Life History PDF

Life History 1 All organisms produce Family structure can offspring, but the vary significantly number and size of from human-like offspring vary families. greatly. 2 1 Introduction...

Life History 1 All organisms produce Family structure can offspring, but the vary significantly number and size of from human-like offspring vary families. greatly. 2 1 Introduction An organism’s life history is a record of events relating to its growth, development, reproduction, and survival.  Age and size at sexual maturity  Amount and timing of reproduction  Survival and mortality rates The life history strategy of a species is the overall pattern in average timing and nature of life history events. 3 Life History Characteristics Life history patterns vary within and among species. Life history strategy is determined by effects of natural selection, not the choices of the individual organism. 4 2 Life History Diversity Within a species, individuals differ in their life histories. Why? 1.Genetic difference Trait is heritable Allows for natural selection. Traits that maximize fitness persist Fitness = genetic contribution of an organism’s decedents to future generations (survival + finding a mate + reproducing). 5 Life History Diversity 2. Environmental Conditions - Phenotypic plasticity: One genotype may produce different phenotypes under different environmental conditions. E.g., Individuals changing appearance seasonally Wet season Dry season appearance: appearance: primary predator primary predator is praying mantis is birds 6 3 Acclimatization vs. Phenotypic Plasticity Acclimatization: an organism’s adjustment of its physiology, morphology, or behavior to lessen the effects of an environmental change and minimize associated stress Short-term, reversable Note: “Acclimation” is the same response in artificial/lab conditions 7 Acclimatization vs. Phenotypic Plasticity All acclimatization and acclimate is phenotypic plasticity, but not all phenotypic plasticity is acclimatization or acclimation Phenotypic Plasticity same genotype expresses different phenotypes Acclimatization: for the Acclimation: for the purpose of lessening purpose of lessening enviro. stress in nature stress in lab conditions 8 4 Phenotypic Plasticity: Morphs Phenotypic plasticity is often adaptive. Ex: two discrete morphs of Spadefoot frogs with different growth rates. Carnivore tadpoles: grow faster and metamorphose earlier. Favored in ephemeral ponds that dry up quickly. Omnivores: grow slower; favored in ponds that last longer (in more favorable conditions) and have higher chance of survival. 9 EX: Ponderosa pines Other times, plasticity is merely physiological (e.g., growth rate response to temperature) cool, moist climates: allocate more biomass to leaves (no risk of desiccation). Grow taller, thinner. warmer desert climates: allocate more biomass to sapwood (water transport). Short and stocky shape. 10 5 Life History Diversity “camouflage mismatch” in Timing of seasonal Snowshoe hare life history activities can be of critical importance, but may not keep pace with climate change. 11 Mode of reproduction is a basic life history trait 1. Asexual reproduction: Simple cell division (binary fission)—all prokaryotes and many protists. Some multicellular organisms reproduce both sexually and asexually (e.g., corals). 12 6  Mode of reproduction is a basic life history trait 2. Sexual reproduction: Most plants, animals, many fungi, and protists reproduce sexually. Isogamy: Gametes are equal in size (A). Anisogamy: Gametes differ in size(s)(B). Most common among multicellular organisms Usually the egg is much larger, contains nutritional material. 13 Sexual reproduction has disadvantages: An individual transmits only half of its genome to the next generation. Population growth rate is only half that of asexually reproducing species. Recombination and chromosome assortment during meiosis can break up favorable gene combinations. 14 7  Benefits of sexual reproduction: Recombination promotes genetic variation and better ability of populations to respond to environmental challenges. More “raw materials” for natural selection to act upon 15 In organism that can undergo both sexual and asexual reproduction (hermaphrodites), sexual reproduction is favored when exposed to a stressor. 16 8 Life History Diversity Complex life cycles: have at least two stages. Characterized by: - Different body forms/stage - Live in different habitats/stage - Eat different foods/stage 17 Metamorphosis: Abrupt transition in form between the larval and juvenile stages. Complex life cycles are common in insects, marine invertebrates, amphibians, and some fishes. Many parasites have evolved complex life cycles with specialized stages for each host. https://www.youtube.com/watch?v=uK_iZZ4Bx2o 18 9  Direct development—the fertilized egg develops into a juvenile without passing through a larval stage. 19 Trade-Offs There are trade-offs between life history traits. 1. Number and size of offspring 2. Amount of parental care 3. Age at reproduction and survival 21 10 There are trade-offs between life history traits. Trade-offs: Organisms allocate limited energy or resources to one function at the expense of another. Aboveground growth Flowering (reproduction) 22 Trade-Offs Trade-offs between size and number of offspring The larger the investment in each individual offspring, the fewer offspring can be produced. Investments: Energy, resources, time and loss of chances for other activities such as foraging. 23 11 Trade-Offs Lack clutch size: Maximum number of offspring a parent can successfully raise to maturity. Named for David Lack (1947) who noticed that bird’s clutch size increases with latitude; longer daylight hours may allow parents more time to forage and feed more offspring. Environmental conditions influence life history… 24 Trade-Off: Number of offspring vs. Survival of offspring Experimental manipulation of clutch size in lesser black-backed gulls In larger clutches, offspring have less chance of survival (Nager et al. 2000). 25 12 Trade-Offs Exist for Plants Too In species without parental care, resources are invested in propagules (eggs or seeds). Size of the propagule is a trade-off with the number produced. In plants, seed size is negatively correlated with the number of seeds produced. 26 Trade-Off: Reproduction vs. Growth Reproduction vs. growth: Allocating resources to reproduction can decrease an individual’s growth rate, survival rate, or potential for future reproduction. Douglas fir trees: thickness of annual growth rings declines in trees that produce many cones. 27 13 Life Cycle Evolution Organisms face different selection pressures at different life cycle stages. Different morphologies and behaviors are adaptive at different life cycle stages. Small early life stages are vulnerable, leading to various mechanisms to protect the small life stages. 29 Life Cycle Evolution Parental investment: Provisioning eggs or embryos—yolk and protective coverings for eggs, nutrient-rich endosperm in plant seeds Parental care—invest time and energy to feed and protect offspring 30 14 Life Cycle Evolution Dispersal: Movement of organisms or propagules from their birthplace. Small size is also beneficial: Marine snail species that could disperse tended to persist longer. 31 Life Cycle Evolution Dormancy: State of suspended growth and development in which an organism can survive unfavorable conditions. Small seeds, spores, eggs, and embryos are best suited to dormancy—less metabolic energy is needed to stay alive. Some larger animals also enter dormancy. https://www.you tube.com/watch ?v=PVNpSeutk 2I&t=23s 32 15 Life Cycle Evolution Functional specialization of stages is common in complex life cycles. Larval stage: feeding, growth, Dispersal, protection Adult stage: reproduction 33 Life History Continua Reproductive patterns can be classified along several continua. Number of reproductive events during an organism’s lifetime: Semelparous species reproduce only once. Annual plants, plants such as the agave, and Giant Pacific octopus. Iteroparous species can reproduce multiple times; most animals, many kinds of plants. 34 16 Life History Continua r-selection and K-selection describe two ends of a reproductive strategy continuum. r-selected species K-selected species “live fast, die young” “slow and steady” Short life spans, Long-lived, develop rapid development, slowly, late early maturation, low maturation, invest parental investment, heavily in each high reproduction offspring, low rates. reproduction rates 35 r or K? A B A B A B 36 17 r or K? K A B r A r B K A B r K 37 Life History Continua A classification scheme for plant life histories based on stress and disturbance (Grime 1977). Stress—any abiotic factor that limits growth. - Shortages of resources: Light, water, nutrients, temperature, other physical or chemical limitation Disturbance—any process (biotic or abiotic) that destroys plant biomass (or kills). - Things that damage/kill: Grazing, fire, frost, wind, erosion, ice, storms, etc. 39 18  superior ability to acquire light, minerals, water, and space short life span and rapid growth rates, slow exploit growth, low habitats palatabilty, after high disturbance adaptability 40 Can you compare ants to elephants? Charnov proposed a scheme that removes the influence of size and time. Get a dimensionless ratio (c). Increasing time to maturity 41 19  Bottom line: Charnov’s scheme may be most useful when comparing life histories across a range of taxonomy or size. Grime’s scheme may be best for comparing plant taxa. The r–K continuum is useful in relating life histories to population growth characteristics. 42 Summary life history is a record of events relating to its growth, development, reproduction, and survival. Differences may be genetically or environmentally based Lifecycles can be complex or simple There are always trade-offs Many strategies fall along the r-K continuum 43 20