What is a species? Flashcards
What is a species?
Doesn’t have one single definition = long standing problem
- Concept is one of the oldest + most fundamental in biology but still no satisfactory definition- Dobzhansky (1935)
Why do species matter?
- Underpins understanding of natural systems- hierarchy of life needs a definition
- Biogeographical patterns forming across the world and how they form
Why does counting species matter?
mass extinction- by counting number of species we can determine what has been lost
Why is defining a species important?
Majority of species not well described
species inflation- elevated sub-species
What is species inflation caused by?
Political endemics- countries compete for highest number of endemic species
Conservation and careerism- new species in area make it more attractive + easier to get money
Name one of the 1st people to try and officially define a species
Ernst Mayr
Name the 5 different concepts used to define a species
Nominalistic
Morphological
Biological
Genetic
Phylogenetic
How may definitions of a species since Ernst Mayr are in use?
27 but keeps changing
Describe the contribution of Hey (2006) in defining a species
evaluated varying definitions and incorporated
various things e.g. morphology, genetics, sterile off-spring
Concluded that all species share the fact that they have arisen from evolutionary processes
What does this graph show?
Graph shows global primate species richness overtime- highlights species inflation:
- Increase in number of primate species is not due to discovery of new species but reflects changing ways people have tried to define a species
- These species were always there but were just defined differently
Describe an example of a new species being discovered
2017 = announced new species of orangutan- now 3 species instead of 2
Happened because they found a population of orangutans that were isolated and had slightly different characteristics e.g. denser fur, different teeth + genetically distinct from other 2 species
Scientists were aware they were there but the testing had never been done to be able to define them as a different species
As well as orangutans, describe another example of a new species being discovered
Genetic analyses of giraffes and found that there were 4 different species instead of 1 that was subdivided into 11
The reason this was done = conservationists wanted to ensure when relocating giraffes they wanted to maintain genetic diversity within species
Very distinct species which do not normally interbreed
Describe the nominalistic approach to defining a species
= philosophical view that only individuals exist in nature and species are artificial constructs of human minds
Species are entirely human constructs from basic human instincts- no biological relevance
What are the arguments for the nominalistic approach?
+ Different cultures vary in their classifications- able to understand different uses of species
+ Western taxonomy is not consistently seen
+ Number of types documented reflects interest or usefulness
What are the arguments against the nominalistic approach?
- Differences among species often correlated- e.g. morphological, reproductive, genetic traits- evolutionary processes confused by this system as well as genetically inherited traits not linked with phenotype
- Those traits reflect evolutionary past
Describe the morphological approach to defining a species
Things that look different are considered a species
Basis of traditional taxonomy (based on physical traits) but no theoretical foundation instead just looking at shapes of things and cross referencing it with a list of shapes of things identified by someone else in the past
What are the arguments for the morphological approach?
+ Physical traits map onto behaviour and evolution
+ Can be made quantitative e.g. MOBAT = morphology based alpha taxonomy
+ Type specimens used for comparisons
What are the arguments against the morphological approach?
- Designations vary among taxonomists (lumpers vs splitters)- inconsistent taxonomic keys
- Depends on feature selected
- Omits reproduction, genetics and evolution
- Excludes important non-visual characters (e.g. olfactory (smell), acoustic, behavioural)
Describe the biological approach to defining a species
groups of actually or potentially inbreeding natural populations that produce fertile offspring
Reproductively isolated from other groups
Requires detailed knowledge of each species
What are the arguments for the biological approach?
+ Reproductive isolation leads to genetic and morphological change
+ Many species cannot interbreed (or form sterile offspring)
What are the arguments against the biological approach?
- Hybridisation common in many groups of animals- US Red wolf- speculated to be ancient hybridisation of grey wolf + coyote
- Ring species = connected series of neighbouring populations that can interbreed but at the ends of the ring the populations don’t interbreed
- Impossible to test effectively for all species- cant get all organisms to breed to test whether they produce fertile offspring
Describe the phylogenetic approach to defining a species
combines morphological approach with evolutionary history of an organism = populations differing by at least one taxonomic character (= particular attribute of an organism)
Common ancestry (no hybrids), aka monophyly- all descendants have one common ancestor
Ignores reproductive isolation but differ in some aspect of their morphology = different species
What are the arguments for the phylogenetic approach?
+ Reflects evolutionary history
+ Identifies divergent populations = accumulation of differences between closely related populations within a species
What are the arguments against the phylogenetic approach?
- Often increases number of species by 50% = species inflation
- May be picking up trivial differences- no adaptive significance e.g. different dog breeds
- Driver of species inflation: many controversial species
- Usually elevates existing sub-species or populations rather than discovering entirely new organisms
Describe the genetic approach to defining a species
uses DNA analysis techniques to separate species with no other info required- useful as statistical analysis and data processing techniques can be used to reduce subjectivity
Do not need to know anything morphological about sample being tested
Increasingly rapid due to PCA = principle component analysis
What are the arguments for the genetic approach?
+ Bar-coding allows ID by non-specialists
+ Works well for sympatric groups- ones that exist in the same location
+ Identifies cryptic species = species that look the same but are genetically distinct
+ Valuable for group with no obvious visual differences e.g. fungi, mosquitoes
What are the arguments against the genetic approach?
- No fixed boundary between species is possible
- Consistent rules are not applied
- Genetic exchange does occur among species = obscures boundaries
- Works poorly for allopatric groups- ones that exist in different locations due to genetic drift = change in gene pool of a small population due to random chance
If a species cannot be defined, what is it?
Hypotheses- moving targets that have to be frequently updated as new tools are improved or invented
What is an ESU?
= evolutionary significant units = populations of organisms that could be defined as the same species but are distinct for purposes of conservation
What does biodiversity + species richness correlate with?
- Higher taxonomic levels
- Traits and characters
- Functional diversity
What does species richness and biodiversity not reflect?
- Genetic diversity
- Phylogenetic diversity- could be more useful than species richness
- Representative plant species
Describe Linneas’ nomenclature system
= system of naming organisms by 2 words = species + genus
How many species did Linneas identify?
9000- mostly temperate with a biased composition- we know now this is not correct
Describe some more recent attempts to classify species
Stork (1993)- estimated 1.8 million species with expert assessments and a compilation of sources
Catalogue of life = 92% coverage of taxa- 2018 = 1,754,878 species
- 61,579 extinct
- 84% undescribed
- 14th September 2023= 2,119,462 species
Name 4 ways to estimate number of species
- extrapolation of data
- Scaling body sizes
- Scaling taxonomy
- sample based estimates
What does this paper show about discovery rates?
Projections were modelled of species estimates based on current rates of discovery of different groups
Some groups of organisms are better described than others- discovery rate in birds and mammals flattens whereas other groups have a greater trajectory – so more species to define
How many species are estimated after extrapolation of data?
6-7 mil
Describe some problems with extrapolating data when estimating number of species
- Assumes similar patterns
- Poor when few known
- Inconsistent species concepts post 1984
- Tropics under sampled
- Incorrect taxonomy
- PCR (=polymerase chain reaction) allows DNA sequencing- discovery rates increased after PCR was invented which causes disruption when extrapolating data
Describe an example of extrapolation of data
e.g. Raven-1985- looked at difference in species richness in tropics vs temperate regions
RESULTS:
- 2:1 tropics: temperate- more known about species here as western scientists live here
- 2/3 described insects are temperate
- 3-5mil total insects after extrapolation
Are species names valid?
US fossil mammals- many of these were named wrong
- Well studied group
- Not species rich
- Many synonyms = misnamed taxa
But- lag in revision as there are many new species and studies show it is only revised every 10-100 years
Name another way to estimate number of species
Scaling- body sizes
Descibe the method of scaling body sizes
sort of method of extrapolation but biological characteristic is used that is common to certain groups to predict changes in numbers
What is this graph showing (May 1988)?
approximately linear relationship between body size and number of species
= smaller the body size the more species there are = negative relationship
Evaluate the use of scaling body sizes to estimate number of species
- More small species
- 10 x length = 10³ volume of organism – 100 x species
- Breaks down below 1cm- When very small body size (below 1cm) the relationship breaks down
- Very vague method
- Assume only true to 0.2cm
How many species are there estimated to be when following the scaling body sizes method?
10mil species globally
What is another thing that can be scaled to estimate number of species?
Taxonomy
Describe what these graphs are showing
e.g. Phylum levels off (at the asymptote) showing all phyla have been discovered- makes sense as broad category
e.g. species level is nowhere near the asymptote = shows have not discovered them all
7th graph- combined all patterns which shows if move up taxonomic level = clear relationship between number of species expected at each level
What is an asymtote?
When line levels off on a graph = maximum capacity
How many species were estimated when scaling taxonomy?
8.7 billion
Describe the method used in this paper
12 year old paper that is highly regarded = another form of scaling using taxonomy:
Looked at number of taxa known at each taxonomic rank e.g. genera, class etc- estimated an asymptote = when line levels off
Describe an example of sample based estimates
Erwin (1982) in Panama =
Wanted to estimate number of TRF insects:
1. Used intensive campaign of sampling in rainforest using Canopy fogging
2. tents are put below trees to catch the dead stuff
RESULTS = Fogged 19 trees and found more that 1100 species
Define: Canopy fogging
= process of applying insecticide to foliage of trees and shrubs
What is the Coleopterists bulletin?
refereed quarterly journal which includes a wide variety of articles on taxonomy and ecology of beetles (= Coleoptera)
What was done with Erwins findings and what were the results?
Data was extrapolated:
RESULTS =
- 40% arthropods are beetles
- There is 2 x the species richness in the canopy vs floor
- 50,000 species of Tropical trees can calculate and come to estimate that there are- 30mil tropical rainforest arthropods, 100mil species globally
What is a cryptic species?
biological groups that look identical but cannot interbreed
Describe a study on cryptic species
Hebert et al (2004):
= 10 caterpillars that are all different species- however the adult emerging from caterpillars looks exactly the same
- Scientists believed they were different morphs of same species
- Discovered to be a cryptic species after genetic analysis and studies on host plants
What are estimates based on and why is this?
animals as most common and similar to humans = more likely to study
- > 70% named species = animals
How many bacteria are estimated to have been named and why is this?
5% of bacteria- bacteria evolve so rapidly that estimate is most likely out of date
How many plants are said to have been named?
400,000
Describe what the method of this study
Best estimate
Method = give overview of different ways people estimate species richness- shows how varied these methods could be
- Leave out certain groups to highlight how varied methods can be e.g. bacteria included value of species richness = 1 trillion
