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Testing hypothesis 2. Predict: If high T b harms pregnant females, then 35 o treatment should have lower survivorship lower growth in mass or length Predict: If high T b harms embryos, then 35 o treatment should have more abnormalities smaller size at birth (mass, SVL)

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Testing hypothesis 2

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Testing hypothesis 2 l.jpg

Testing hypothesis 2

  • Predict:If high Tb harms pregnant females, then 35o treatment should have

    • lower survivorship

    • lower growth in mass or length

  • Predict:If high Tb harms embryos, then 35o treatment should have

    • more abnormalities

    • smaller size at birth (mass, SVL)

    • smaller sizes at 9 days


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Results: Effects on females

  • None

  • Survival = 100% for all

  • Growth not significantly altered by treatment

  • High temperature has no effect on females performance


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Results: Abnormalities

  • Of 15 females in each treatment:

    • at 35oC … 4 females produced 1 or more abnormal or dead offspring

    • at 32oC … 1 female produced 1 or more abnormal or dead offspring

    • in Treg … no females produced abnormal or dead offspring

  • abnormalities rather rare, hard to say much


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Results: Effects on embryos


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Conclusions

  • High temperature actually increases development rate of embryos

  • However, high temperatures reduce mass and SVL at birth

  • Effects of high temperatures remain for up to 9 days after birth

  • This size effect is probably sufficient to affect offspring fitness (survival)


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Overall conclusions

  • Pregant females actively regulate at a lower Tb because of negative effects of high temperature on offspring fitness

  • How might this evolve?

    • Quantitative trait: Tb when pregnant

    • Fitness differential (S): females with Tb = 32OC


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Physiological EcologySummary

  • Ecology of individuals

  • Adaptive value of physiological traits

  • Homeostasis (e.g., thermoregulation)

  • “How” vs. “Why” questions

  • Costs and constraints (e.g., S. merriami)

  • Benefits related to fitness (e.g., S. jarrovi)


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Behavioral Ecology

  • Another aspect of the ecology of individuals

  • The relationship between the living and nonliving environment and the actions of animals


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Topics within behavioral ecology

  • Foraging - how environment influences choice of what, how, when, where to eat

  • Social systems - how environment influences how individuals interact with conspecifics; living in groups

  • Sex and mating systems - environmental determinants of mating and reproduction


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Behavioral ecology focuses on adaptation and evolution

  • Main focus is on the adaptive value of observed traits in a given environment

  • There can be questions of both how and why concerning behavior

  • In both cases, approach is similar to that seen in physiologial ecology (costs, benefits, constraints)


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Living in groups

  • Many animals live in groups with conspecifics

    • Birds form feeding flocks, migrating flocks

    • Herds of herbivorous mammals

    • Schools of fish

    • Insect aggregations (e.g., monarch butterflies)

  • What determines group size?

  • What are benefits and costs?


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Major benefits of group living

  • Improved foraging success

  • Improved defense against enemies

  • Improved ability to cope with the physical environment


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End 9th Lecture


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Improved foraging success of groups

  • Improved location of food

  • Individuals observe one another and improve their chances by watching others succeed

  • e.g., blue herons - prefer to forage in areas where other herons are already foraging

  • species feeding on large ephemeral clumps of resources (e.g., fish)


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Improved foraging success of groups

  • Improved probability of capture

  • mammals - most predators fail more often than they succeed

  • lions

    • success rate double for 2 lions vs. 1 lion


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Improved foraging success of groups

  • Ability to take larger prey

  • group hunters - lion, spotted hyena, wolves, wild dog, kill prey >= their own mass

  • solitary hunters - leopard, coyote, striped hyena, kill prey < their own mass


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Improved defense against enemies in groups

  • Improved detection of predators

  • More eyes, noses, ears

  • greater probability of detecting predator

  • Bird flocks -- large flocks take flight when hawks are farther away

  • Advantage does not increase with group size indefinitely


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Improved defense against enemies in groups

  • Improved ability to deter a predator

  • Groups attack predator (e.g., gulls)

  • Chemical deterrence (e.g., pine sawflies)

  • Warning coloration - bigger signal


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Improved defense against enemies in groups

  • Confusing a predator

  • Many targets in a group -- hard to hit one

  • Shoals of fish attacked by squid

  • success rate of squid

    • single fish > small shoal > large shoal


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Improved defense against enemies in groups

  • Dilution effect

  • One predator takes one victim

  •  group size,  individual’s prob.(death)

  • Have conspecifics nearby so they can be the victim

  • Effect reduced if :

    • >1 individual taken

    • prob.(attack) increases with group size


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Forming selfish herds

  • Group = cooperation?

  • Animals may move to position conspecifics between themselves and predators

  • If predators take nearest animal, moving to center benefits individual

  • Result: form tight groups because each individual selfishly seeks middle


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Forming a selfish herd


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Forming a selfish herd


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Forming a selfish herd


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Forming a selfish herd


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Forming a selfish herd


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Forming a selfish herd


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Forming a selfish herd


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Forming a selfish herd

  • Point: Forming groups does NOT imply cooperation

  • Each individual may be acting selfishly for its own benefit

  • Effects on the group as a whole secondary


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Improved ability to cope with the physical environment in groups

  • Improved ability to thermoregulate

  • e.g., musk ox, roosting bats

    • groups minimize cost of thermoregulation by clustering

    • clustering reduces heat loss


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Benefits of group living weighed against costs

  • Aggressive interactions between conspecifics

  • Sharing resources that may be scarce

  • Nonexclusive access to mates

  • Disease transmission


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End 10thLecture


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Mating systems

  • Who mates with whom

  • Environment influences the mating system


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Sexual Selection

  • Selection that arises when individuals of one sex (usually ) gain advantages over other members of that sex in acquiring mates.

  • Darwin originated the concept

  • Now viewed as a subclass of natural selection


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Two kinds of sexual selection

  • Intrasexual selection: typically - competition

  •  compete for access to 

  • Darwin “power to conquer males in battle…”

  • Weapons; large, strong, aggressive 


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Characters for combat


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Two kinds of sexual selection

  • Intersexual selection: typically  choice of mates

  •  prefer  with particular characters

  • Darwin “power to charm females…”

  • showy structures, behaviors


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Characters to charm 


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Mating systems

  • Description of who mates with whom?

  • Differential investment of  and 

  •  - high cost gametes

    • produce few gametes

    • choosy

    • low variation in reproductive success

  •  - many, low cost gametes

    • produce many gametes

    • indiscriminant

    • high variation in reproductive success


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Mating systems

  • Promiscuous

    • all individuals mate with a number of mates

    • marine invertebrates, many insects, some fish, nearly all plants

  • Polygynous

    •  mate with >1;  mate with 1 at a time

    • many mammals, some birds, many insects, many amphibians


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Mating systems

  • Polyandrous

    • mate with >1;  mate with 1 at a time

    • a few birds, a few insects, a few fish

  • Monogamy

    • 1 with 1

    • many birds, some mammals, a few insects, some fish


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Mating systems depend on ecological conditions

  • Territories for mating, breeding (e.g., birds)

  • Resources (e.g., food, nest sites)

  • Defense against enemies

  •  gets material benefits from choosing certain 


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Mating systems depend on ecological conditions

  • Resources uniformly spread

    •  gain most by seeking unmated 

    • no sharing resources

    • Monogamy

  • Resources patchy (best males--best patches)

    •  may gain most by seeking best  (best patch) even if he has a mate

    • Polygyny


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End 11thLecture


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monogamous

2nd 

FEMALE FITNESS

5

4

3

2

1

Males

TERRITORY QUALITY

Polygyny threshold


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Ecology and mate choice

  • Distribution of resources influences mate choice

    • all territories good, resources uniform - monogamy

    • territories vary a lot in resources - polygyny


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Ecology and mate choice

  • What about cases where there is no material benefit?

  • Why should females prefer showy males?

  • Male quality

    • colors, ornaments, songs, displays etc. are costly

    • “good” males can pay that cost

    • handicap principle

    • Presumes “quality” is heritable


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Parasite-mediated sexual selection (Hamilton-Zuk Hypothesis)

  • Why should females prefer showy males?

  • Enemies (specifically parasites)

    • parasitized males have reduced showiness

    • showy colors  males resistant to local parasites

    • resistance to parasites heritable

    • benefit of choosing those males  resistant offspring

  • ectoparasites of birds - gnaw feathers

  • endoparasites - general reduction in vigor


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