Chapter 26 Population Growth and Regulation 1 Ecology Ecology the study of the interrelationships of organisms with each other and with their non living enviornment What factors effect population size Populations change through births deaths or migration Immigration migration into the population Emigration migration out of the population 26 1 2 How Does Population Size Change In most natural populations birth and death rates are the primary factors that influence population size 26 1 26 1 3 How Does Population Size Change Two major opposing factors determine birth and death rates Biotic potential the theoretical maximum rate at which a population could increase Assumes ideal conditions for maximum birth and minimum death Environmental resistance curbs on population growth set by the living and nonliving enviornment 26 1 4 How Does Population Size Change Biotic potential is influenced by several factors 1 The age of reproductive maturity 2 The frequency of reproduction 3 The average number of offspring 4 The length of reproductive lifespan 5 The death rate under ideal conditions 26 1 5 Biotic potential vs environmental resistance Exponential growth a pattern of continuous increase in population size If births exceed deaths by a constant Percentage you get a j curve 26 1 26 2 6 Biotic potential vs environmental resistance The effect of death rate Assumes bacterial population doubles every 20 min 26 1 26 3 7 How is population growth regulated Population growth cannot continue indefinitely In other words exponential growth is only possible under certain conditions Boom and bust cycles When environmental resistance is reduced 26 2 8 Boom and bust cycles 26 2 Fig 26 4 9 Boom and bust cycles 26 2 Fig 26 4 10 When environmental resistance is reduced you can also see periods of exponential growth Increased food Elimination of predators The whooping crane was protected in 1940 26 2 Fig 26 5 11 Environmental resistance limits population growth Logistic population growth Result of environmental resistance Characterized by an S curve Carrying capacity the maximum population size that can be sustained by an ecosystem for an extended period without damage to the eco system 26 2 12 Logistic population growth 26 2 Fig 26 6 13 Logistic population curve in nature Ocean currents carry barnacle larvae to rocky seashores Eventually competition for space limits population growth 26 2 Fig 26 8 14 What if a population exceeds its carrying capacity 26 2 15 What if a population exceeds its carrying capacity 26 2 Fig 26 6 16 What if a population exceeds its carrying capacity Ex Reindeer introduced onto an island with no large predators 26 2 Fig 26 7 17 Environmental resistance usually maintains populations at or below their carrying capacity Factors that generate environmental resistance fall into two categories 1 Density independent factors 2 Density dependent factors 26 2 18 Density independent factors Factors that limit populations regardless of the population density Weather and climate Responsible for most boom and bust population cycles Habitat destruction by humans 26 2 19 Density dependent factors Factors that become more effective as the population density increases Predators Parasites Competition for resources 26 2 20 Density dependent factors predators Predators are organisms that eat other organisms prey Predator prey relationships can result in out of phase population cycles 26 2 Fig 26 11 21 Density dependent factors parasites Parasites Feed on a larger host animal causing harm Spread more rapidly among dense populations Weaken their host making them susceptible to death and less likely to reproduce 26 2 22 Density dependent factors Competition for resources Interspecific competition competition among individuals of different species Intraspecific competition competition among individuals of the same species 26 2 23 Density dependent factors Competition for resources Intraspecific competition scramble competition 26 2 Fig 26 12 24 So how are populations distributed Ecologists recognize three major types of spatial distribution Fig 26 14 26 3 25 How is the human population changing 26 4 Fig 26 16 26
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