2.1 - Species And Populations Flashcards
Define species
A species is a group of organisms sharing
common characteristics that interbreed and
produce fertile offspring.
Define habitat
A habitat is the environment in which a species normally lives.
Define niche
A niche describes the particular set of abiotic
and biotic conditions and resources to wnich an
organism or population responds
Define fundamental niche
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
Define abiotic
The non-living, physical factors that influence the organisms and ecosystem, ep temperature sunlight, pH, salinity, precipitation are termed
abiotic factors
Define biotic factors
The interactions between the organisms, eg predation, herbivory, parasitism, mutualism, disease, competition are termed biotic factors.
Define population
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
What do s and j curves describe
S and J population curves describe a generalized
response of populations to a particular set of conditions (abiotic and biotic factors).
What is an ecosystem made up from
Ecosystems are made up of the organisms and physical environment and the interactions between the living and non-living components within them.
What are 3 examples of species
Humans, giraffes, and pine trees
How is a population of snails defined
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.
Define population density
Population density is the average number of individuals in a stated area, for example gazelles km-2, or bacteria cm-3,
What are 3 factos affecting population size
• natality (birth rate),
• mortality (death rate), and
• migration:
• immigration (moving into the area)
emigration (moving out of the area.
What biotic factors allow an organism to have a niche
• 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.
What abiotic factors allow an organism to have a niche
• how much space there is
• availability of light, water etc.
Can 2 species have the same niche
- plus an example
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.
Define fundamental niche
Fundamental niche describes the full range of conditions and resources in which a species could survive and reproduce.
Define realised niche
Realized niche describes the actual conditions and resources in which a species exists due to biotic interactions.
What does a limiting factor do
- plus an example
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.
Define carrying capacity
Carrying capacity is the maximum number of a species or ‘load’ that can be sustainably supported by a given area
Define population dynamic
Population dynamics is the study of the factors that cause changes to population sizes.
How does a habitat change
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.
What happened in Madagascar which changed hábitats
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.
When does competition take place in a ecosystem
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.
Define Intraspecific competition
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.
How does population growth affect Intraspecific competition
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.
How do some species deal with intraspecific competition
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.
How does intraspecific competition affect population numbers
Intraspecific competition tends to stabilize population numbers. It produces something called a sigmoid or logistic growth curve which is S-shaped
Define Interspecific competition
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.
Define predation
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.
Define herbivory
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).
Define parasitism
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.
Define mutualism
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).
State an example of mutualism
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.
What is exponential or geometric growth
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
Define s-curves
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.
Explain the growth of yeast using figure 2.1.10 (s-curve)
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.
Where is the carrying capacity represented on a s curve
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.
Define j curves
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.
What are some problems with s and j curves
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.
