2.1 - Species And Populations

Question 1

Define species

Answer 1

A species is a group of organisms sharing
common characteristics that interbreed and
produce fertile offspring.

Question 2

Define habitat

Answer 2

A habitat is the environment in which a species normally lives.

Question 3

Define niche

Answer 3

A niche describes the particular set of abiotic
and biotic conditions and resources to wnich an
organism or population responds

Question 4

Define fundamental niche

Answer 4

The fundamental niche describes the full range
or conditions and resources in which a species could survive and reproduce. The realized niche
describes the actual conditions and resources in
which a species exists due to biotic interactions

Question 5

Define abiotic

Answer 5

The non-living, physical factors that influence the organisms and ecosystem, ep temperature sunlight, pH, salinity, precipitation are termed
abiotic factors

Question 6

Define biotic factors

Answer 6

The interactions between the organisms, eg predation, herbivory, parasitism, mutualism, disease, competition are termed biotic factors.

Question 7

Define population

Answer 7

A population is a group of organisms of the same
species living in the dame area at the same time and which are capable of interbreeding

Question 8

What do s and j curves describe

Answer 8

S and J population curves describe a generalized
response of populations to a particular set of conditions (abiotic and biotic factors).

Question 9

What is an ecosystem made up from

Answer 9

Ecosystems are made up of the organisms and physical environment and the interactions between the living and non-living components within them.

Question 10

What are 3 examples of species

Answer 10

Humans, giraffes, and pine trees

Question 11

How is a population of snails defined

Answer 11

Snails of one species in a pond form a population but the snails in another pond are a different population. A road or river may separate two populations from each other and stop them interbreeding.

Question 12

Define population density

Answer 12

Population density is the average number of individuals in a stated area, for example gazelles km-2, or bacteria cm-3,

Question 13

What are 3 factos affecting population size

Answer 13

• natality (birth rate),
• mortality (death rate), and
• migration:
• immigration (moving into the area)
emigration (moving out of the area.

Question 14

What biotic factors allow an organism to have a niche

Answer 14

• every relationship that organism may have
• where it lives
• how it responds to resources available, to predators, to competitors
• how it alters these biotic factors.

Question 15

What abiotic factors allow an organism to have a niche

Answer 15

• how much space there is
• availability of light, water etc.

Question 16

Can 2 species have the same niche
- plus an example

Answer 16

No two species can inhabit the same ecological niche in the same place at the same time: if many species live together they must have slightly different needs and responses so are not in the same niche.
For example, lions and cheetahs both live in the same area of the African savanna but they hunt different prey. Lions typically take down bigger herbivores such as zebra and Cape Bullalo whereas cheetahs will focus on the smaller antelopes such as the Thompson’s gazelle and impalas.

Question 17

Define fundamental niche

Answer 17

Fundamental niche describes the full range of conditions and resources in which a species could survive and reproduce.

Question 18

Define realised niche

Answer 18

Realized niche describes the actual conditions and resources in which a species exists due to biotic interactions.

Question 19

What does a limiting factor do
- plus an example

Answer 19

Limiting factors prevent a community, population or organism growing larger. There are many limiting factors which restrict the growth of populations in nature. Examples of this are phosphate being in limited supply (limiting) in most aquatic systems, and low temperature in the tundra which freezes the soil and limits water availability to plants.
Limiting factors will slow population growth as it approaches the carrying capacity of the system.

Question 20

Define carrying capacity

Answer 20

Carrying capacity is the maximum number of a species or ‘load’ that can be sustainably supported by a given area

Question 21

Define population dynamic

Answer 21

Population dynamics is the study of the factors that cause changes to population sizes.

Question 22

How does a habitat change

Answer 22

No organism can stay the same: it grows, eats, ages and dies. All habitats change too. Animals enter and leave it, plants grow and shade the ground, water flows into and out of it. Animal migration may change a habitat greatly. Fire, natural disasters and human activities all change ecosystems. Interactions between individuals, populations and communities change ecosystems too.
Each species influences the population sizes of others and the carrying capacity of the environment for that species.

Question 23

What happened in Madagascar which changed hábitats

Answer 23

Plagues of locusts can devastate all vegetation in their path including our crops. In 2013, a severe locust plague hit Madagascar with many swarms, each with over 1 billion locusts. The rice crop, livestock and rare wild animals were at risk and only aerial spraying of insecticide stopped some of the damage.

Question 24

When does competition take place in a ecosystem

Answer 24

All the organisms in any ecosystem have some effect on every other organism in that ecosystem. Also any resource in any ecosystem exists only in a limited supply. When these two conditions apply jointly, competition takes place.

Question 25

Define Intraspecific competition

Answer 25

Intraspecific competition is between members of the same species. When the numbers of a population are small, there is little real competition between individuals for resources. Provided the numbers are not too small for individuals to find mates, population growth will be high.

Question 26

How does population growth affect Intraspecific competition

Answer 26

As the population grows, so does the competition between individuals for the resources until eventually the carrying capacity of the ecosystem is reached. In this situation, often the stronger individuals claim the larger share of the resources.

Question 27

How do some species deal with intraspecific competition

Answer 27

Some species deal with intraspecific competition by being territorial, eg deer. An individual or pair holds an area and fends off rivals. Individuals that are the most successful reproductively will hold the biggest territory and hence have access to more resources, and will be more successful at breeding.

Question 28

How does intraspecific competition affect population numbers

Answer 28

Intraspecific competition tends to stabilize population numbers. It produces something called a sigmoid or logistic growth curve which is S-shaped

Question 29

Define Interspecific competition

Answer 29

Interspecific competition: Individuals of different species could be competing for the same resource. Interspecific competition may result in a balance, in which both species share the resource. The other outcome is that one species may totally out-compete the other: this is the principle of competitive exclusion. An example of both of these outcomes can be seen in a garden that has become overrun by weeds. A number of weed species coexist together, but often the original domestic plants have been totally excluded.

Question 30

Define predation

Answer 30

Predation is when one animal, the predator, eats another animal, the prey. Examples are plenty, like lions eating zebras and wolves eating moose. The predator kills the prey. Be aware that not only animals eat other animals, some plants (insectivorous plants) consume insects and other small animals.

Question 31

Define herbivory

Answer 31

Herbivory is defined as an animal (herbivore) eating a green plant. Some plants have defence mechanisms against this, for example thorns or spines (some cacti), a stinging mechanism (stinging nettles), or toxic chemicals (poison ivy). Herbivores may be large (eg elephants, cattle) or small (eg larvae of leaf miner insects that eat the inside of leaves) or in between (eg rabbits).

Question 32

Define parasitism

Answer 32

Parasitism is a relationship between two species in which one species (the parasite) lives in or on another (the host), gaining its food from it. Normally parasites do not kill the host, unlike in predation. However, high parasite population densities can lead to the host’s death. Examples of parasites are vampire bats and intestinal worms.

Question 33

Define mutualism

Answer 33

Mutualism is a relation between two or more species in which all benefit and none suffer. It is a form of symbiosis (living together). The other types of symbiosis are parasitism (above) and commensalism (when one partner is helped and the other is not significantly harmed, eg an epiphyte such as an orchid or fern growing half-way up a tree trunk).

Question 34

State an example of mutualism

Answer 34

Another example is the relationship between leguminous plants (beans, clover, vetch, peas) and nitrogen-fixing bacteria - Rhizobium. The bacteria live inside root nodules in the legumes. They absorb nitrogen from the soil and make it available to the plant in the form of ammonium compounds. The plants in turn supply the bacteria with sugar from photosynthesis. This mutualistic relationship enables legumes to live on very poor soils. As a consequence, leguminous plants are among the earliest pioneer species during succession on poor soil. Clover is also often used to increase the nutrient content of agricultural soil.

Question 35

What is exponential or geometric growth

Answer 35

Over time the numbers within a population change. If we were to collect a few bacterial cells, place them in a suitable supply of nutrients and then, under a microscope, count the number of cells every hour, we would find that there would be many more bacteria at the end of a 24-hour period than at the start. Bacteria can reproduce asexually by splitting in two (binary fission) so, if you start with one bacterium, there will be 2,4,8, 16,32,64 etc. if there are no limiting factors slowing growth. This is called exponential or geometric growth

Question 36

Define s-curves

Answer 36

S-curves start with exponential growth. No limiting factors affect the growth at first. However, above a certain population size, the growth rate slows down gradually, finally resulting in a population of constant size.

Question 37

Explain the growth of yeast using figure 2.1.10 (s-curve)

Answer 37

The graph in figure 2.1.10 illustrates this for a colony of yeast grown in a constant but limited supply of nutrient. During the first few days the colony grows slowly as it starts to multiply (lag phase) then it starts to grow very rapidly as the multiplying colony has a plentiful nutrient supply (exponential phase). Eventually the population size stabilizes as only a set number of yeast cells can exploit the limited resources (stationary phase). Any more yeast cells and there is not enough food to go around. The numbers stabilize at the carrying capacity of the environment which is the maximum number or load of individuals that an environment can carry or support.

Question 38

Where is the carrying capacity represented on a s curve

Answer 38

The maximum population size is called the carrying capacity (K) of the ecosystem. The area between the exponential growth curve and the S-curve is called environmental resistance.

Question 39

Define j curves

Answer 39

J-curves (see figure 2.1.11) show a ‘boom and bust’ pattern. The population grows exponentially at first and then, suddenly, collapses. These collapses are called diebacks. Often the population exceeds the carrying capacity on a long-term or continuing basis before the collapse occurs (overshoot). It is important to note ‘long-term basis’ as the carrying capacity can be exceeded in the short term. It seems likely that the human race is overshooting its carrying capacity at the moment.

Question 40

What are some problems with s and j curves

Answer 40

The J-curve does not show the gradual slowdown of population growth with increasing population size.

A J-shaped population growth curve is typical of microbes, invertebrates, fish and small mammals.

S- and J-curves are idealized curves. In practice, many limiting factors act on the same population and the resulting population growth curve normally looks like a combination of an S- and a J-curve.