Lecture 19: Life History & Population Dynamics PDF

Lecture 18. Life history & population dynamics  Principle of allocation Acquisition of resources – each individual organism acquires a finite - amount of resources ↑ Resources are allocated to required life processes: basic maintenance,...

Lecture 18. Life history & population dynamics  Principle of allocation Acquisition of resources – each individual organism acquires a finite - amount of resources ↑ Resources are allocated to required life processes: basic maintenance, growth, repair, resource acquisition, escaping predators, reproduction, etc. Principle of allocation When resources are abundant: extra resources allocated to growth, reproduction, etc. When resources are scarce (conditions are stressful): resources allocated to basic maintenance – little or none allocated to other processes/activities Principle of allocation Y R = resources P = proportion of R invested in survival 1 – P = proportion of R invested in reproduction met fired aslet you reporte pete Y-model of resource allocation trade-offs Alonso-Alvarez Can you relate this to range limits? Alonso-Alvarez Life History Life history – the schedule of organism’s growth, development, reproduction, & survival Life history traits evolve to maximize an organism’s fitness Natural selection favors traits that - improve an organism’s survival & reproductive success Life history traits – traits that affect an organism’s life history - Life history traits include: Age at sexual maturity Frequency of reproduction Number & size of offspring Size at birth Growth rate Investment in parental care Age-specific survival rate Dispersal behavior Life history traits – traits that affect an organism’s life history Life history traits include: Age at sexual maturity Frequency of reproduction Number & size of offspring Y Size at birth Growth rate Investment in parental care Age-specific survival rate Dispersal behavior Life history Reproductive strategies – Semelparity Semelparity – organism reproduces once before death afte they reproduce they die. Semelparity favored by selection when environment is unpredictable & survival rate of offspring is low Salman Salmon returns from ocean to stream in which it was born– lays 1000s of eggs then dies – complete sacrifice of health to reproduce ‘Century plant’ (agave) flowers & produces seeds once in its life  seahorse All of male salmon’s resources allocated to reproduction – immune system repressed – sustained high levels of corticosteroids cause system failure, gastrointestinal failure, & death Male salmon allocates all resources to 1 reproductive event – then dies Reproductive strategies – Iteroparity (itero- Latin ‘again’) Iteroparity – organism reproduces multiple times before death example humans they reproduce of many as they car Iteroparous organisms invest in fewer, larger offspring – survival rate of offspring is higher Life history trade-offs Trade-off exists between reproduction & survival Reproduction always has a cost – energy put into reproduction cannot be used for growth, repair, etc. Life history trade-offs Female red deer in Scotland that reproduced in summer were more likely to die the following winter Eurasian kestrels (falcons) that have more chicks have a higher chance of dying the following winter Why do you think survival rate of males was lower than females? Life history strategies: K-selection & r-selection K-selected - carrying species – present in stable & predictable capacity environments (populations near carrying capacity) Examples: bison, elephants, humans, whales, coconut palms, etc. Life history strategies: K-selection Characteristics of K-selected species: Produce fewer offspring Longer gestation periods ↑ Greater parental care * Life history strategies: K-selection & r-selection r-selected species – in unstable or unpredictable environments where offspring have low chance of survival (less likely to reach K) Examples: ‘weeds,’ grasses, insects, rodents, etc. * produce quickly  r Characteristics of r-selected - species: Produce many offspring (high r) - Small body size - Short time to maturity - Short generation time- Little parental care- Life history strategies: K-selection & r-selection r-selected K-selected Number of offspring many few Offspring size & small large Age at 1st reproduction younger older Mortality rate high low Lifespan short & long Parental care none extensive Invasive species tend to be r-selected Invasive species – introduced species to an environment that becomes overpopulated & harms its new environment – displace native organisms tend to be R Seletive harm emiroment Tend to have high r & do well in disturbed environments fend to do will to the point they warmit they Factors that regulate population growth Density-independent factors – effects of factors do not depend on pop. density - Examples: floods, fires, drought, human development, etc. Density-dependent factors – effects of factors depend on population density Examples: competition, predation & herbivory, parasitism & disease, etc. Density-independent factors that affect population growth Effects of factors do not depend on population density Seasonal cycles (warm & cold, wet & dry) Natural disasters (floods, drought, fire, volcanos, etc.) Human effects (clear-cutting, damming, paving, etc.) Density-independent regulators of population growth Sierra Grasshopper (Xanthippus sierra) – up to 10,000+ feet el. in Sierra Nevada Entire adult population dies in winter – population persists as eggs underground Sonora Pass (el. 10,000 ft.) Density-independent factors: natural disasters (floods, fire, volcanos, etc.) Mt. St. Helens before & after its 1980 eruption (southwest Washington) Density of tree populations had no bearing on whether they survived the eruption Mt. St. Helens erupting (left) & flattened trees after eruption (right) Density-independent factors: human effects (clear-cutting, damming, paving, etc.) Hetch Hetchy Valley – Tuolumne River – before & after damming (1923) Population density of a species of plant would have had no impact on survival after the dam was built. Modern trail along Hetch Hetchy Reservoir Density-independent factors: human effects (clear- cutting, damming, paving, etc.) Clear-cutting of forests – every tree in an area cut down & removed Density-dependent factors that regulate population growth Physiological factors Parasitism & disease Competition Predation & herbivory Waste accumulation Territoriality Density-dependent regulators of population growth Intrinsic physiological factors can regulate population size At high densities: Increase in aggressive interactions Hormonal changes that delay sexual maturation & depress immune system Intrinsic physiological factors can regulate population size At high densities: white- footed mice will not breed – even when food & shelter are abundant  Density-dependent factors – Competition two put *Competition – use of a shared, limited resourceits or organism share a add more food Competition – use of a shared, limited resource – limitation reduces survival and/or reproduction If resource is not limited, there will be no competition (e.g., organisms - do not compete for atmospheric oxygen) - If resource is not shared, there will be no competition - Mountain lions & bobcats compete somewhat for prey, but they mostly eat prey of different sizes Less sharing of resource = less competition More sharing of resource = more competition Intraspecific competition – competition within species - Interspecific competition – competition between species - - Male sage grouse compete with cattle for food, but not for mates Density-dependent factors – Competition Song sparrows on Mandarte Island, BC: clutch size (no. eggs laid) decreases as density of females on island increases Intraspecific competition for food seems to limit population size Experiment: when extra food supplied, clutch size did not decrease – even at high population densities sparrow lay more egg when there they not enough food more. food Limiting factors cause population to reach carrying capacity (to stop growing) Intraspecific competition for limited resources causes population to reach K N Density-dependent factors Waste accumulation – metabolic wastes accumulate at high population densities High concentrations of wastes become toxic or spread disease Density-dependent factors – waste accumulation Example: Brewer’s yeast (Saccharomyces cerevisiae) produces ethanol as a byproduct consuming carbohydrates Yeast can tolerate alcohol concentration - of ~13% before they begin to die Alcohol content of wine is usually