30 Living in Ecosystems
30.1
Population Growth (p. 714; Figs. 30.1,
30.2, 30.3)
A. Groups of interacting organisms of the same species within a given area are called a population.
B. Characteristics of populations include population size (number of individuals), population density (number per unit area), population dispersion, and population growth.
C. The Exponential Growth Model
1.
Populations have the
capacity to grow.
2.
The biotic potential
(r) or innate capacity for increase is a theoretical value indicating the rate
at which the population can increase when there are no limits to its growth.
3.
This includes births
plus immigrants and deaths plus emigrants:
r = (births +
immigrants) - (deaths + emigrants)
4.
The innate capacity
for increase for a population is exponential.
5. When a small population is added to a new area of very favorable habitat, growth rate will be nearly exponential, as indicated by the following equation: Population growth rate = rN
where r = realized rate of population increase and N =
population size.
6. Exponential growth does not last long; at some point, the living space or food or shelter becomes limited, and the population growth rate slows down.
D. Carrying Capacity
1.
As the population
reaches the carrying capacity of its habitat, the growth rate slows to a near
standstill.
2. Carrying capacity is defined as the number of individuals the habitat is able to support indefinitely.
E. The Logistic Growth Model
1.
This type of growth
can be represented by the logistic growth equation:
Population growth rate = rN (K -
N/K)
where K = the carrying capacity, r = realized rate of population increase, and N = population size, as before.
2. This type of growth can best be represented by a sigmoid growth curve showing that growth is rapid at first when the population is small, then tapers off at an increasing rate as population size approaches carrying capacity..
30.2
The
Influence of Population Density (p. 717; Fig. 30.5)
A. Density-Independent Effects
1. Density-independent effects regulate population size regardless of the density of individuals.
2. Density-independent factors are primarily those associated with weather.
B. Density-Dependent Effects
1. As the population size approaches the carrying capacity, the amount of competition for living space, food, and mates becomes more fierce.
2. Changes in the nature and amount of competition that occur as population sizes increase are density-dependent effects.
C. Maximizing Population Productivity
1. In ecosystems that are exploited by humans, the aim is to maximize productivity by harvesting the population early in the rising portion of its growth curve where the point of maximal sustained yield lies.
30.3
Communities
(p. 720; Fig. 30.8)
A. All the populations of a given area make up a community.
B. We recognize a community largely because of the presence of its dominant species, but many other kinds of organisms are also characteristic of each community.
C. A community exists in a place because the ranges of its species overlap there.
30.4
The Niche
and Competition (p. 721; Fig. 30.9)
A. Each organism plays a role within its ecosystem.
B. Its role is called a niche—its way of interacting with others in its community and with its ecosystem.
C. The Realized Niche
1. The entire range of factors an organism could potentially exploit is its fundamental niche.
2. However, fundamental niches are rarely realized in nature because other organisms are present that use similar resources.
3. Competition over resources occurs, and an organism's niche is narrower than its true potential.
4. We say this is the realized niche.
30.5
Competitive
Exclusion (p. 722; Fig. 30.10)
A. In the 1930’s, ecologist Gause studied competition in three species of Paramecium and formulated his principle of competitive exclusion.
B. Niche Overlap
1. Experiments have shown that when there is niche overlap, two species can survive, but their niche breadth is narrowed.
C. Competitive Exclusion
1. When two species compete intensely, sometimes one can be excluded from the habitat, a process called competitive exclusion.
2. This can be seen in mature ecosystems where organisms rarely occupy their fundamental niche and, instead, share resources with their neighbors.
Resource Partitioning (p. 723; Figs. 30.11, 30.12)
A. Competitive exclusion is rare in nature because organisms evolve slight differences in food choice and habitat preference when competition is strong.
B. Sympatric species partition available resources through character displacement, reducing competition.
30.6
Coevolution and Symbiosis
(p. 724; Fig. 30.13)
A. Since organisms continually interact within their ecosystem, they coevolve with one another.
B. Symbiosis Is Widespread
1. In symbiosis, two species live in intimate contact with each other.
2. All symbiotic relationships carry the potential for coevolution between the organisms involved.
3. Examples of symbiosis include lichens, mycorrhizae, and leafcutter – fungi associations.
C. Kinds of Symbiosis
1. Types of symbiosis include commensalism, mutualism, and parasitism.
30.7Commensalism (p.
725; Figs. 30.14, 30.15)
A. In commensalism, one species benefits from the association, but the other neither benefits nor is harmed.
B. Examples of Commensalism
1. Several examples can be found in marine organisms.
2. Barnacles riding around on whales benefit by receiving food and protection, and the whale is not harmed.
3. Tropical fish receive protection from sea anemones and eat their leftovers, and the sea anemones are not harmed.
C. When Is Commensalism Commensalism?
1. There are no clear boundaries between commensalism and mutualism, and it is sometimes difficult to determine whether one or both species benefit.
30.8Mutualism (p. 726; Fig. 30.16)
A. Mutualism is a symbiotic, cooperative effort between two species.
B. Lichens are made up of an alga and a fungus, and both derive benefit from the association.
1. The fungus is fed by the alga, and the fungus protects the alga from drying.
C. Ants and Acacias
1. The mutualistic association between ants and certain tropical species of Acacia plants is a striking example of this kind of relationship.
2. The ants derive food and shelter from living in thorns of the plants, and the plants outcompete surrounding plants because the ants remove nearby shading leaves and contribute organic matter with nitrogen to the plant.
30.9Parasitism (p. 727; Fig. 30.17)
A. Parasitism is a symbiotic association in which the parasite benefits by deriving food and shelter from the host, and the host is harmed somewhat by having to feed the parasite.
B. External Parasites
1. External parasites, or ectoparasites, are common, such as lice or mosquitoes.
2. Parasitoids are insects that lay eggs on living hosts and are common among wasps.
C. Internal Parasites
1. Vertebrates are parasitized internally by endoparasites involving many different phyla of animals.
2. Internal parasitism is marked by extreme specialization.
D. Brood Parasitism
1. Brood parasitism occurs as birds lay their eggs in the nests of other species.
30.10
Plant
Defenses Against Herbivores (p. 728; Fig. 30.18)
A. As one species changes, its predator must change also if it is going to keep up—a process known as coevolution.
B. How plants defend themselves from herbivores is an excellent example of coevolution.
C. Chemical Defenses
1. Plants can employ physical or chemical means to deter predators; the most important ones are chemical.
D. The Evolutionary Response of Herbivores
1. Most herbivores tend to avoid plants that taste bad or make them sick, but some have evolved means of tolerating the chemical and can then exploit the plant as a resource; such is the case with the caterpillars of cabbage butterflies.
30.11
Animal
Defenses (p. 729; Figs. 30.19, 30.20, 30.21)
A. Animals also sometimes employ toxic or distasteful chemicals to deter their predators.
B. Defensive Coloration
1. Some animals are poisonous and also tend to be brightly colored to warn predators to leave them alone; such warning coloration is called aposematic coloration.
2. Some animals instead evolve means to blend into their surroundings, called crytic coloration.
3. Camouflaged animals benefit by living a solitary life because it is more difficult to hide in groups.
C. Chemical Defenses
1.
The poison-dart frogs
of
2. Organisms benefit by advertising their defenses so that predators leave them alone.
30.12
Predator-Prey
Cycles (p. 730; Figs. 30.22, 30.23, 30.24)
A. Predation is the consuming of one organism by another.
B. Predator-prey interactions also show examples of coevolution.
C. Refuges Promote Cycles
1. Predators will often deplete populations of prey unless prey have a refuge in which they can hide.
2. Even if prey populations become very small, they can usually recover once predator pressure lets up.
3. In nature, predator and prey population sizes are cyclic.
4. Prey population sizes are limited by predator pressure; when predators are abundant, prey populations decline.
5. When predator populations decline, prey populations recover.
6. Predator population sizes increase in response to more available prey.
7. Predator populations are thus limited by their food supply.
D. Cycles in Hare Populations: A Case Study
1. Population cycles, such as that described above, have been observed in hares and lemmings.
E. Predation Reduces Competition
1. The predators greatly reduce competitive exclusion, and this increases diversity, by reducing the numbers of individuals of competing species.
2. It is a mistake to try to eliminate the top predator from a community of organisms.
3. Predation helps to prevent prey populations from being driven to extinction.
4.
Community Stability
(p. 734)
30.13
Ecological
Succession (p. 734; Figs. 30.27, 30.28)
A. A community of organisms can be viewed as a web of competitive interactions, but the community had to develop those interactions over time.
B. Secondary Succession
1. Secondary succession occurs on areas that have been denuded of plant life, such as clear-cut forests and abandoned agricultural fields.
C. Primary Succession
1. When a bare rock or new habitat opens up, the first organisms reaching it are the pioneers.
2. They can grow and reproduce rapidly, and they have broad niches so they can survive easily over a wide range of conditions.
3. They form and improve the soil, and new arrivals move into the area.
4. The pioneers are not good at competition, so the new arrivals quickly displace them in the habitat.
5. Over time, still other, larger species of plants move in, until a climax community is reached.
6. The climax community is similar to the type of biome that exists in an area; it can endure over time.
7. This progression of one species replacing another over time is called succession.
8. Primary succession occurs on areas where nothing has ever grown before.
D. Why Succession Happens
1. Succession happens because species alter the habitat and the resources available in it through tolerance, facilitation, and inhibition.
30.14
Biodiversity
(p. 736; Figs. 30.29, 30.30)
A.
Some ecosystems are
more stable and resistant to disruption than others.
B.
Several factors
promote ecosystem stability.
C.
Species richness, or
biodiversity, is one factor that promotes stability in an ecosystem.
D.
Ecosystems that are
more biologically diverse, having more kinds of organisms, are generally more
stable than ecosystems with fewer types of species.
E.
Certain types of
disturbances might eliminate a few species, but the vast number of remaining
species can fill in the gap.
F.
However, there is a
point of no return.
G.
When the keystone
species for a diverse ecosystem is destroyed, the rest
of the community crashes as well, leading to the demise of the ecosystem.
H.
When we choose to
preserve ecosystem diversity, we are coming closer to preserving the entire
ecosystem.
I.
What Promotes
Biodiversity?
1.
A number of factors
promote biodiversity, including ecosystem size and latitude.
J.
Ecosystem Size
1.
Ecosystem size is
important.
2.
When an ecosystem is divided into smaller and smaller parcels, some of the
wider-ranging animals no longer have enough space to survive.
3.
Reducing
ecosystem size results in faunal collapse, the demise of many of the animal
species.
4.
National parks must be
large enough to promote diversity, and development near these parks should be
limited.
K.
Latitude
1. Latitude also promotes diversity around the equator where the areas receive more sunlight and have a longer growing season.
2. A longer growing season means more resources and more niche space, and climatic stability is an important factor as well because equatorial latitudes have not been subjected to glaciation.
30.15
Island
Biogeography (p. 738; Figs. 30.31, 30.32)
·
Define the term
“population.”
·
Explain how knowing a
population's size, density, and dispersion can give us information about the
success of the population in its habitat.
·
Know the exponential
growth equation and the logistic growth equation.
·
Understand how nearing
the carrying capacity of the habitat means increased density-dependent effects
for the population.
·
Contrast r-selected
population with K-selected populations.
·
List
density-dependent and density-independent factors that influence population
density.
·
Describe the three
different survivorship curves and give suitable examples of each.
·
Explain the
significance of each column in a life table.
·
Describe “niche.”
·
Understand how
competition can narrow the breadth of an organism's fundamental niche.
·
Explain what occurs
during competitive exclusion and resource partitioning.
·
Give examples of coevolutionary relationships in communities.
·
Discuss the three
types of symbiotic relationships that have coevolved over time.
·
List plant defenses
against herbivores.
·
Describe animal
defenses against predators.
· Explain how populations of predators cycle with those of their prey.
· Chapter 28 Reproduction and Development
28.1
Asexual and Sexual Reproduction (p. 662;
Figs. 28.1, 28.2)
A. Asexual reproduction is accomplished in certain animals by various means, such as budding or fission.
B. Sexual reproduction occurs as sperm and eggs are joined to produce a new individual.
C. Gametes are formed by meiosis in the gonads.
D. Different Approaches to Sex
1. Parthenogenesis is common to many arthropods and involves the production of eggs that develop into identical copies of the mother without fertilization.
2. Hermaphroditism occurs when one individual houses both ovaries and testes and can fertilize itself.
3. Numerous fish exhibit the tendency to change from one sex to the other due to environmental influences; protogyny (first female, then male) and protandry (first male, then female) are fairly common.
E. Sex Determination
1. The SRY gene on the Y chromosome determines whether or not a developing embryo is male.
2. Once testes form in the embryo, they secrete testosterone that influences other male traits.
28.2
Evolution of
Reproduction Among the Vertebrates (p. 664; Figs. 28.3, 28.4, 28.5, 28.6,
28.7, 28.8)
A. External fertilization occurs in many animals and involves the female releasing eggs from her body (usually into the water), and a male fertilizing them with sperm.
B. Internal fertilization occurs as the male deposits sperm inside the body of the female.
C. Internal fertilization may be classified as oviparous, ovoviviparous, or viviparous.
D. Fish and Amphibians
1. In fish, fertilization is external, as it is in amphibians.
2. Eggs lack shells and undergo development in an aquatic habitat.
E. Reptiles and Birds
1. Birds and most reptiles lay water-tight eggs able to withstand desiccation on dry land.
2. Reptiles lay leathery eggs and then abandon them.
3. All birds practice internal fertilization and lay shelled eggs.
4. Birds generally show parental care of eggs and young.
F. Mammals
1. Female mammals undergo cycles in which they are fertile (“in heat”), called estrus.
2. Monotremes lay water-tight eggs, but all other mammals are viviparous, giving birth to live young.
3. Marsupials give birth to fetuses that are incompletely developed and complete development within a pouch.
4. Placental mammals retain their young for a longer period of development and nourish the growing fetus by a placenta.
26 The Nervous System
26.1 Evolution of the
Animal Nervous System (p. 612; Figs. 26.1, 26.2, 26.3)
A. Animals sense changes in the environment using sensory neurons, and react to those changes using motor neurons; these two types of neurons are linked by a nervous system.
B. Neurons in the brain and spinal cord are part of the central nervous system.
C. The peripheral nervous system consists of neurons leading to and from the central nervous system.
D. Invertebrate Nervous Systems
1. The simplest nervous systems that provide reflexes are found in the Cnidaria.
2. More complex nervous systems, such as those in the flatworms, provide associative activities.
3. The evolutionary path to vertebrates shows more complex sensory mechanisms, differentiation into central and peripheral nervous systems, differentiation of sensory and motor neurons, increased complexity of association, and elaboration of the brain.
26.6 Evolution of the Vertebrate Brain
(p. 620; Figs. 26.11, 26.12, 26.13)
A. Despite extensive study, scientists are still not certain how the brain performs many of its functions.
B. Fossil agnanthans from 500 million years ago showed evidence of the hindbrain (rhombencephalon), the midbrain (mesencephalon), and the forebrain (prosencephalon).
1. The hindbrain is an extension of the spinal cord devoted mostly to coordinating motor reflexes.
2. In more advanced vertebrates, the cerebellum, an extension of the hindbrain, plays an important role as a coordinating center.
3. The midbrain is devoted to the reception and processing of sensory information and includes the optic lobes.
4. Brains of fishes continue to grow throughout life, unlike the brains of other vertebrates that stop growing in infancy.
C. The Dominant Forebrain
1. Beginning with the amphibians, the forebrain becomes more developed and plays an increasing role in sorting out sensory input.
2. In reptiles, amphibians, birds, and mammals, the forebrain is composed of the diencephalon (consisting of thalamus and hypothalamus), and the telencephalon (cerebrum in mammals).