Chapter 8

1. Chapter 8 Population Ecology

2. Types of Species in Communities • Native species • species that normally live in a particular community • Nonnative species • also referred to as “invasive” or “alien” species • species that enter a new community either through immigration or introduction • Introduction may be deliberate or accidental • i.e. “killer bees,” Kudzu, zebra mussels, Asian oysters, domesticated animals

3. Indicator Species • species whose decline or migration indicates a significant change (damage) to a particular community • Serve as “early warning sentinels” of environmental degradation • Examples: • Amphibians • Trout • Birds • Aquatic macroinvertebrates

4. Keystone Species • species whose removal from its community may dramatically alter the structure and function of the community • roles: • pollinators • top predators • decomposers

5. Foundation Species • species that alters its habitat in ways that benefit other species • behaviors of such species may influence succession and increase species richness • sometimes identical to the keystone species, while other times serves as a counterbalance • Examples: elephants, kelp, eastern hemlock, mussels

6. Population Distribution • Three general patterns: (see below) • Most populations live in clumps although other patterns occur based on resource distribution. Figure 8-2

7. Why Clumping? • Resource availability varies from place to place. • Living in herds, flocks, or schools provides protection from predators and population declines. • Fish, birds, caribou, antelope, zebra • Predators that live in groups are afforded a better chance of catching prey and getting a meal. • Wolves, hunting dogs • Temporary animal groupings may occur for mating and caring for young. • Dolphin, albatross

8. Changes in Population Size • Populations increase through births and immigration • Populations decrease through deaths and emigration

9. Population Age Structure: • How fast a population grows or declines depends on its age structure. • Prereproductive age: not mature enough to reproduce. • Reproductive age: those capable of reproduction. • Postreproductive age: those too old to reproduce. • Populations with mostly reproductive individuals tend to increase. • Populations with mostly post-reproductive individuals tend to decrease. • Stable populations are equitability distributed among all three categories.

10. Limits on Population Growth: Biotic Potential vs. Environmental Resistance • No population can increase its size indefinitely. There are always limits to population growth in nature. • Population change is a balance between: • Biotic potential - the intrinsic rate of increase (r) or the rate at which a population would grow if it had unlimited resources and… • Environmental resistance – all the factors that act to limit the growth of a population. • Together these determine a populations carrying capacity (K): the maximum population of a given species that a particular habitat can sustain indefinitely without degrading the habitat.

11. Exponential and Logistic Population Growth: J-Curves and S-Curves • Exponential or geometric growth – starts slowly but accelerates rapidly as population increases • J-shaped curve plotted on a graph of population vs. time • Logistic growth – exponential growth followed by a steady population decrease until the population size levels off • S-shaped curve • Usually levels off at or near the carrying capacity • Carrying capacity is not fixed

12. Environmental Resistance Carrying capacity (K) Population size (N) Biotic Potential Exponential Growth Time (t) Fig. 8-3, p. 163

13. Population Growth Curves • Exhibit four phases • Lag – phase characterized by low birth rates, when the population is adjusting to a new environment • Growth – phase which shows a dramatic increase in population size (B+I > D+E) • Stationary – phase when then population is in dynamic equilibrium (B+I = D+E) • Death – phase in which the population declines (B+I < D+E)

14. Can a Population Exceed Its Carrying Capacity? • Members of populations which exceed their resources will die unless they adapt or move to an area with more resources. • Some populations overshoottheir carrying capacity. • Reproductive time lag • Causes a dieback or a crash • Some populations may increase their carrying capacity by developing adaptive traits (i.e. natural selection) • Some species maintain their carrying capacity by migrating to other areas.

15. Overshoot Carrying capacity Number of sheep (millions) Year Fig. 8-4, p. 164

16. Population overshoots carrying capacity Population Crashes Number of reindeer Carrying capacity Year Fig. 8-6, p. 165

17. Population Density and Population Change: Effects of Crowding • Population density: the number of individuals in a population found in a particular area or volume. • A population’s density can affect how rapidly it can grow or decline. • Density dependent factors include biotic factors like disease, competition for resources, predation, and parasitism • Some population control factors are not affected by population density. • Density independent factors include abiotic factors like weather, fire, pollution, and habitat destruction

18. Types of Population Change Curves in Nature • Population sizes may stay the same, increase, decrease, vary in regular cycles, or change erratically. • Stable: fluctuates slightly above and below carrying capacity. • Irruptive: populations explode and then crash to a more stable level. • short-lived, rapidly reproducing species (i.e. algae, insects) • Cyclic: populations fluctuate according to regular cyclic or boom- and-bust cycles. • close predator-prey interactions • Irregular: erratic changes possibly due to chaos or drastic change. • populations that inhabit unstable or highly variable environments

19. Hare Lynx Population size (thousands) Year Fig. 8-7, p. 166

20. REPRODUCTIVE PATTERNS • Some species reproduce without having sex (asexual). • Offspring are exact genetic copies (clones). • Others reproduce by having sex (sexual). • Genetic material is mixture of two individuals. • Disadvantages: males do not give birth, increase chance of genetic errors and defects, courtship and mating rituals can be costly (energetically). • Major advantages: promotes genetic diversity, division of labor among the sexes may provide offspring greater protection through critical periods.

21. Reproductive Patterns:Opportunists and Competitors • r-selected species: Large number of smaller offspring with little parental care • K-selected species: Fewer, larger offspring with higher invested parental care Figure 8-9

22. Reproductive Patterns • r-selected species tend to be opportunists while K-selected species tend to be competitors. Figure 8-10

23. Survivorship Curves: Short to Long Lives • The way to represent the age structure of a population is with a survivorship curve. • Late loss population live to an old age. • Constant loss population die at all ages. • Most members of early loss populations, die at young ages. Number of individuals age

24. WORK CITED Population Ecology. (1998) Cyber Ed.