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Chapter 60: Behavioral Ecology

Chapter Outline

Chapter 60: Behavioral Ecology

60.0 Introduction

  1. The Adaptiveness of Behavior
    1. The Function of Behavior Is Its Survival Value
    2. Behavior Allows Animal to Increase Its Reproductive Success fig 60.1
60.1 Evolutionary forces shape behavior

  1. Behavioral Ecology
    1. Behavior Has Survival Value
      1. Evolutionary analysis of how behavior helps an animal or its offspring stay alive
      2. Example: Tinbergen's gull egg shell experiments fig 60.2
        1. Gull parents remove hatched eggshells from nest
        2. If broken shells replaced, predation increased
        3. White shell interior cues predators
        4. Shell removal behavior is adaptive, increases survival of offspring
      3. Behavioral ecology is the study of how natural selection shapes behavior
      4. Adaptive significance of behavior
        1. How behavior increases survival and reproduction
        2. Recent studies examine animal's fitness or reproductive success
        3. How behavior is related to fitness = study of adaptation itself
      5. Natural selection acts on genetic component of behavioral differences
        1. Behavior favoring reproductive success becomes more prevalent fig 60.3
        2. Test hypothesis by measuring fitness, demonstrating its correlation with behavior
        3. May also measure other factors associated with reproduction
  2. Foraging Behavior
    1. Specialists versus Generalists
      1. Specialists feed on only one kind of food
        1. Example: Some ants eat only spider eggs
        2. Example: Oystercatchers feed on only mussels fig 60.4
      2. Generalists feed on many different kinds of food
        1. Example: Some insects eat leaves of a wide variety of plants
        2. Not as efficient as specialists at catching any one kind of food
        3. Take advantage of finding many different varieties
      3. Foraging trade-offs between food energy content and availablilty
        1. Large food contains more energy, harder to capture, less abundant
        2. Net energy = energy of prey - energy cost of pursuit and handling
      4. Optimal foraging theory
        1. Expect evolution to favor foraging efficiency
        2. Feed on prey that maximizes energy intake per unit foraging time fig 60.5
      5. Predictions made by optimal foraging theory
        1. Where animal will search for food
        2. How long animal stays in one area before moving to another
        3. Animals cannot always maximize energy intake
          1. Nutrition and variety of food must be considered
          2. Compromises made because of predation by others
    2. Predator-Prey Arms Race
      1. Predators evolve greater effectiveness in catching prey
      2. Prey evolve to better deter being preyed upon
        1. Prey defense mechanisms of camouflage, mimicry, active defense
        2. Often exploit behavior of predator
          1. Batesian mimics protected by convergent color
          2. Predator avoids attacking prey that resemble mimic's model
      3. Predators increase ability to detect cryptic prey through learning
        1. Blue jay trained through operant conditioning
          1. Finds image of cryptically colored moth in photographic slide
          2. Bird received reward for seeing moth
        2. Performance improved if one species of prey shown
        3. Unable to increase performance if two species shown in slides
          1. Specialist predators can learn to perceive cryptic prey
          2. Generalist predators unable to learn
60.2 Reproductive behavior involves many choices influenced by natural selection
  1. Territorial Behavior
    1. Animals Move Over a Large Area
      1. Home range: Daily activity site
        1. May overlap with others in time or space
        2. Portion of range is exclusive and actively defended
      2. Territoriality fig 60.6
        1. Individual exclusively uses area with some limited resource
        2. Resources may include food or potential mates
        3. Defense of area via displays or overt aggression
        4. Example; Bird song to defend territory
          1. Done to prevent takeover of territory by neighboring birds
          2. Intruders not deterred may be attacked
        5. Defense of territory has cost
          1. Singing is energetically expensive
          2. Attacks can lead to injury
          3. Advertisement by song or display may attract predators
      3. Economic risks of territorial behavior
        1. Energy costs versus energy benefits
        2. Example: Flowers and nectar-feeding birds fig 60.7
          1. Cost depends on amount of food available, efficiency of collection
          2. If flowers scarce, not worth defending since they do not provide enough energy
          3. If abundant, not worth defending, easy to get enough energy
          4. Defense practical for only for intermediate quantity of flowers
  2. The Ecology of Reproduction
    1. Decisions Made About Mate Choice During Breeding Season
      1. Reproductive strategy: Behaviors that maximize reproductive success
      2. Include mate choice, number of mates and parental care
      3. Evolved in response to ecology, food resources, nest sites, distribution of mates
      4. Mate choice first observed by Darwin fig 60.8
        1. Males and females differ in reproductive strategies
        2. Female's evaluate male's quality, decide whether or not to mate
        3. Superior mates should leave more offspring
        4. Measurement of mate quality
          1. Good genes passed to offspring
          2. Material gains like food resources or nesting sites
    2. Parental Investment and Mate Choice
      1. Question which sex should show mate choice
        1. Compare contributions of each parent to raising offspring
        2. Estimate energy spent by male and female in offspring care
      2. Parent with the greatest cost should make choice for mate
      3. Females generally show higher parental investment
        1. Size of gametes: Egg significantly larger than sperm
        2. Nutritional value of gametes: Egg more than sperm
        3. Care costly to females that gestate and lactate
      4. Males may show mate choice if they have high parental investment
        1. Example: Male cricket spermatophore = 30% of body weight
          1. Provides nutrition for female2) Helps develop eggs
        2. Females compete for males
        3. Males choose large females to produce more offspring fig 60.9
        4. Males make investment by defending and feeding young
  3. Reproductive Competition and Sexual Selection
    1. Reproductive Competition
      1. Competitive interactions over access to mates
        1. Females frequently choose largest male as mate
        2. May be associated with competition between other males
          1. Larger males win disputes over smaller, younger males
          2. Larger males more successful at defending territory used as nesting site
        3. Few males in population may sire most of offspring fig 60.10
      2. Competition does not always involve aggression
        1. Example: Elaborate feathers and vocalizations of male bird of paradise
        2. Females choose most impressive male
      3. Impressive feathers, vocalizations may pose survival problem for male fig 60.11
        1. Males become more conspicuous to predators
        2. Male survival therefore placed at risk
        3. Process not a natural selection process
      4. Sexual selection involved in evolution of male ornamentation
        1. Involves intrasexual selection, between individuals of same sex
        2. Involves intersexual selection, choice of mate
        3. Causes development of secondary sexual characteristics fig 60.12
      5. Exaggeration of trait could occur if mate showed preference for that trait
        1. Tail length in males increases as long as females choose it
        2. Choice of tail length stops when it decreases their survival
      6. Secondary sexual characteristics may reflect true quality
        1. May advertise superior genes
        2. Resistance to parasites reflected in bright coloration
        3. Symmetry greater in longer feathers, symmetry indicates ability to resist stress
      7. Evolution of courtship displays
        1. Female predisposition to be stimulated by certain signals
        2. Signals include color, vocalization, body ornaments
        3. Males evolve attractive signal by exploiting females response to signals
        4. Example: Frog vocalizations fig 60.11
          1. Males add notes to make signals more attractive to females
          2. Added notes not used by ancestral species
          3. Females still find added notes attractive
          4. Female sensory system reaction fostered evolution of notes by male
    2. The Benefits of Mate Choice
      1. Individual receives mate's good genes to promote survival and fitness of offspring
        1. Example: Fruit flies
          1. More progeny survive when female fruit flies choose mates
          2. Fewer survive when mates chosen at random
        2. Example: Spadefoot toads
          1. Females select large males for mates
          2. Sperm from large males produce tadpoles that mature more rapidly
          3. Tadpoles more likely to metamorphose before pond dries up
        3. Genes coding for survival passed from males to offspring
      2. Mate may provide resources needed for reproduction
        1. Territory male defends contain high quality resources
        2. May include nutritional materials or nesting sites
      3. Few excellent long-term studies of mating behavior and reproductive success
        1. Example: Red deer
          1. Size, age, territory defense ability, number of females critical to male reproductive success
          2. Female success determined by quality of feeding grasses, time of birth, longevity
  4. Mating Systems
    1. Species Variation in Number of Individuals Mated With
      1. Three primary mating systems
        1. Monogamy: One male to one female fig 60.13
        2. Polygamy: One male to more than one female fig 60.14
        3. Polyandry: One female to more than one male
      2. System evolves to maximize reproductive fitness, influenced by ecology
        1. Area with enough resources can support more than one female
        2. If quality of area varies, female is better off with already paired male in good area, than unpaired male in poor area
      3. Needs of young also constrain mating decisions
        1. Monogamy favored if both parents needed
        2. Altricial young need extensive care, both parents needed (monogamy)
        3. Precocial young require little care, decreasing need for males (polygamy)
      4. Timing of female reproduction also affects mating system
        1. All females receptive at same time, males unable to secure large number of mates
        2. May dictate whether males can take advantage of ecological opportunities
60.3 There is considerable controversy about the evolution of social behavior

  1. The Evolution of Animal Societies
    1. Most Animals Live in Social Groups
      1. Society: Cooperative group of individuals of same species
      2. Sociobiology: Biological basis of social behavior
        1. Study animal social behavior as biological process
        2. Has genetic basis shaped by evolution
        3. Predicts that behavioral characteristics are adaptive and suited to mode of living
    2. Group Living
      1. Is basically a selfish behavior
        1. Results in greater protection from predators fig 60.15
        2. Individual may acquire feeding information from others
      2. Disadvantages
        1. Parasites and disease spreads more readily
      3. Must balance disadvantages and advantages
        1. Example: Cliff swallows fig 60.16
          1. Large groups have increased feeding rates
          2. Greater number of young succumb to ectoparasites
    3. The Evolution of Altruism
      1. Altruism: Self-sacrificing behavior
        1. Important aspect of cooperation
        2. Involved with assisting other individuals in reproducing
      2. Group selection incorrectly used to explain regulation of population size
        1. Non-territorial, non-mating males don't reproduction to limit population size
        2. Good for species, as not to exhaust limited resources
        3. Flaw: Altruistic trait could not be passed to next generation since male with trait does not reproduce
    4. Reciprocity
      1. Partnership formed to exchange altruistic acts
      2. Reciprocal altruism: Altruists are mutually reciprocated
        1. Individuals of altruistic pair are unrelated
        2. Share no common genes
      3. Non-reciprocators are cut off from receiving future aid
        1. If altruistic act is inexpensive, gain to cheater is not worth future lack of reciprocation
        2. Example: Vampire bats fig 60.16
          1. Bats that have fed well give up small amount to roostmate
          2. Individual that does not reciprocate excluded from future sharing
    5. Kin Selection
      1. Haldane's remark to lay down his life for two brothers or eight first cousins
        1. Shares 50% of genes with brothers
        2. Passes on as many genes as eight first cousins, each shares 1/8 of his genes
      2. Hamilton's theory: Evolution favors strategy that increases net flow of a combination of genes to the
        next generation
      3. Costs and benefits of altruism
        1. Direct aid to kin = reduction in own fitness outweighed by increased reproductive success of relatives
        2. Selection favors behavior maximizing propagation of alleles
      4. Kin selection theory: Favor propagation of genes by directing altruism to relatives
        1. Inclusive fitness: Genes propagated by reproduction plus effect of help on reproducing by relatives
          1. Does not equal number of direct genes via own offspring plus genes from non-offspring relatives
          2. Fitness has both personal and kin-selected components
          3. Altruism is likely to be directed to close relatives
          4. Hamilton's rule: b/c > 1/r
            1. b = benefit of altruistic act
            2. c = cost of altruistic act
            3. r = coefficient of relatedness
  2. Insect Societies
    1. Organization of Eusocial Insect Societies
      1. Composition of a honeybee hive fig 60.17
        1. Single queen, sole egg-layer
        2. Up to 50,000 offspring of queen, mostly female workers with nonfunctional ovaries
          1. Sterility of workers is altruistic
          2. Offspring give up reproduction to help mother rear more sisters
      2. Sociality evolved in two insect orders
        1. Hymenoptera include ants, bees, wasps
        2. Isoptera includes termites
      3. Eusocial insects are truly social with division of labor
        1. Include all ants, some bees, some wasps, all termites
        2. Division of reproductive labor (fertile queen, sterile workers)
        3. Provide cooperative care of brood
        4. Have overlap of generations, queen lives alongside offspring
        5. Composed of castes, highly integrated groups of individuals
      4. Possess haplodiploidy system of sex determination
        1. Workers share as much as 75% of genes
        2. Males are haploid, females are diploid
        3. Altruism allows workers to maximize inclusive fitness
      5. Queen maintains dominance by "queen substance" pheromone
        1. Suppresses ovaries in female workers, makes them sterile workers
        2. Male drones produced only for mating
        3. With hive growth in spring, some females do not receive enough queen substance
          1. Colony prepares for swarming
          2. Workers establish several queen chambers
          3. Old queen and some females workers move to a new hive
          4. New queens battle, winner mates and rules old hive
  3. Natural History of Leaf Cutter Ants
    1. Colonies of millions of ants grow crops of fungi underground from leaf pieces
    2. Division of labor related to worker size fig 60.18
      1. Workers travel from nest to tree or bush, cut leaves into small pieces, carry to nest
      2. Smaller workers chew leaves into mulch
      3. Still smaller workers implant fungal hyphae into mulch
    3. Nurse workers carry larvae to choice spots in fungal garden to graze
    4. Queens produced that disperse from parent nest and start new colonies
    5. Few other invertebrates are eusocial
      1. Species of shrimp that lives in sponge
      2. Also some thrips and a species of weevil
      3. Support theory of cooperation proposed by kin selection
60.4 Vertebrates exhibit a broad range of social behaviors

  1. Vertebrate Societies
    1. Vertebrate Societies Are Less Rigidly Organized than Insect Societies
      1. Vertebrates have larger brains, more complex behavior
      2. Exhibit lower degree of altruism
      3. Apparently due to lower amount of shared genes
        1. Maximum shared 50%
        2. Social systems still show reciprocity and kin-selected altruism
        3. Exhibit greater degree of conflict and aggression within society
        4. Conflicts center around food resources and mates
    2. Altruism in Vertebrates
      1. Cooperative breeding systems in birds
        1. Example: Scrubjays
          1. Helpers at the nest assist one breeding pair
          2. Help feed offspring, watch for predators, defend territory
          3. Can reproduce but do not for a period of time
          4. Nest with helpers have more offspring tbl 60.1
          5. Helpers are often fledged offspring of those they help
          6. Resembles family situation
        2. Example: White-fronted bee-eaters
          1. Nests located on face of cliff
          2. Up to 25 families comprise single colony
          3. Helpers assist breeding pairs
          4. More likely to help when greater degree of relatedness
        3. Example: African kingfishers
          1. Helpers may be related or unrelated to assisted breeding pair
          2. Pursue different breeding strategies
        4. Evolution of cooperative breeding explained via inclusive fitness concept
      2. Vertebrate sociality
        1. Activity of certain individuals benefit group at expense to individual
          1. Individual exposed to predators, environment
          2. Draws attention to self, thus exposed to greater danger than non-sentries
          3. Behavior seems contrary to individual's self-interest
        2. Example: Meerkat alarm calling fig 60.3
          1. Individuals act as sentries for group
            1. May give alarm call when predator sighted
            2. Draws attention to itself to protect others
          2. Places self in jeopardy, reveals own location
        3. Example: Belding's ground squirrel alarm calling
          1. Alarm call given when predator sighted, caller at risk
          2. Colonies female-based, males not related to any females
          3. Females with relatives nearby more likely to sound alarm than females with no kin nearby
        4. Alarm calling represents nepotism, favors relatives
        5. Evolution of system explained by kin selection model
    3. Organization of Vertebrate Societies
      1. Vertebrate societies have characteristic organization fig 60.19
        1. Group has certain size, stability of members
        2. Characteristic number of breeding males and females
        3. Specific type of mating system
      2. Social organization of group influenced by ecological factors, food type and predation
      3. Example: African weaver birds
        1. Forest species
          1. Builds camouflaged solitary nest
          2. Monogamous mating
          3. Eat and feed young with insects
        2. Savanna species fig 60.20
          1. Nest in colonies in trees
          2. Polygynous mating
          3. Feed in flocks on seeds
        3. Feeding and nesting depend on area ecology
          1. Hiding nest not an option on open savanna
          2. Protection on savanna via colonial nesting in rare spiny trees
          3. Abundant seeds readily collected by single female, male's help not needed
          4. Males freed from parenting, compete with other males, breed more females
      4. Example: Naked mole rats
        1. Organized very much like insect societies
          1. Form large underground colonies, running tunnels, central nesting area
          2. May contain up to 80 individuals in one colony
          3. Feed on bulbs, roots, tubers found by constant tunneling
        2. Have functional division of labor
          1. Some work as tunnelers, others perform other tasks depending on body size
          2. Large individuals defend colony, dig tunnels
          3. Have reproductive division of labor like eusocial insects
            1. All breeding via single female with one or two male consorts
            2. Workers are of both sexes
            3. Colonies may share up to 80% of alleles, due to inbreeding
          4. Kin selection important in evolution of this society
  2. Human Sociobiology
    1. Theories of Animal Sociobiology and Human Applications
      1. Comparative aspects of sociobiology
        1. Theoretical concepts applied to behavior in different species
        2. Altruism in different species explained by kin selection
        3. Social behavior has biological basis
      2. Examine human activities in same light
        1. Social species with unparalleled complexity
        2. Only species with intelligence to contemplate social behavior of other species
        3. Exhibit kin-selected altruism, reciprocity, elaborate social contracts
        4. Show extensive parental care of offspring
        5. Have conflicts between parents and offspring, violence, warfare
        6. Possess variety of mating systems
      3. Exhibit unevolutionary behaviors like adoption
    2. Biological and Cultural Evolution
      1. Two processes led to adaptive change2. Biological evolution
        1. Primate heritage shared with chimpanzees
        2. Traits are definitely adaptive in non-human primates
        3. Include kin-selected and reciprocal altruism
        4. Similar traits likely evolved in early humans
          1. Advantage in reproduction conferred to individuals with these traits
          2. Traits now part of human genome, may influence behavior
        5. Cultural evolution
          1. Transfer of information needed for survival across generations
          2. Nongenetic mode of adaptation
            1. Includes use of tools, shelter construction, marriage practices
            2. Passed from generation to generation by tradition
    3. Identifying the Biological Components of Human Behavior
      1. Difficult to identify
        1. Study cross-cultural traits
        2. May have been affected by natural selection
        3. May result from genes fixed in human populations
        4. Examples:
          1. Most mammals and human species are polygamous
          2. Many cultures exhibit same greeting pattern
      2. Development of evolutionary psychology
        1. Understand origins of human mind
        2. Diversity of cultures developed from adaptations to ancestral hunter-gatherer lifestyle
        3. Human behavior reflects ancient, adaptive traits
        4. Even behaviors like jealousy and infidelity increased fitness of ancestors
        5. Traits now part of human psyche

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