BIO 115 1st Edition Lecture 32 Topic Discussed: PopulationLife history traits are products of natural selection- life history- comprises the traits that affect its schedule of reproduction and survivalo age at when reproduction beginso frequency of reproductiono number of offspring are produced during each reproductive cycle- Life history traits are evolutionary outcomes reflected in the development, physiology, and behavior of an organismEvolution and Life History Diversity- Semelparity (big-bang reproduction)- reproduce once and die; best in variable environments- Iteroparity (repeated reproduction)- produce offspring repeatedly; best in dependable environments“Trade-offs” - Organisms have finite resources, which may lead to trade-offs between survival and reproductiono trade-off between survival and paternal care in many birdso Tradeoffs exist between seed size and survival percentage in plantsMany factors that regulate population growth are density-dependent- There are two general questions about regulation of population growth- What environmental factors stop a population from growing indefinitely?These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Why do some populations show radical fluctuations in size over time, while others remain stable?Population Growth and Population Density- density-independent growth-birth rate and death rate do not change with population density- density-dependent growth- birth/death rates vary with population densityMechanisms of Density-Dependent Population Regulation- Density-dependent birth and death rates are an example of negative feedback that regulates population growtho are affected by many factors, such as competition for resources, territoriality, disease, predation, toxic wastes, and intrinsic factorsCompetition for Resources- In crowded populations, increasing population density intensifies competition for resources and results in a lower birth rate (ie. pollinators)- Toxic Wastes- accumulation of toxic wastes can contribute to density-dependent regulation of population size- Predation-as a prey population builds up, predators may feed preferentially on that species- Intrinsic Factors (physiological) -for some populations, regulate population size- Territoriality-in many vertebrates and some invertebrates, competition for territory may limit density- Disease-population density can influence the health and survival of organisms in the face of pathogenso In dense populations, pathogens can spread more rapidlyPopulation Dynamics- the complex interactions between biotic and abiotic factors that cause variation in population size- Populations of some species fluctuate in regular cycles; in others, cycles are less clearStability and Fluctuation- weather, food, disease, and predators can affect population size over time- Populations can cycle back and forth from small to large over time; cycles can appear chaotic or regular- Lag- when a population takes some time to react to disturbance Population Cycles: Three hypotheses have been proposed to explain the hare’s 10-year interval- Hypothesis 1: The hare’s population cycle follows a cycle of winter food supplyo Additional food was provided experimentally to a hare population, and the whole population increased in size but continued to cycle- Hypothesis 2: The hare’s population cycle is driven by pressure from other predatorso In a study conducted by field ecologists, 90% of the hares were killed by predators- Hypothesis 3: The hare’s population cycle is linked to sunspot cycleso Sunspot activity affects light quality (UV light intensity), which in turn may affectthe quality of the hares’ foodo There is a correlation between sunspot activity and hare population size in some studies, but not in allo Ie. sunspot activity tends to vary on an 11 year cycle, and hare populations vary incontrasting ways at the same time across continents- The human population is no longer growing exponentially but is still increasing rapidly- Growth rate is declining- Great leap forward-huge decline in growth rate- result of urbanizationRegional Patterns of Population Change- To maintain population stability, a regional human population can exist in one of two configurationso Zero population growth = High birth rate – High death rateo Zero population growth =Low birth rate – Low death rate- The demographic transition -move from the first configuration to the second o associated with an increase in the quality of health care and improved access to education (especially for women)Global Carrying CapacityPopulation ecologists predict a global population of 7.8-10.8 billion people in 2050- Kaverage =10–15 billionLimits on Human Population Size- The ecological footprint concept summarizes the aggregate land and water area needed tosustain the people of a nation- It is one measure of how close we are to the carrying capacity of Earth- we can regulate our population growth through social