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 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. 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? Reproduction effort may vary with latitude Duck and blackbird 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 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: 1.Chicks in larger broods would be survive poorly 2.At temperate and arctic latitudes, birds have longer days to gather food during summer when they reproduce young. 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. 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 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? 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. 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. Environmental conditions influence the evolution of life history traits Idea was conceived by Robert MacArthur and Edward O. Wilson: “rvs. K-selected strategists” Derivation of the terminology comes from population models (see future lecture): • “r” is population growth rate; rselected 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 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. 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 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. 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. 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 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. 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. Trade-off between fecundity and survival Relationship of adult’s fitness and fecundit F = S + S0 B S=SNSR F = S N SR + S 0 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 Survival rate and fecundity Different adult fitness High F, high survival of reproductive risk Large slope: high S0 and low Sn (high offspring survive and low adult survive) The trade-off between growth and fecundity Indeterminate growth: fish, reptiles, amphibians Different investments on growth and reproduction 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. 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. 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. Agaves and Lobelia telekii are semelparous plants Other semelparous examples Sockeye 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. periodical cicadas 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) 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 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 Desert annuals Extreme with released eggs of some fish such as cod (millions of eggs) etc 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. 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. 7.6 Life histories respond to variations in the environment Storage of food and buildup of reserves Dormancy Stimuli for change 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. 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 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 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) 7.7 Individual life histories are sensitive to environmental influences 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 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. 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. 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? 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. Optimal foraging model can be used to predict behavior Using a controlled experiment, Alex Kacelnik of Oxford University, tested how food load change with travel times Changed food availability and distance Risk-sensitive foraging Foraging is potential dangerous: risk factor James Gilliam and Douglas Fraser’s fish experiment The End Global warming and flowering time Started flowering observation study in Concord, Massachusetts 1852-1858: 500 plant species, weekly Alfred Hosmer: 1878, 1888-1902, 700 plant species Pennie Logemann: 1863-1993, 250 species Richard Primack and Arbaham MillerRushing (Boston University) 2003-2006, 43 common species Penology network: http://www.usanpn.org/ Henry David Thoreau (1817-1862) Mean annual T increased by 2.4 oC from 1852 to 2006 Flowering time of some species did not change, on average, flowering time today is 7 days earlier than 150 years ago Blueberry is 3-4 weeks earlier 8.1 Sexual or Asexual Reproduction Asexual reproduction (produce offspring without involving of egg and sperm) • • • • • • New individuals are the same as the parent Many plants (underground stem) such as strawberry; some animals (hydra, some aphids, parthenogenesis) If fitness is high, matches organism to environment If fitness is low, possible extinction (less variation) Stress can result in use of sexual cycle to give new gene combinations (hydra, aphid) Sexual Reproduction • More common form. • Can produce new gene combinations able to cope with a changing environment. • Greater energy commitment Specific organelles Production of gametes, courtship activities, and mating are energetically expensive. Feeding offspring The expense of reproduction is not shared equally by both sexes 8.2 Types of sexual reproduction Dioecious • Sexes are separate individuals • Greatest diversity of offspring Hermaphroditic • Perfect Male and females organs in same flower Can result in significant inbreeding • Monoecious Floral structure Plants Separate male and female flowers Reduces but does not eliminate inbreeding 8.3 Mating Systems describe pairing of males and females Different mating strategies have different advantages and disadvantages • Monogamy (one to one, form of a lasting pair bond between one male and one female) Most prevalent among birds, rare among mammals Seasonal or permanent • Allows sharing of cost of raising offspring • Increases survival chances of offspring • Cheating does occur and has specific advantages to fitness • Polygamy (one to two or more, a pair bond exists between individual and each mate) More than one mate of one sex for a single individual of the other sex (polygyny and polyandry) • Free individual to compete for resources and protect territory • Better food etc for mates • Some protection of offspring from competition • Promiscuity (one to one or many and no pair bound formed) Greatest number of offspring Large amount of competition Female only responsible for offspring in terms of resources • Poorer survival chance for offspring 8.4 Sexual Selection For Monogamy, Polygamy and Promiscuity • All involve the selection of a mate and therefore sexual selection • Selection for secondary sexual characteristics Peacock versus Peahen • Large tail feathers, more mating • Smaller tail feathers, less mating Deer • Characters that aid competition such as horns Humans • Faster sports car such as a Ferrari The End No only clutch size, the incubation time also varies Set nest boxes at two places Illinois Panama Monitor and collect newly laid eggs over one breeding season Eggs are marked by date and weighted Hatched in incubators at 37.8~38oC, RH 85-90% Another interesting thing is that it takes the same amount of time to hatch in nature and incubators (for current setting)
