Ecology of individuals

 

  1. General considerations
    1. Hierarchy of organization
      1. All biology organized into hierarchy
      2. Individual, population, community
    2. Definition of ecology: study of interrelationships of organisms and the environment
    3. Individual ecology
      1. habitat selection
      2. behavior
      3. partitioning of time
      4. partitioning of energy
      5. growth, survival and reproduction as affected by environmental factors
  2. Life history: Definition and general importance
    1. Key quantitative features of the life cycle
      1. Size at birth
      2. Age and size-specific pattern of growth
      3. Age, size at maturity
      4. Age and size-specific pattern of reproduction (including number, size, sex ratio of offspring)
      5. Age and size-specific pattern of mortality
    2. Explaining diversity in life histories
      1. Organisms are quite variable in life history traits
        1. Among species
          1. Some flounders are adults at a couple inches, mature in first year
          2. Some species reach lengths of 2 meters, mature at 10 years
        2. Even within species, among populations
          1. Species of flatfish that matures in 3 years, 20 cm, in Scotland, takes 15 years, 40 cm, off Newfoundland
      2. Part of task: understanding relationships among life history traits
  3. Tradeoff: the cost of reproduction
    1. Tradeoffs: linkages between traits that constrain their simultaneous evolution.
      1. Can't maximize everything: rapid growth, large reproductive output, high survival.
    2. A number of tradeoffs are referred to as 'costs of reproduction'
      1. Refers specifically to the tradeoff between present and future reproduction
    3. Three basic kinds of reproductive costs
      1. Fecundity cost

        2. Energy allocated to reproduction now comes at the expense of fecundity in some future reproductive bout

      2. Growth costs (special case of fecundity costs)

        3. Energy that is allocated to reproduction comes at the expense of growth. Note that growth increases future reproduction.

      3. Survival costs

        4. Energy that is allocated to reproduction comes at the expense of survival probability, which reduces future reproductive prospects.

      4. Growth cost:
        1. Warner: IP males with low opportunity for breeding grew faster
        2. But Reznick found no enhancement of growth in length, only higher fat storage
  4. Characteristics of reproductive strategies
    1. when to spawn in lifetime
      1. age/size of maturation
        1. some mature at birth, short life (dwarf surfperch)
        2. some don't mature for decades (spiny dogfish, sturgeon)
        3. Environmental effects, variation within population: fast growth means earlier maturation
        4. selection on earlier maturation: one factor is high predation on adults. Reznick guppies: in high predation envts., females and males mature at 15 mm, in low predation envts at 18.
      2. semelparity vs iteroparity
        1. most iteroparous
        2. some exclusively semelparous: eg some Oncorhynchus
        3. variation within species: American shad, southern spp entirely semel, whereas northern pops half of indivs or more survive and reproduce again. (figure 16.3, p 326 Diana)
    2. reproductive investment
      1. reproductive effort
        1. proportion of available energy devoted to reproduction
        2. if RE=1, semelparous
        3. energy to produce eggs and sperm, get mates, raise offspring
        4. conceptually important but can be difficult to quantify
      2. reproductive allocation: one proxy
        1. GSI; variation among species (p. 135 Roff)
        2. selection: Reznick nature paper. RA is higher in a high-predation envt.
      3. fecundity
        1. variation among fishes (fig 8.4, p. 173 Bone)
        2. variation within species: (Fig. 16-5 Bond)
        3. increases with size, exponentially; generally to the third power of length.
        4. increases with environmental factors: e.g. higher food consumption
      4. egg size (investment per young)
        1. varies among species
        2. measure at moment of offspring independence, so investment in parental care can be included
        3. varies within species: bigger with more food, greater age, decreases over the season (fig 8.4, p. 173 Bone)
        4. expected consequences:
          1. larger offspring has more reserves, better competitive ability, better able to swim
          2. but if have larger offspring, must have fewer of them
      5. parental care: ca 20% of fish species care for young
        1. guarding nest is most common
          1. fanning eggs
          2. oral brooding
          3. eggs embedded in skin (some catfishes), brood pouches, weird hooks
          4. may vary within species: e.g. Symphodus: early in season, males and females scatter eggs in algae, but later males set up nests and guard eggs from snails and other fishes
        2. further nourishment
          1. after eggs hatch and yolk is used up, there are other means of feeding young
          2. live bearing fishes
            1. ovoviviparity (lecithotrophy): all nourishment provisioned in egg
            2. viviparity (matrotrophy): further nutrition

              3. offspring eating other eggs or siblings

              placental analogues: special secretions by female, and absorptive structures in offspring

            3. viviparity usually obligate
          3. some fish nourish young after birth:
            1. discus fish (cichlidae), mothers secrete milk from skin
            2. other cichlids help offspring get food by stirring up bottom
      6. parental investment: functions to produce larger, more competent offspring with relatively low mortality rates; trades off with offspring number.