Chapter 9 Population Ecology

Core Case Study: Southern Sea Otters: Are They Back from the Brink of Extinction? They were over-hunted to the brink of extinction by the early 1900’s and are now making a comeback. Figure 8-1

Core Case Study: Southern Sea Otters: Are They Back from the Brink of Extinction? Sea otters are an important keystone species for sea urchins and other kelp-eating organisms. Figure 8-1

POPULATION DYNAMICS AND CARRYING CAPACITY Most populations live in clumps although other patterns occur based on resource distribution. Do humans live in clumps? Figure 8-2

Populations change in size density and age distribution Most members of populations live together in groups or clumps. Why? Availability of resources varies from place to place Living in groups offers better protection from predators Some predators live in packs to hunt more efficiently Temporary groups may form for matting and carrying for young

Four variables influence/ govern population size Births aka natality Deaths aka mortality Immigration Emigration Which ones increase population size?

Age Structure: Young Populations Can Grow Fast 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.

Limits on Population Growth: Biotic Potential vs Limits on Population Growth: Biotic Potential vs. Environmental Resistance No population can increase its size indefinitely. The intrinsic rate of increase (r) is the rate at which a population would grow if it had unlimited resources. Carrying capacity (K): the maximum population of a given species that a particular habitat can sustain indefinitely without degrading the habitat.

Exponential and Logistic Population Growth: J-Curves and S-Curves Populations grow rapidly with ample resources, but as resources become limited, its growth rate slows and levels off. Figure 8-4

Exponential and Logistic Population Growth: J-Curves and S-Curves As a population levels off, it often fluctuates slightly above and below the carrying capacity. Figure 8-4

Exceeding Carrying Capacity: Move, Switch Habits, or Decline in Size Members of populations which exceed their resources will die unless they adapt or move to an area with more resources. Figure 8-6

What four factors have the greatest influence on limiting populations? Light Water Nutrients Competition or predation

Exceeding Carrying Capacity: Move, Switch Habits, or Decline in Size Over time species may increase their carrying capacity by developing adaptations. Some species maintain their carrying capacity by migrating to other areas. So far, technological, social, and other cultural changes have extended the earth’s carrying capacity for humans.

Types of Population Change Curves in Nature Population sizes often vary in regular cycles when the predator and prey populations are controlled by the scarcity of resources. Figure 8-7

Carrying capacity is the ________. Maximum population size that a given environment can sustain Greatest number of different niches possible in a given area Potential growth in the number of species in a given area Limitation on numbers of species in a community Average number of offspring carried to term by a species

Unregulated populations tend to increase by ______. Linear growth Exponential growth Pyramidal growth Emigration Immigration

A logistic growth curve depicting a population that is limited by a definite carrying capacity is shaped like the letter ___. J L M S N

In a population of field mice, an example of an adaptive trait that could help with reproduction and/or survival would be ____ Being brightly colored so other mice can see you Having a higher metabolism Spending more time running around looking for better seeds Having a bit more fur to withstand colder weather Having shorter legs to be closer to the ground

Which of the following types of species is least vulnerable to habitat fragmentation? Generalists Specialists Large predators Migratory species Keystone species

Population Density and Population Change: Effects of Crowding Population density: the number of individuals in a population found in a particular area or volume. What is a density-dependent factor? What is a density-independent factor?

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. Cyclic: populations fluctuate and regular cyclic or boom-and-bust cycles. Irregular: erratic changes possibly due to chaos or drastic change.

What is the hypothesis of bottom-up control? What is the hypothesis of top-down control?

Case Study: Exploding White-Tailed Deer Populations in the United States Since the 1930s the white-tailed deer population has exploded in the United States. Nearly extinct prior to their protection in 1920’s. Today 25-30 million white-tailed deer in U.S. pose human interaction problems. Deer-vehicle collisions (1.5 million per year). Transmit disease (Lyme disease in deer ticks).

What are the 2 types of reproduction? Asexual- each cell divides and results in an identical clone of the original cell; no genetic recombination Sexual- gametes from each parent combine to produce offspring with a combination of genetic traits from each parent

What are the 3 disadvantages to sexual reproduction? Males do not give birth; Females have to produce twice the offspring to maintain population size Chances of genetic errors/ defects increase during splitting/ recombination. Courtship & mating consumes energy and time, transmit disease and inflict injury on males in some cases.

What are the two advantages of sexual reproduction? Genetic diversity helps ensure survival of species in the face of environmental changes. Males may help with food gathering and/or rearing of offspring.

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

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

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 population, die at young ages.

Survivorship Curves: Short to Long Lives The populations of different species vary in how long individual members typically live. Figure 8-11

What is a life table/ actuary table?

Variations in genetic diversity can affect the survival of small, isolated populations. What is the founder effect? A few individuals move to a new location that is isolated from the original population. There is limited genetic diversity. http://www.pbs.org/wgbh/evolution/library/06/3/l_063_03.html

What is a demographic bottleneck? A few individuals survive a catastrophic event. What is a genetic drift? Random changes in gene frequencies in a population. Why does inbreeding effect a population's viability? Increases the number of defective genes in a population.

Humans have directly affected changes on about ___% of the earth’s land surface. What are 9 of the major ways humans have altered nature to meet their own needs? Destruction and degradation of habitats has reduced biodiversity. Homogenization of natural ecosystems by clearing land and planting only one species (monoculture) Destruction of the earth’s net primary productivity.

4) Certain types of intervention have unintentionally strengthened pest species and disease causing bacteria. 5) Some predator species have been deliberately eliminated from ranching areas. 6) Alterations have occurred due to the introduction of nonnative species. 7) Renewable resources have been over-harvested. 8)Some human activities interfere with normal chemical cycling and energy flows in the environment. 9) We are increasingly dependent on nonrenewable energy that pollutes the environment.

Which of the following is generally true of K-strategist species as compared to r-strategist species? They reach sexual maturity earlier They have more young They are more likely to be invasive species They have longer life spans Their population cycle are more rapid

Density-dependent factors ________ Include the effects of a hard freeze on an entire community Include the effects of a hard freeze on a single species within a community Cause decreases in the number of species in an ecosystem Include the effects of disease on an entire community Include the effects of disease on a single species within a community

One examply of artificial selection is ____ Gypsy moths as an invasive species Pet dogs that have gone wild, are mating, and live in packs A liger Popcorn Humans placing a gene for human insulin in a flower

Groups of organisms with low biotic potential, such as grey whales, are said to be ______. r-selected K-selected Density-independent organisms Density-dependent organisms Because of their size, grey whales actually have high biotic potential

Which of the following best describes the survivorship curve you would expect to find for a fish? Late loss Constant loss Early loss No loss None of these answers