Week 11, Lecture 18 - Territoriality & Conflict

Territory

an area defended to obtain exclusive access to the resources it contains

Home range

Areas of repeated use that are not defended from conspecifics

territoriality and Yarrow’s spiny lizard

info: male lizards set up breeding territories which they defend!

methods: researchers implanted testosterone under skin for 1/2, other half they had “control” capsules

results: lizards with testosterone spent more time defending territories! also.. testo lizards did not survive as well as controls… due to testo or to energy??

experiment 2: group 1 = no testo, group 2 = testo but extra supplement, group 3 = control implant and no extra food —> measured survival of all 3!

supplement + testo survived most, testo plus no supplement survived least!

American Redstarts and territoriality payoff

• birds that controlled high quality territories gained weight faster in spring & were able to leave for summer breeding earlier!!

• territory matters for later life cycle things!

• payoff for leaving wintering grounds earlier… males can arrive earlier to establish breeding territories, females arrive earlier to select and have choice of best, both sexes = higher breeding success!

poplar aphids & habitat selection

• parthenogenetic (no males) + make homes in poplar leaves by making “gall” - little cocoon at basal stem part

• fitness increases for the aphids if they are the ONLY aphid on the leaf and in the best position (get more of the resources and don’t have to share!)

• so defending territory = beneficial

cost/benefit of maintaining a territory

• territory should decline with… increase in resource density! (no need to go bigger) orrrr in density of competitors (too risky to go bigger)

white-tailed kite territory size

• estimated abundance of food items (voles) and competitors (hawks)

• territory size declined with increasing density of voles (more prey = no need to defend large territory)

• territory size declined with increasing competitor abundance (more predators = scary to go bigger.. must avoid conflict!)

Resource Holding Potential (RHP)

• main factor of resource holding is the ability to defend a resource from others

• reflects these characteristics: size (bigger is better in a fight), health & energy (affects stamina)

important factors of contests for resources

motivation to fight due to…

• hormones

• value of resource

• relative value of the resource

RHP in damselflies

info: male damselflies feed for several days and then seek to establish a territory! some males succeed and others do not

• no correlation between size but.. males win by chasing away other males - bothering the intruders… this is HIGH ENERGY ACTIVITY!

males who succeeded in getting a territory had higher fat reserves than nonterritorial males

• tested if fat reserves are used up in defense of territory - introduced intruder - fat reserves were used up!!!

fat reserves clearly needed for defense of territory - RHP in this case depends on fat reserves!

sequential assessment RHP in fiddler crabs

• sequential assessment = to analyze or to determine how far to proceed with flight to start with low cost actions and move to high cost actions

• fiddler crabs do this - start with low cost, move to high cost as they measure opponents strengths!

california mouse and the challenge & winner effects

methods: males were exposed to trainings where they win 0, 1, 2, or 3 encounters with other male mice

results: winning the previous encounters increased testosterone levels (the challenge effect)

• added new larger male…. males that had won more fights were now quicker to attack, and more likely to win!! (winner effect)

is winner effect a result of testosterone from challenge effect?

methods: some mice were trained as winners and given extra testo, some just given testo, controls no testo

results: extra testo increased likelihood of winning, even when the mouse was not already a winner!!

• testo may have increased aggression… as recipients attacked more quickly than controls

bystander effect

idea that observing a fight can raise testosterone levels

bystander effect in fish!

• treatment: male bystander viewed an aggressive interaction through one way glass, control male did not; measured testo at start and after 30 mins

• bystanders had higher levels than controls!!! controls went down…

bystander effect in hockey players

hockey players shown videos of their team winning or losing, or neutral.. testo went up if they saw the winning one!

red-spotted newts and value of resource

info: newts fight for access to females by “wrestling” - winner is the one that is bigger, but if equal size, then winner is the one that lasts longest

methods: researchers staged encounters b/w size matched males, varied size of female to communicate “value” of female

• duration of wrestling is positively correlated with female body length! conclusion = the more valuable the resource the harder the newts fight!

asymmetry of value of resource in frontinella spider!

info: females have 40 eggs and during breeding season 1 in 4 females have eggs

• as the number of eggs increase, the value to the resident increases!!! but the intruder it stays the same? also throughout preinsemination increases, but post insemination decreases…

• number of contests won of residents will decrease as copulation continues,