BIOL 4120: Principles of Ecology Lecture 7: Life Histories and Evolutionary Fitness

1. BIOL 4120: Principles of Ecology Lecture 7: Life Histories and Evolutionary Fitness Dafeng Hui Office: Harned Hall 320 Phone: 963-5777 Email: dhui@tnstate.edu Http://faculty.tnstate.edu/dhui/biol4120

2. Life History Life history is species lifetime pattern of growth, development and reproduction. Measure of organism’s reproductive success is fitness: Those individuals who leave the largest number of mature offspring are the most fit the environments. Trade-off between growth and reproduction: mode of reproduction, age at rep., allocation to rep. number and size of eggs, young or seeds, parental care.

3. Reproduction efforts vary with latitude Why same species of birds, for example, songbirds in tropics, lay fewer eggs at a time than their counterparts that breed at high latitudes?

4. Reproduction effort may vary with latitude • Birds in temperate regions have a larger clutch size than tropical birds • Food supply, with longer day length in springtime to forage for food to support larger broods • large climate variation, decreases popul. below carrying capacity, need more young • Greater mortality in winter results in more food for survivors next spring Duck and blackbird

5. David Lack, Oxford University • 1947 • Birds would increase fitness by increasing clutch size, unless reduced survival of offspring in large broods offset this advantage • Hypotheses: • Chicks in larger broods would be survive poorly • At temperate and arctic latitudes, birds have longer days to gather food during summer when they reproduce young.

6. Experiments that adding eggs decrease survival of offspring Hogstedit, Science 1980: European magpie: Average clutch is 7 (maximum the pair can handle), add more or reduce could reduce the fitness.

7. Life History and Evolutionary Fitness 7.1 Trade-offs in the allocation of resources provide a basis for understanding life histories 7.2 Life histories vary along a slow-fast continuum 7.3 Life histories balance trade-offs between current and future reproduction 7.4 Semelparous organisms breed once and then die 7.5 Senescence is a decline in physiological function with increasing age 7.6 Life histories respond to variations in the environment 7.7 Individual life histories are sensitive to environmental influences 7.8 Animals forage in a manner that maximizes their fitness

8. 7.1 Trade-offs in the allocation of resources provide a basis for understanding life histories There are many trade-offs involved in reproduction effort decision Allocation of resources: Given time and resources are limited, how can the organisms best use them to achieve its maximum possible fitness?

9. Important stage of life history:Maturity, Age of first reproduction; Parity, number of episodes of reproduction; Fecundity, number of offspring produced per reproductive episode; Longevity, age to live.

10. 7.2 Life histories vary along a slow-fast continuum Life history traits of different species vary consistently with respect to environments; variation in one life history traits is often correlated to others. Variations can be arranged along a single continuum of values.

11. Environmental conditions influence the evolution of life history traits • Idea was conceived by Robert MacArthur and Edward O. Wilson: “r- vs. K-selected strategists” • Derivation of the terminology comes from population models (see future lecture): • “r” is population growth rate; r-selected species have traits that increase r • “K” is population carrying capacity; K-selected species have traits that increase carrying capacity and competitive ability when populations fill environment Spotted and redback salamanders

12. Examples of r- and K-selected organisms • r-selected organisms—short-lived, e.g., dandelion, with rapid population growth rate, small body size, early maturity, larger number of offspring, minimal parental care (animals). Inhabit unstable conditions, disturbed areas. • K-selected organisms –competitive species, long-lived, e.g., oak tree with long life, production of few, large seeds that can grow readily in shaded environments, but lack of mean of wide dispersal, poor colonizers of new or empty habitats.

13. 7.3 Life histories balance trade-offs between current and future reproduction Age at first reproduction Trade-off between fecundity and survival Trade-off between growth and fecundity

14. Important stage of life history:Maturity, Age of first reproduction; Parity, number of episodes of reproduction; Fecundity, number of offspring produced per reproductive episode; Longevity, age to live.

15. Age at first reproduction Long-lived organisms typically begin to reproduce at an older age than short-lived ones. Albatrosses (sea bird): high annual survival rate (94%), start at 10 yrs. Small songbirds: 50% survival rate, start at 1 yr. Natural selection favors the age of maturity that results in the greatest number of offspring over the lifetime of the individual.

16. Recap Acclimation and Developmental response Life history Life histories vary along a slow-fast continuum Grime’s plants: Competitors, Ruderal, and Stress Tolerators r- and k-selected strategists Life histories balance trade-offs between current and future reproduction Age at first production

17. Age at first reproduction Long-lived organisms typically begin to reproduce at an older age than short-lived ones. Albatrosses (sea bird): high annual survival rate (94%), start at 10 yrs. Small songbirds: 50% survival rate, start at 1 yr. Natural selection favors the age of maturity that results in the greatest number of offspring over the lifetime of the individual.

18. Trade-off between fecundity and survival Trade-off Experimental study to demonstrate that chicks with more competing siblings grow more slowly and fewer survive to reach adulthood. European kestrels Dijkstra et al. 1990.

19. Trade-off between fecundity and survival

20. Relationship of adult’s fitness and fecundity F = S + S0 B S=SNSR F = SNSR + S0 B SR = F/SN – (S0/SN) B F: adult’s fitness S: survival probability; SR: adult survival related to reproduction; SN: not directly related to reproduction; S0: survival to one year of age offspring B: # of offspring produced

21. Survival rate and fecundity Different adult fitness High F, high survival of reproductive risk

22. Large slope: high S0 and low Sn (high offspring survive and low adult survive)

23. The trade-off between growth and fecundity Indeterminate growth: fish, reptiles, amphibians Different investments on growth and reproduction

24. Animals: Ectothermic (cold-blooded) animals Production of offspring in fish increases with size, which increases with age Gizzard shad: 2-yr, 59,000 eggs 3-yr, 379,000 eggs Endothermic (warm-blooded): similar patterns exist for some animals European red squirrel: body weight and reproduction success; <300 g, do not reproduce.

25. Mortality rate influences life history Experiment of David Reznick et al. , UC Riverside, on guppy Poecilia reticulata Streams in Trinidad: waterfalls created two environments: below waterfalls, predators fish species (pike cichild and killifish); above waterfalls, relatively predator-free. Predators transplant experiment confirmed that after a few generations of adding predators, they showed same life histories.

26. 7.4 Semelparous organisms breed once and then die • Semelparity • One reproductive effort with all resources, then die • Most insects and other invertebrates, some fish (salmon) and many plants (bamboo, ragweed) • Some are small, short lived, grown in disturbed habitats; • Environmental effect can be disastrous • Iteroparity • Produce fewer young at one time and repeat reproduction throughout their lifetime • Multiple cycles of reproduction means the organism must balance growth, maintenance, escaping predators, defending territory, etc against reproduction • Most vertebrates, perennial herbaceous plants, shrubs, and trees. • Timing production: When – early or late • How many offspring: cost of the fecundity and its own survival.

27. Agaves and Lobelia telekii are semelparous plants

29. Other semelparous examplesSockeye salmon swim as far as 6,000 km from Pacific Ocean feeding grounds to spawning streams, lay thousands of eggs, then die from the exertion.

30. periodical cicadas

31. Parental investment depends on the number and size of offspring • Given certain resource allocated to rep., one can produce many small young or few large ones. The number of offspring affects parental investment. • Produce large number of offspring, less or no parental care (fish-eggs, plants-seeds) • Produce helpless offspring (produce young, spend less energy in incubation, but require considerable parental care) • Altricial • Mice • Longer period suckling • Robin • Other bird feeds • Produce more mature offspring (longer gestation, born in advantaged stage of development) • Precocial • Chicken, cow, deer, turkey Humans ? • Family care (Grandmothers, Grandfathers, Aunts, Uncles, Brothers and Sisters)

32. African elephants produce one offspring at a time, once every few years over a long lifetime, and protect each offspring intensively (much like humans) Few Number • More resources per individual • More chance of accidental loss

33. By contrast, many plants and some insects, reproduce once (annually), producing vast numbers of seeds/eggs that are poorly protected, if at all • Large Number • Less resources per individual • More chances of success • Extreme with released eggs of some fish such as cod (millions of eggs) etc Desert annuals

34. 7.5 Senescence is a decline in physiological function with increasing age Senescence: A gradual increase in mortality and a decline in fecundity as physiological function deteriorates over time. It’s a fact of life. Caused by natural wear and tear. Environments also influence, but mostly, it is under genetic control.

36. The strength of selection varies with extrinsic mortality rates The strength of selection for changes in mortality and fecundity at a particular age is related to the proportion of individuals in the population alive at that age, which depends largely on rates of mortality caused by extrinsic factors earlier in life.

37. 7.6 Life histories respond to variations in the environment Storage of food and buildup of reserves Dormancy Stimuli for change

38. Storage for food and buildup of reserves Plants and animals can store food and build reserves during the good environments. For example, Desert Cacti to store water; plants store nutrients; Arctic animals accumulate fat during mild weather in winter; winter active mammals (squirrels) and birds (acorn woodpeckers) cache food supplies. Chaparral plants store food reserves in fire-resistant root crowns.

39. Dormancy • Dormancy: physiologically inactive state. • Tropical and subtropical trees shed leaves during drought • Temperate and Arctic trees shed leaves in fall • Hibernate • Mammals: squirrels, bears? • Diapause: some insects entering resting state

40. Recap Life histories balance trade-offs between current and future reproduction Age at first production Survival and fecundity Growth and fecundity Parity and parental investment Senescence Life histories respond to variations in the environment Storage of resources Dormancy Stimuli for change

41. Stimuli for change Many events in life history of an organism are timed to match predictable change in environments. Proximate factors: day length etc, no direct effect on fitness; Ultimate factors: such as food supplies • Photoperiod: length of daytime • Different populations of a single species may differ greatly in their responses to photoperiod. • Side oats gama grass: southern, flower in winter (>13 hours); northern, flower in summer (>16 hrs) • Water fleas: Michgan, enter diapause in mid-Sept (<=12 hrs); Alaska, diapause in mid-August (<=20 hrs)

42. 7.7 Individual life histories are sensitive to environmental influences

43. Relationship between age and size at metamorphosis between frogs raised with high and low food suplies. Travis 1984. Marbled salamanders and spotted salamanders Gape-limited predation

44. The probability of survive from fire increases with increasing stem diameter. When fires are frequent, there is a strong selection of the rapid growth of stem at the expense of developing root systems.

45. 7.8 Animals forage in a manner that maximizes their fitness Foraging involves many different decisions to make, such as where to forage, how long to feed in a certain patch of habitat, which type of food to eat etc. Food supplies vary spatially, temporally, and with respect to the quality of food items; Foraging is dangerous as it expose the individual to predation. Optimal foraging: try to explain these behavioral responses in terms of the likely costs and benefits of each possible alternative behavior.

46. Central place foraging • When birds feed offspring in a nest, the chicks are tied to a single location, while the parents are free to search for food at some distance from the nest. This situation is referred to as Central Place Foraging. • Trade-offs: • Increase foraging distance, increase food availability, also increase the time, energy and risk costs of foraging • Is there some best distance from the nest at which a parent bird should forage, and how much food should the parent bring to its brood with each trip? How much time should the parent gathering food before it returns to its nest?

47. European starlings: • Forage on lawns or pasture for leatherjackets: capture time increases with number of prey already caught, maximum 8 can carries • Foraging trip including both the time spent at the foraging area and traveling time between foraging area and nest • Rate at which a parent can delivers food to its offspring is the number of prey caught divided by the time of foraging trips • How to maximum the rate? an individual can spend an intermediate amount of time at the foraging area during each trip and bring back something less than the maximum possible food load.

48. Optimal foraging model can be used to predict behavior

49. Using a controlled experiment, Alex Kacelnik of Oxford University, tested how food load change with travel times Changed food availability and distance

50. Risk-sensitive foraging Foraging is potential dangerous: risk factor James Gilliam and Douglas Fraser’s fish experiment