Chapter 12 Lecture 2

Question 1

Populations have…

Answer 1

growth limits

Question 2

what may regulate populations

Answer 2

the effects of density-independent factors or density dependent factors

Question 3

density-independent factors

Answer 3

temp., precipitation, catastrophes; whose effects operate without regard to density

Question 4

density-dependent factors

Answer 4

whose effects increase with increased density

Question 5

what are density-independent factors sometimes referred to as

Answer 5

extrinsic factors… and most frequently affect “r” selected species

Question 6

density-dependent factors are sometimes referred to as

Answer 6

intrinsic factors… and most frequently affect “K” selected species

Question 7

Density independent

Answer 7

factors that limit population size regardless of the population’s density

Question 8

common factors of density independent limitations

Answer 8

climactic events (tornadoes, floods, extreme temperatures, droughts)

Question 9

Andrewarth and Birch

Answer 9

challenged density-dependent regulation of population size

Question 10

the natural regulation of animal numbers by david lack

Answer 10

the importance of density-dependent factors in shaping population size English ornithologist

Question 11

the distribution and abundance of animals by H.G. Andrewartha and L.C. Birch (Australian entomologists)

Answer 11

they argued that most populations, particularly those of insects and other small invertebrates, are influenced primarily by density independent factors - and that periods of favorable environmental conditions - ultimately control the size of populations

Question 12

andrewartha and birch were largely influenced by

Answer 12

a study on populations of thrips (small insects that feed on plant parts)

Question 13

brings ideal conditions for thrip population growth (good combination of moisture, warmth and plant flowering)

Answer 13

the spring in Australia - October through December

Question 14

not only did the number of thrips follow seasonal changes in weather, but

Answer 14

the peak density of the population varied with climate from year to year. Food supply apparently had little to do with variations in the population

Question 15

what did andrewartha and birch observe

Answer 15

1. at no time were the numbers of thrips so dense to outstrip their food supply
2. the variation in the population was accounted for satisfactorily by the physical conditions of the environment

Question 16

what did andrewartha and birch claim

Answer 16

most of the evidence came from simplified and controlled lab populations, and had dubious application in natural populations

Question 17

what did andrewartha and birch suggest

Answer 17

the demonstration of density dependence does not necessarily imply regulation of the population by density-dependent factors. one must show under natural conditions that such factors cause dense populations to the decrease and allow sparse populations to increase

Question 18

who challenged Davidson and andrewartha’s data directly

Answer 18

frederick smith

Question 19

what did smith argue

Answer 19

that davidson and andrewartha had analyzed their data in such a way that they couldn’t have detected density dependence

Question 20

what did smith point out

Answer 20

arguments about density dependence do not address the absolute size of a population at a particular time of year; rather, they relate changes in population size to the initial size of the population

Question 21

what did smith assume

Answer 21

the thrips had exponential growth, and that changes in the size of N may be represented by increments of the logarithm of N

Question 22

how did smith poke additional holes in andrewartha’s argument

Answer 22

looking at the variances of the averages of his data

Question 23

what did smith show

Answer 23

the variance in the log N declined between October and November, which suggest a lack of independence between the variables

Question 24

density dependent

Answer 24

factors that affect population size in relation to the population’s density

Question 25

negative density dependence

Answer 25

when the rate of population growth decreases as population density increases

Question 26

the most common factors that cause negative density dependence are

Answer 26

limiting resources (food, nesting sites, physical space)

Question 27

as a population’s size increases…

Answer 27

resources are divided among more individuals, and per capita resources decline to a level at which individuals find it difficult to grow and reproduce

Question 28

what do crowded populations

Answer 28

generate stress, transmit disease, and attract predators

Question 29

how do water fleas influence one another less directly

Answer 29

by eating the same resources (each water flea consumes millions of single-celled green algae and diatoms)

Question 30

fecundity (progeny per female per day) of water fleas as a function of age at different densities

Answer 30

fecundity decreased as density increased

fecundity also decreased with increasing female age at each density level

Question 31

the geometric rate of population growth (lambda) calculated from the water flea life tables decreased linearly with

Answer 31

increasing density and fell below 1.0 at a density of about 20 individuals per cm3

Question 32

territorial behavior in many kinds of animals regulates population size in a…

Answer 32

density-dependent fashion

Question 33

what does territorial behavior force

Answer 33

the young to socially subordinate individuals to leave the local population and seek space elsewhere (and possibly forego reproduction)

Question 34

negative density-dependence in plants

Answer 34

when plants are grown at high densities, each plant has access to fewer resources such as sunlight, water, and soil nutrients

Question 35

self-thinning curve

Answer 35

a graphical relationship that shows how decreases in population density over time lead to increases in the size of each individual in the population; often has a slope of -3/2

Question 36

positive density dependence

Answer 36

when the rate of population growth increases as population density increases (aka inverse density dependence, or allee effect)

Question 37

when does positive density dependence typically occur

Answer 37

when population densities are low, which may make it hard to find mates, particularly when sex ratios are uneven

Question 38

what can low densities lead to

Answer 38

harmful effects of inbreeding and a higher predation risk

Question 39

what are populations often regulated by

Answer 39

both positive and negative density dependence

Question 40

what do increased densities provide

Answer 40

more individuals for breeding

Question 41

above some density, resources become limiting and…

Answer 41

negative density dependence begins to play a role