Chapter # 11 – Population Regulation (pg. 223 – 237)

1. Chapter #11 – Population Regulation (pg. 223 – 237)

2. ( k – N ) dN r N = (1 – ) dt k N k dN r N = dt Chapter #11 – Population Regulation (pg. 223 – 237) 11.1 – The Environment Functions to Limit Population Growth. The Logistic Model of Population Growth or

3. Population Dynamics Logistic Growth • Environmental Resistance can reduce the reproductive rate and average life span and increase the death rate of young. • As Environmental Resistance increases, population growth slows and eventually stops, likely near (k).

4. Carrying Capacity Finite Resources? Carrying Capacity (k): The abundance (size) of a species’ population that a habitat can support for a specified period of time (an upper limit). Source: Bolen and Robinson (1999) Wildlife Ecology and Management

5. Environmental Resistance? Finite Resources ? Environmental Resistance: The limiting influences of environmental factors on the numbers of individuals in a community. Source: Bolen and Robinson (1999) Wildlife Ecology and Management

6. Chapter #11 – Population Regulation (pg. 223 – 237) 11.2 – Population Regulation Involves Density-Dependence. • As population density increases, individuals compete for space, energy, and nutrients. • At carrying capacity, each individual's share of resources is just enough to allow it to replace itself in the next generation. • At carrying capacity the birth rate (b) = death rate (d). • Carrying capacity (k) is determined by the continuous availability of resources.

7. Environmental Resistance (ER) • Environmental Resistance (ER) can be classified into two broad categories: • Density-independent factors • Density-dependent factors

8. Environmental Resistance (ER) A factor that causes higher mortality or reduced birth rates as a population becomes more dense is referred to as a density-dependent factor.

9. Density-Dependence • Density-dependent factors become more effective as population density increases. • Exert negative feedback effect on population size.

10. Density-Dependence Density-Dependence (DD) • “A factor that causes • higher mortality or • reduced birth rates as a • population becomes more dense” • (Bolen & Robinson) • disease, food supply, • predation, and • territorial behavior High Per Capita Birth Rate Low Low High Population Density

11. Population Dynamics Population Cycles • Predation - involves a predator killing a prey organism to consume. • Predators exert density-dependent controls on a population. • Increased prey availability can increase birth rates and/or decrease death rates of predators. • Prey population losses will increase.

12. Population Regulation Population Cycles

13. Prey Switching and Availability - Interactions

14. Chapter #11 – Population Regulation (pg. 223 – 237) 11.3 – Competition Results when Resources Are Limited. • Describes the interaction among individuals who attempt to utilize a resource that is limited relative to the demand for it. • Competition intensifies as populations grow and near carrying capacity. • For two organisms to compete, they must share the same resource(s).

15. Competition for Resources • Competition may be divided into two groups based on the species identity of the competitors: • Interspecific competition is between individuals of different species. • Intraspecific competition is between individuals of the same species. 11.3 – Competition Results when Resources Are Limited.

16. Competition for Resources • Competition may also be divided into two types based on the nature of the interaction: • Scramble (exploitative) competition is a free-for-all scramble as individuals try to beat others to a limited pool of resources. • Contest (interference) competition involves social or chemical interactions that limit a competitor’s access to resources.

17. Competition for Resources • Competition may also be divided into two types based on the nature of the interaction: • Scramble (exploitative) competition is a free-for-all scramble as individuals try to beat others to a limited pool of resources (direct or indirect – respond to depressed resource levels). • Contest (interference) competition involves social or chemical interactions that limit a competitor’s access to resources (direct interaction).

18. Density-Independence • Density-independent factors limit populations regardless of their density • Examples: climate, weather, floods, fires, pesticide use, pollutants, and overhunting.

19. Density-Independence Density-Independence (DI) No association with population density – they act on a population independent of density - e.g., weather (floods, hurricanes) fires, earthquakes, volcanoes Per Capita Birth Rate Population Density

20. Chapter #11 – Population Regulation (pg. 223 – 237) 11.4 – Intraspecific Competition Affects Growth and Development. • As populations density increases toward a level of insufficiency (per unit for basal metabolism), individuals can reduce food intake. • Reduced food intake slows individual growth. • Reduce growth can lead to reduced reproductive output and success. • Thus, there is an inverse relationship between density and rate of body growth.

21. Chapter #11 – Population Regulation (pg. 223 – 237) 11.4 – Intraspecific Competition Affects Growth and Development.

22. Chapter #11 – Population Regulation (pg. 223 – 237) 11.5 – Intraspecific Competition Can Reduce Reproduction.

23. Chapter #11 – Population Regulation (pg. 223 – 237) 11.6 – High Density Is Stressful to Individuals. • As population density increases, space becomes restricted. Aggressive behavior (competition for space) becomes more frequent. • Increased crowding and social contact can cause stress, triggering hormonal changes that restrict reproduction and growth. • Increased stress may also lead to immune system suppression and increased frequency of disease. • Thus, there may be reduced births and increased deaths.

24. Chapter #11 – Population Regulation The Chitty Hypothesis 11.6,7 –The Chitty hypothesis depends upon having two types of individuals in the population. One is tolerant of having other individuals close by (ie, tolerant of high densities) and has a low reproductive rate. The second type is intolerant and tends to disperse from the population under conditions of high density. They also have a higher reproductive rate than the tolerant individuals.

25. Home Range: an area in which an animal normally lives and is not necessarily associated with any type of aggressive behavior. Dominance hierarchy may exist among individuals with overlapping home ranges. Territory: a defended, more or less fixed and exclusive area maintained by an individual or social unit occupying it. Chapter #11 – Population Regulation (pg. 223 – 237) 11.8,9 – Social Behavior May Function to Limit Populations. Territoriality Can Function to Regulate Growth.

26. Chapter #11 – Population Regulation (pg. 223 – 237) 11.8,9 – Social Behavior May Function to Limit Populations. Territoriality Can Function to Regulate Growth (limit access).

27. Chapter #11 – Population Regulation (pg. 223 – 237) 11.10 – Plants Preempt Space and Resources – Are They “Territorial”? • Preventing root invasion can be a form of competition. Big Sagebrush (Artemisa tridentata)

28. Chapter #11 – Population Regulation (pg. 223 – 237) 11.11 – Density-Independent Factors Can Influence Population Growth.

29. Chapter #11 – Population Regulation (pg. 223 – 237) 11.11 – Density-Independent Factors Can Influence Population Growth.

30. Ultimately . . . . • The abundance of a population at any given time is the result of complex interactions between density-independent and density -dependent forms of environmental resistance.

31. Next Time . . . . Interspecific Competition