Ecology Notes Week 5
Ecology Notes Week 5 Bio 369
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This 6 page Class Notes was uploaded by Joseph Notetaker on Friday September 23, 2016. The Class Notes belongs to Bio 369 at Missouri State University taught by Brain Greene in Fall 2016. Since its upload, it has received 5 views. For similar materials see General Ecology in Biology at Missouri State University.
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Date Created: 09/23/16
Ecology Notes Week 5 Chapter 8 Life Histories o Life histories are collections of traits that reflect evolved strategies for enhancing survival and reproductive success in different environments Fecundity, or number of offspring, is an important life history trait. Why would the number of eggs laid by a female vary so much between species o An organism’s life history can be described by the events of its life cycle Lifespan Reproduction Timing Frequency Development and growth o Temporary Dormancy o Temporary dormancy can mitigate seasonal resource deficiencies o Inactivity helps conserve energy when resources are rare or conditions prevent activity o Seasonally defined Hibernation Estivation o Diapause involves a suspended period of development Obligate-genetically programmed Facultative-plastic response to variable environment Why are there so many life history strategies? Life history patterns vary among groups of organisms o Lifespans o Lifespans can vary dramatically within groups Labord’s Chameleon has the shortest lifespan of any terrestrial vertebrate (<1 year) Lives longer as an egg than as an adult Komodo Dragon matures in 8-9 years and can live to be 30 o Parity o Parity describes the number of times an individual reproduces over its lifetime Semelparity: Single reproductive event, usually followed by rapid senescence Iteroparity: Multiple reproductive events over lifetime o Parity strategies likely reflect adaptation to environmental variability Iteroparity may be favored in variable environments so that reproductive effort is spread out across good and bad years Bet Hedging strategy Semelparity may be an excellent strategy when adult survival probability is always low o Resource availability has a proximate influence on reproductive effort Contrasting strategies Income Breeding: energy for reproduction obtained during pregnancy Capital Breeding: energy required for reproduction is stored in advance o Energy optimization o Life history patterns evolve as ways to optimize energy distribution to different functions during an organisms’ life cycle o Life history: the optimal allocation of energy to growth, reproduction, and maintenance under particular environmental conditions o Because energy is limited in all environments, life history strategies involve trade-offs. o Responses can vary within and among populations with changing resource levels Life history characteristics often ‘co-vary’ along a “slow-fast” gradient of possibilities o Fast life history: r-selection o Early maturity, short life Rapid growth High fecundity Low parental investment Semelparous or few reproductive events o Slow life history: K-selection o Long life, delayed maturity Slow growth Low fecundity High parental investment Iteroparous Plant life histories reflect evolved responses to environmental factors o Three different patterns favored in contrasting situations o Ruderals (weeds): rapidly colonize disturbed sites (rapid growth, high dispersal, high reproductive rates) o Stress tolerators (desert plants): adapted to extreme environments- slow growth and conservation of resources, heavy use of asexual reproduction o Competitors (trees): adapted to constant and predictable environments-large size, late maturity, long lifespan Covariation of life history variables often results in trade-offs among energy budget components o Offspring size and number (more offspring leads to smaller size) o Survival and reproductive effort o Growth and number of offspring Selective forces: The benefit of current reproduction is costly to survival and future reproduction o High reproductive investment maximizes offspring number but reduces future reproductive effort by minimizing parental survival o Lifetime fitness of parents balances the survival trade-off Manipulation of European Kestrel nests provides evidence for a high survival cost to reproduction o Clutch size balances trade-off between adult survival and number of offspring produced o Optimal number of offspring is the one that yields the most offspring without jeopardizing adult survival Survival costs of reproduction were also high for female lizards o Females with eggs removed survived much better than those enduring a “sham” surgery without further manipulation Delaying reproductive maturity (and allocating more energy to growth) can lead to higher offspring production at a larger body size in organisms that have intermediate growth. o Qualtiy vs Quantity The survival of offspring may also be influenced by number of offspring o Magpies have a clutch size of 7 eggs o Adding or subtracting eggs reduces total offspring production o Why does adding eggs reduce the number of offspring fledged? o Each offspring has to compete with others for resources Humans: o Sometimes humans are the selective force: heavy harvest pressure has affected life histories of many marine fish o Sustained harvest of Cod in the North Atlantic has caused a decline in age at maturity Proximate and Ultimate Factors: o Phenotypic plasticity occurs when the expression of a trait is influenced by the environment o The range of possible expressions for a given trait is the reaction norm Plasticity: o Plasticity is generally higher in species exposed to variable environments than species from stable environments o Larvae respond to pond conditions by adjusting rate of development Stable water levels: grow to maximal size before metamorphosis Drying pond: accelerate development to transform at small body size Environment: Environmental differences can result in population-specific life histories Low elevation: high metabolism, Low energy stored High elevation: Lower metabolism, High energy stored Not all traits are plastic, experiments can sort out the sources of variation in life history traits 3 outcomes: o Offspring size adjusted o Litter size adjusted o Both adjusted Differences in life history traits among populations can be caused by proximate or ultimate factors Experiments can determine whether variation in specific traits is due to plasticity (proximate environmental influence) or genetics (an evolved response) o Creating mesocosms helps as it determines if the environment or genetics are responsible for variation Chapter 9 Reproduction Reproduction is an essential but variable function o Two modes produced different kinds of offspring Asexual: clones of the adult Sexual: mixture of genes from two separate parents o Each mode used to varying degrees but nearly all organisms reproduce sexually at least occasionally Asexual reproduction: o Asexual reproduction is faster and less costly than sexual reproduction Parthogenesis occurs when females produce offspring without mating Many types Rare in vertebrates but known from most groups Sexual Reproduction: o Sexual reproduction is costly Substantial energy devoted to sexual reproduction strategies Structures Competing for or attracting mates Parental care Fitness reduction through genetic mixing (cost of meiosis) o But sexual reproduction is beneficial to gene pools The substantial costs of sexual reproduction are offset by important genetic benefits Increased genetic variation Loss of undesirable alleles Resistance to pathogens Asexual reproduction does not produce these benefits o Variations Hermaphroditism: both gonads in one individuals Simultaneous Sequential Yields higher fitness than separate sex strategy-unless male and female functions differ Hermaphroditism favored if having both sexual functions is an advantage Separate sexes favored when sexual functions are incompatible and lower fitness potential of hermaphrodite o Sexual dymorphism Parasitic males Whether single or separate sexes, outcrossing is usually promoted over self- fertilization to avoid inbreeding depression Many hermaphrodites have mechanisms to avoid self-fertilization o Self-incompatibility genes in plants Dispersal of juvenile animals away from birth place increases distance between relatives Many animals recognize and avoid mating with inbred and/or genetically similar individuals o Sex determination Sex can be determined by two separate mechanisms Genetic sex determination Inheritance of sex chromosomes Many different patterns Environmental sex determination Temperature Sex ratios of population and social factors
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