Population Ecology:

1. Population Ecology: How Do Organisms Interact to Form Populations?

2. What is Ecology? • Environmental concern is not ecology. • However, studying vultures scavenging a lion kill is of interest to ecologists. • They are also interested in rats scavenging a dumpster in urban America.

3. Ecology is a Branch of Biology • Ecology • is the study of organisms in relation to their environment

4. Ecology is a Branch of Biology • Important key factors to remember about ecology: • It is not a social cause • It is not a movement • It is not a natural history • It is not an interesting story about animals in nature • It is a science • Ecology includes quantitative measurements and addresses energy needs, efficiencies and balances.

5. Foundations of Modern Ecology • Biogeography • Addresses location and environment of living organisms. • Environmental physiology • How does living in a particular environment affect an animal’s structure and function? • Limnology • Study of freshwater ponds and lakes. • Behavioral ecology • How does living in a particular area with a particular set of characteristics affect the way animals behave?

6. Foundations of Modern Ecology

7. Three Main Branches of Ecology • Population Ecology • Focuses on dynamic changes occurring in one population or species. • Systems Ecology • Studies the dynamics of complex ecological communities and is a holistic approach. • Applied Ecology • Newest branch • Predicts the outcomes of human activities and recommends courses of action to mitigate certain of those activities.

8. Major Task: Study Populations • Humanity has an innate and almost unlimited ability to procreate, but a limited ability to produce food. • Humans populations tend to grow and outstrip their ability to feed themselves. • Leads to problems.

9. Factors That Influence Population Size • Population growth rate • Determined by: • Natality or birth rate • Death rate • Also influenced by immigration and emigration. • Expressed mathematically: r = (b-d) + (i-e)

10. Factors to Consider When Studying Population • Straight forward expression of population size is absolute number. • Count up all the individuals in the population. • More frequently used is density. • The number of individuals per unit area.

11. Factors to Consider When Studying Population • Range • The geographic area in which a population or species lives. • Habitat • Includes the areas the species finds all its specific needs. • Determining the area of the habitat of a species can be difficult.

12. How Do Populations Grow? • Two opposing forces affect population size • Biotic potential: • a population’s ability to reproduce. • Environmental resistance. • Consists of factors that limit growth.

13. Exponential Population Growth • Under ideal conditions wherein environmental conditions are low, populations grow exponentially. • The more the individuals, the faster the population grows. • (dN/dt) rN

14. Logistic Population Growth • Initially populations will grow exponentially. • However, population growth will slow due it reaching a carrying capacity. • The number of individuals the environment can support.

15. Factors That Limit Population Growth • Density-dependent • The effect of the factor depends on the population density. • Examples: space, predators, disease and food

16. Factors That Limit Population Growth • Density-independent • Effect of this factor is unrelated to the density of the population. • Examples: drought, freezing temperatures

17. Two Patterns of Population Growth • Studying population size can help scientists predict how it might change. • K-selected: • Species that possess characteristics that allow them to typically live under stable conditions near their carrying capacities • R-selected: • Species possess characteristics that have them typically living in unstable conditions where they maximize their reproductive potential • Most species live somewhere in between

18. Two Patterns of Population Growth

19. Two Patterns of Population Growth

20. Age Structure Diagrams • The numbers of individuals in each age class are arranged in rows, starting with the youngest on the bottom. • Numbers separated by gender. • The length of the row indicates the number of individuals.

21. Age Structure Diagrams Based on these diagrams, what conclusions can you draw about these populations?

22. Populations Differ in Their Longevity Patterns • Two types of longevity patterns • Physiological • The life span of the individual under ideal conditions. • Ecological • The age to which an individual might be expected to live in a given environment.

23. How Do Populations Interact? • Populations share space with other populations • Leads to interactions among them and makes them interdependent. • Niche • All aspects of the biological and physiological environment that are important to a species.

24. When Populations Compete, Both are Harmed • Competitive exclusion principle • Two species cannot coexist while exploiting the same resources. • Examples: • Paramecium • Wasps • Barnacles

25. When Populations Compete, Both are Harmed • Resource partitioning • The use of resources that are scarce in a given environment by different species at different times, different places or in different ways.

26. Predator-Prey Interactions • One population benefits at the expense of the other. • Results in the fates of predator and prey populations being intimately intertwined.

27. Predator-Prey Interactions • Population size fluctuates due to this relationship • Prey populations may increase, followed by increases in predator populations, • followed by decrease in prey populations, followed by decrease in predator populations

28. Predator-Prey Interactions • Predation may lead to extinction • Seen with introduced species. • Two categories of predator-prey relationships. • Plant-herbivore • Herbivore-carnivore

29. Plant-Herbivore Interactions • Herbivores have developed adaptations to deal with fluctuations in available food supplies: • Put on extensive layers of fat during seasons of abundance. • Some will migrate to where food is available. • Others hibernate during seasons of hardship. • Respond to seasons of scarcity by making do with foods of relatively low nutritional value.

30. Plant-Herbivore Interactions • Plants respond to herbivores by: • Producing enough tissue for herbivores and still survive • Produce distasteful chemicals that deter further feeding • Produce chemicals that affect herbivores’ physiology

31. Herbivore-Carnivore Interactions • Compared to plant material, animal material is • Easier to digest • Energy and nutrients are more concentrated • Drawback: • Herbivores are mobile • Dangerous when cornered

32. Herbivore-Carnivore Interactions • Mimicry • When an animal resembles something that it is not • Looking like something in the environment that predators would avoid .

33. Mimicry • Two types: • Müllerian: • When different species, each of which is dangerous, announce their undesireableness to predators with similar coloration characteristics. • Batesian: • When one species benefits from resembling the coloration of a dangerous species as a strategy to confound or discourage predators.

34. Symbioses • When populations form intimate associations: • Three types: • Parasitism • Commensalism • Mutualism

35. Parasitism • One species benefits at the expense of the other • Examples: • Tapeworms • Mosquitoes • Generally does not result in extinction of the host • Can reduce population numbers

36. Commensalism • One species benefits while the other is seemingly unaffected. • Examples: • Sea anemones growing on the backs of crabs

37. Mutualism • Intimate relationships in which both species benefit. • Most fascinating and important relationships known in biology. • Example: • Flowers and pollinators