Zoology 101: Animal Biology Last Lecture Outline Lecture 39 1. Ecology2. Dispersal and Distributions3. Population EcologyCurrent Lecture 1. Population structure 2. Species interactions Population Structure • Characteristics of interest◦ Demography: study of population attributes and how they change over time ▪ Composition of populations▪ Rates that describe population change • Population structure ◦ Sex ratio: number of males to number of females ◦ Age Structure: percent of individuals in different age groups in a population▪ too young (pre-reproduction)▪ Reproduction▪ post reproduction• Graphs:◦ Urn shaped: few kids, many parents, more seniors. Non-growing or declining population◦ Pyramid: lots of kids, some parents, fewer seniors. Rapidly growing population◦ Bell shaped: some kids, more parents, few seniors. Slow (non-growing) population • Population Rates: ◦ Birth rate: number of births per population size▪ fertility rate: number of offspring/unit of time• generation time ◦ Death rate: number of deaths per population size▪ survivorship◦ Generation time: amount of time between birth of an individual and the birth of its offspring • Survivorship◦ cohort: group of individuals born at the same time ◦ Survivorship: tracks changes in the number of individuals in a cohort over time▪ survivorship curve ◦ Type1: Low death rate in early and middle life, increases in older age groups (humans)◦ Type 2: death rate constant (chipmunk)◦ Type3: High death rate in early, lower death rate for survivors (snails, clams)• Rate of increase ( r)◦ r= birth rate – death rate ▪ r ignores immigration and emigration ◦ model of exponential growth: (dN/dt)= r(max)N▪ N= Number of individuals in a population ▪ t=time ◦ Rate of increase ( r ) determines speed at which population size increases◦ as population size increase, resources can become limited. Population are not always ideal in other ways (disturbance, predators, catastrophe) • Controls on Population size◦ density- independent controls: doesn't depend on population ( natural disasters)◦ Density-dependent controls: depends on population size (prey that die when a predator is around)◦ Some populations will increase and then level off (logistic growth) ▪ carrying capacity (k): point of population stabilization ▪ (dN/dt)=rN* (K-N/K)Species Interactions • Intraspecific interactions: occurs within a species• Interspecific interactions: occurs between 2 or more species ◦ Predation◦ Symbiosis◦ Competition • Predation (+/-)◦ Carnivory, herbivory◦ For case of herbivory, prey does not always have to die • Defenses against predators:◦ Remarkable diversity of predator defense adaptations; likely and evolutionary force◦ Coevolutionary arms race (Life dinner
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