NS 201 Lecture 3.2 - Population Ecology 2 PDF

NS 201 - Lecture 3.2: Population Biology II - Demographics & Life History Dr. Jenni Austiff NS201, Team U 20 Sept. 2023 Reminders… Complete week 4 readings 4.1 - Bio2e: Ch 45.4, 45.5 4.1 - Serengeti: Nature’s Living Laboratory (HHMI video) 4.2 - Bio2e: Ch 46.1, 46.2 4.2 - Some...

NS 201 - Lecture 3.2: Population Biology II - Demographics & Life History Dr. Jenni Austiff NS201, Team U 20 Sept. 2023 Reminders… Complete week 4 readings 4.1 - Bio2e: Ch 45.4, 45.5 4.1 - Serengeti: Nature’s Living Laboratory (HHMI video) 4.2 - Bio2e: Ch 46.1, 46.2 4.2 - Some Animals Are More Equal than Others: Keystone Species and Trophic Cascades (HHMI video) Collect your Sample Data for Lab 1: Part C Quiz 1 (3%) opens Friday, 2:30pm due Wednesday, Sept 25 by 1:00pm One hour time limit Send me accommodations letters ASAP Lecture 3.2 - Outline 1.What is Demography? 2.Life Tables & Survivorship Curve 3.Life History Traits Population Characteristics Knowing the size, density, and distribution of a population are important factors we can use to ask many questions As we count individuals we can also make observations and/or take measurements of various traits of individuals What are some traits you might document about individuals in a populations? What questions might this allow you to ask about a population? We can also ask questions about how populations change over time and the structure of populations This information can be useful for studying Population Demography and Population Life History Demography Demography → statistical study of how a population changes over time Population size (N) depends on… increase the population size Birth rates (B) Immigration → joining a population decrease the population size Death rates (D) Emigration → leaving a population Factors Affecting Growth Population size & health large populations can be more stable, but can also be more vulnerable to disease and competition, etc. Age structure what proportion of the population is at reproductive age Sex ratio (i.e. reproductive sex) reproduction, especially in many vertebrates, is often limited by the number females (in this case, egg producing individuals) Generation time how long before an individual can reproduce (age of 1st reproduction) length of reproductive lifespan, frequency of reproduction average number of offspring per event or individual Life Tables Life Table → summary of age-specific survival pattern of a population Divide the population by age and sex Shows the probability of living vs. dying at different age intervals of an animal’s life Why is this important? Knowing how many individuals survive through their reproductive years is important for understanding if a population is growing or shrinking Life Tables Belding’s Ground Squirrels Survival What can we learn from this data? Survivorship Curve What can we learn Belding’s Ground Squirrels Survival from this data? Survivorship Curves Survivorship curve → a plot of the proportion of a cohort alive at each age What type of curve are the ground squirrels? What types of organisms do you expect to follow Curves I & III? Survivorship Curves Type I → low infant mortality, higher death rates late in life e.g. humans, many large mammals - few offspring, high parental investment Type II → individuals tend to die at steady rates throughout life e.g. small mammals and birds - moderate amount of offspring, some parental investment Type III → low likelihood of surviving early life, but those that survive early life tend to live for relatively long e.g. trees, invertebrates - produce many small offspring, little to no parental investment Age Structure Demographic data can also be represented as a pyramid showing the proportion of a population at different age ranges Example showing human populations (based on different countries) at different stages of population growth trends Age Structure We can also compare this across time for a given population How has age structure of US human population changed? Life History Life History → describes age-, size-, or stage-specific patterns of development, growth, maturation, reproduction, survival and lifespan of an organism’s life cycle Examples of life-history characteristics reproductive characteristics - number of offspring, etc. major life-stage transitions - hatching, metamorphosis or puberty aging (senescence), overall length of life Energy Budget Energy budget → organisms have a finite amount of energy to use for different essential life functions and must balance energy in and energy out Energy in → photosynthesis, food consumption Energy out → waste energy storage growth/development maintenance reproduction activity (foraging, evading predators, etc.) Energy Budget Energy budget proportions vary amongst organisms Depends on size, diet, activities, environment, method of thermoregulation (regulation of body temperature) Endotherm → generates own heat Ectotherm → gets heat from environment (e.g. sun) Life History Trade-Offs Because organisms have limited energy, they cannot invest the optimum amount of energy in any one activity Trade-Off → when an increase in one life history trait (improving fitness) is coupled to a decrease in another life history trait (reducing fitness) Types of Life History Trade-Offs number vs. size of offspring parental care vs. fecundity (i.e. fertility) offspring investment vs. parental survival Reproductive Trade-Offs Many types of life history trade-offs are related to reproduction Reproduction is energy intensive! What do you think is better… producing many or few offspring? producing large or small offspring? Reproductive Trade-Offs It depends! - different organism have evolved to prioritize different costs and benefits in reproductive strategies Eleutherodactylus coqui Lithobates sylvatica Native to Puerto Rico, high Native to U.S. northeast and Canada, investment (large eggs, father lower investment (small eggs, no protects eggs) in a small number parental care) in a large number of small of large offspring offspring Reproductive Trade-Offs Even within a species there can be variation on clutch size and offspring size, that comes as a trade-off Variation within Chickadee clutches What is the correlation between offspring size and clutch size? Fecundity Trade-Offs Fecundity → potential reproductive capacity of an individual within a population (i.e. number of offspring they can have) Higher fecundity usually means lower investment in individual offspring Lower fecundity usually means higher investment in individual offspring only so much energy to spend on reproduction Number of offspring vs. parental investment → trade-off! Reproduction and Survival Trade-Offs Reproduction is costly! It also has costs to a parent organism’s survival and longevity… European kestrel What is the relationship between brood size and parental survival? Reproductive Strategies Reproduction is costly! Organisms must balance several different factors in their reproductive strategies*… Reproduce fewer, larger offspring or more, smaller offspring? Give more care to fewer offspring or less care to more? Reproduce early at a smaller size or later at a larger size? live long and reproduce periodically vs. life fast and reproduce explosively once? Iteroparity vs. Semelparity *Organisms differ in their reproductive and life history traits. Sometimes these are referred to as “strategies”, but they are not conscious decisions. They are traits that have evolved over long periods of natural selection. Reproductive Strategies Iteroparity → reproduce multiple times throughout life survival through multiple reproductive seasons is likely generally occurs under stable or predictable environmental conditions variation between species in frequency of reproduction, clutch size, offspring size, parental care, etc. includes all birds, most reptiles, virtually all mammals, most fish, many insects, perennial plants Water Bear Pine tree Hippopotamus Reproductive Strategies Semelparity → organism reproduce only once before dying, use most of their resource budget on one reproductive event often all members of a population reproduce at the same time, overwhelming predators often an adaptation to erratic or unpredictable environments with low survival in adulthood many offspring, usually with little or no parental investment occurs in a variety of animals and plants (i.e. annuals) Pacific Salmon Sunflower Cicadas Life History of K- and r-selected Species Species’ reproductive strategies, habitat, and behavior (esp. resource acquisition and care of young) interact with length of life and survivorship factors to shape population growth two general patterns of population growth (more on this next week! for now we will just discuss reproductive patterns) Driven by growth rate (r) Driven by carrying capacity (K) Carrying Capacity Carrying Capacity (K) → max number of organisms that a region can support without environmental degradation (more on this next week) r -Selected Species r-selected → explosive, exponential reproduction selected by unpredictable or changing environments many, small offspring with low to no parental investment offspring are relatively self-sufficient at birth/hatching Puffball mushroom Thimble Jellyfish American toad K - Selected Species K-selected species → tend to exist close to carrying capacity selected by stable, predictable environments few, large offspring with high parental investment high intraspecific competition - competition between members of the same species (more on this later) Oak Tree Orca Many types of birds Is this chameleon species r or K-selected? Jackson’s Chameleon typically have clutches of 8-30 offspring. They give live birth. Babies can feed immediately after hatching. They take 5-8 months to sexually mature and live 5-10 years. Is this species of chameleon r or K selected? Overall, chameleons are more of an r-selected species ??? Many species may have a mix of r and K related traits! r vs. K Selection Summary In reality, biology is often more of a continuum or a mix of traits within a generalized category Reminders… Complete week 4 readings 4.1 - Bio2e: Ch 45.4, 45.5 4.1 - Serengeti: Nature’s Living Laboratory (HHMI video) 4.2 - Bio2e: Ch 46.1, 46.2 4.2 - Some Animals Are More Equal than Others: Keystone Species and Trophic Cascades (HHMI video) Collect your Sample Data for Lab 1: Part C Quiz 1 (3%) opens Friday, 2:30pm due Wednesday, Sept 25 by 1:00pm One hour time limit Send me accommodations letters ASAP