3. 1. 2 - What is a species?

Question 1

why is the concept of species important for biologists?

Answer 1

• can be used to measure biodiversity
• by looking for changes in the species, the effect of natural environmental changes and changes as a result of human activity can be monitored

Question 2

What is the morphological species concept?

Answer 2

a species definition based solely on the appearance of the organisms observed
- scientists would look closely at the inner and outer morphology of organisms to group them into species

Question 3

state the negative of the morphological species concept.

Answer 3

1. the appearance of an organism can be affected by many different things
2. there can be a huge amount of variation within a group of closely related organisms
   - for example, organisms with sexual dimorphism, the different sexes could be grouped into a completely different species

Question 4

define sexual dimorphism

Answer 4

when there is a great deal of difference between the appearance of the male and female of a species

Question 5

what is the reproductive/ biological species concept?

Answer 5

grouping species based on the reproductive behaviour of the organism

Question 6

what is the general definition of a species?

Answer 6

a group of organisms with similar characteristics that interbreed to produce fertile offspring

Question 7

what are the strengths to this general definition of a species?

Answer 7

• it overcomes issues such as sexual dimorphism

- is regarded as a good working definition for many animal species

Question 8

what are the limitations to this general definition of a species?

Answer 8

• populations of organisms of the same species may not interbreed simply because they are in different places, not because they are different species
• if two species can produce fertile offspring then they can be considered the same species (e.g lion and tiger) even when they are not

Question 9

what are the two definitions of a species that overcome the limitations of the general one?

Answer 9

1. a group of organisms with similar characteristics that are all potentially capable of breeding to produce fertile offspring
2. a group of organisms in which genes can flow between individuals

Question 10

what are the positives and negatives of the reproductive/ biological species concept?

Answer 10

adv:
- good working model for most animals

disadv:
- much less helpful when classifying plants (which frequently interbreed with similar species to form fertile offspring)

Question 11

what are the other definitions of a species?

Answer 11

1. ecological species model
2. mate-recognition species model
3. genetic species model
4. evolutionary species model

Question 12

what is the ecological species model?

Answer 12

• based on the ecological niche occupied by an organism

but niche definitions vary and many species may occupy more than one niche

Question 13

what is the mate-recognition species model?

Answer 13

• based on unique fertilisation systems, including mating behaviour
  (but some species may try and mate with other species - even produce fertile offspring - despite being different species)

Question 14

what is the genetic species model?

Answer 14

• based on DNA evidence

Question 15

what is the evolutionary species model?

Answer 15

• based on shared evolutionary relationships between species
• members of species have a shared evolution and are evolving together
  (but not always easy to apply - there is not always a clear evolutionary pathway for a particular organism)

Question 16

what does the term molecular phylogeny mean?

Answer 16

it is the analysis of the genetic material of organisms to establish their evolutionary relationships

Question 17

what are the limitations of all the species models?

Answer 17

1. finding the evidence - many species haven’t been observed mating (setting up a breeding programme is time-consuming, expensive)
2. plants of different species can still interbreed and produce fertile offspring, at what point should the offspring be considered a different species?
3. many organisms don’t reproduce sexually. the definitions with reproduction are irrelevant for bacteria/ protoctists/ others that reproduce asexually.
4. fossil organisms can’t reproduce + don’t have accessible DNA, but still need to be classified