies and other social behaviour.
Group behaviour of Weaver birds: tend to be solitary. Spend life alone or with mate, and others travel in large flocks (gregarious flock). Solitary vs. gregarious
Mating patterns: some species are monogamous (stay with the same mate for a whole season), and some stay with them longer. Some are polygamous (one male, multiple females).
Parenting: some Weaver birds share parental responsibilities (guarding the nest, feeding the babies), and in others, solely the female remains behind to take care of the babies. Monogamous ones are the ones that shared parental responsibilities.
Sex differences: sexual dimorphism differences between sexes in the species other than in terms of reproductive apparatus. Differences in size, plumage etc. Males are more aggressive than females.
The critical ecological variables underlying these differences were 2:
- Food source: what the animal eats
- Predation: what wants to eat the animal
Analyzed how these ecological differences determined behaviour.
- The most direct effect is on group behaviour. Where the animal lived (solitary or flocks)
- Effect depends mainly on whether the food source is dispersed or patchy
Species in the forest lived mainly on insects they are a dispersed food source (scattered evenly around the terrain). It is more adaptive for the animal to forage ALONE. Weaver birds in the forest divide the habitat into territories that are occupied by a single bird or pair.
- Birds who lived this way were fitter than birds who did not.
Birds who traveled in groups would not survive in the food source that is dispersed find a food source, and can only feed one or 2 birds.
Weaver birds in open plains (savanna) feed on grain, and grain is a patchy food source spread wider, and is in abundant quantities when it is found. Increased likelihood of finding food if the group searches together than solitary.
Predation
- Part of group selection
[Hamilton]: proposed an alternative called the geometry of the selfish herd – began his paper with a drawing of a circle saying it is a pond where frogs come to feed.
They are open to predation if they are around a pond
Squeeze yourself between 4 frogs, and it will be more difficult to get picked out when you are surrounded by other frogs
- Can explain large groups developing as a function of each individual’s selfish instinct to get between 2 other animals.
Problem: not the whole story. It breaks down in many species (the gazelle) – when they see a predator, they stomp to warn the rest of the herd, even if they are risking their own survival.
Mucks Oxen: form a circle, and the females and offspring go in the middle, and the predator moves away because it looks too dangerous.
Starlings: shadow of a predator bird appears, or any other sign of a predator – they close ranks. The flock flies widely apart, so they look like one big mass more difficult for the predator animal to grab one.
Parenting
The Weaver bird spends most of its time looking for food – and when they have offspring it takes up a lot of energy.
- The best adaption is monogamous and shared parental responsibility.
- Offspring would survive if it had 2 parents taking care of them, with shared energy and responsibility.
- Works best in forests when food is not as abundant – spend more energy looking for food.
For a weaverbird in a savannah is redundant, because there is plenty of food for every bird.
- The birds would be fitter if they were polygamous and wanting to mate with as many females as they can.
Females can bear a limited # of offspring, and you have: Male on male reproductive competition males compete for reproductive rights and mating privileges.
- Males compete for an actual resource like territory (the centremost position to build their own nests to get more attention from females)
- Competition is ‘ritualistic’: may have had function at a time, but now is more ritualistic. Ex. The Uganda Cope (?) – type of Reindeer. The sexes herd separately, and prior to the mating season, the males gather in a stamping ground (Buss calls it a Lek), and this is where males compete for mating privileges. The males fight for the centremost territory, don’t kill, but joust with horns.
- The females are in their herd, and then they wander in and pick mates while the males are sitting in their earned position
- The males go into a display when the females wander in their territory advertising his availability and readiness. If the female is not interested, he is gone back to grazing.
The females exercise choice, the female is the one who expresses willingness/permission.
Other reproductive patterns are harems: males have their own selection of females. Alpha Baboons have a harem.
The elephant seal: males come to shore, and battle for preferred areas closer to the females. The larger males win, and when the females come, they will keep them for themselves in a harem.
Bower Bird: build bowers (little shelter) with coloured rocks in their habitat, and try to build a nice shelter.
They sing in these shelters, and the females walk around these shelters looking for the best shelter/song.
- Competition without direct competition/conformation.
- Same with peacock: the biggest and largest display intimidates other male competitors and females like it.
Hypergamy: females mate upward in status, and males must compete with other males (symbolic as well) or by demonstrating capacity and strength. Females look at mates by their capacity to gain resources.
Polygyny: the fittest males will mate with multiple females, and there will be a supply of unwanted males at the bottom. Most are losers!
- In terms of evolutionary psychology, it is a statistical concept. Measured in terms of whether the males have more sexual partners than females. Within any pop’n they have the same # of mating episodes, but it is when the distributions are different (females is not as wide as male, do not have multiple mates).
- Variance of the males is wider.
Why is the reverse not the rule? (polyandry):
- Females are limited in procreative capacity, and males can father thousands whereas females are max. 15.
- Females have a larger investment reproductive strategy is based on more careful selection.
Sex differences
Weaver birds – Female selection in males for whatever trait relates to fitness. Males in reproduction competition will tend to get bigger sexual dimorphism in males vs. female in size and strength.
Males larger than females, and the plumage was more prominent.
The more male v. male competition, the greater the difference between the size of the sexes will occur. – Baboons and Elephant seals – females are a third of the size than males
– In monogamous species (birds, beavers, elephants) with less intense reproductive competition, you get less size difference/dimorphism.
Sexual dimorphism also occurs in the presence of horns, and behaviour – more aggressive, assertive male.
One problem: plumage in male birds (peacock, for ex) does not seem adaptive. It is maladaptive at first glance it attracts predators, and it is a heavy load for the animal to carry – They still prevail, and females enjoy this display.
Zahabi: has a theory to this. The handicap principle he is advertising is courage and strength both to females and other males. “I can carry this on by back and accomplish more/the same as you do”.
Silverman: risk-taking – human parallel to this. It is done from early childhood in little boys to life. Girls seem to like this
Review:
2 basic social structures – solitary vs. monogamous. Not much aggression in males, sexual dimorphism etc.
This stems from food sources and predation.
- This holds well across species, but there are some exceptions
Variations on these styles, but can be explained by variation in food sources. Live in couples when there is dispersed, and have large flocks in other parts of the year.
Another variation is when food supplies fluctuate depends on the whether – you get 2 personality types in the male. One that is monogamous, and the other which is competitive and polygamous. Different members of the pop’n passing on different patterns
- Seen in humans as well. “Dads and Chads”
The human case
- At one time, we were vegetarians (hominids) lived in the forest, and food was dispersed. We lived on vegetables, and were nomadic and monogamous.
- Food source became unpredictable, and we extended our diet to include meat (a patchy food source)
- Began to aggregate more into groups hunter/gatherer tribes, colonies etc.
- When we began living in groups, we may have become more polygamous. Diet change caused us to adapt to different lifestyles.
Today, most societies are polygynous, some more explicitly or implicitly. – Usually males that copulate outside the pair-bond.
Sexual dimorphism is in humans as well: competitiveness, aggressiveness etc.
Competition in female size females are bigger.