Lecture 3 - Biodiversity Flashcards
What is biodiversity?
- The variety of life.
- Is a continuum, but we subdivide it:
1. Genetic diversity: underlies behavioural & morphological (phenotype) diversity e.g. population of fish vary in colour (likely genetic)
2. Species diversity: the variety of species that compromise a biological community (group of interacting organisms)
3. Community & ecosystem diversity: the different biological communities & their associated ecosystems.
Genetic Diversity
- The total number of genetic characteristics in the genetic makeup of a species.
- e.g. Mountain goats, some variation within a population but also variation between different populations e.g. on different mountains variation in the frequency of different coat colours.
- 2 copies of each chromosome, one from each parent, genes located in different areas of chromosome, may have 2 copies the same or different for each gene. E.g. have B1 gene from both parents = homozygous for B gene, but 2 different copies of the A gene (different alleles) = heterozygous for A gene.
- Genetic variation is raw material for evolutionary processes.
- DNA mutations are represented by different alleles & depending on where the differences are, those alleles could lead to different proteins & different proteins can produce different phenotypes (including behaviour)(usually behaviour is effected by many different genes).
Measuring Genetic Diversity
- Because of the importance of genes in evolution a goal of conservation is to maintain genetic diversity, providing resilience and enabling adaptation.
- E.g. if a new disease comes into a population, if all individuals are genetically identical then they vulnerable to disease wiping them out. If there’s genetic variation there then some may have genes for resistance.
- E.g. sample 5 frogs from a population in a pond and sample the genotype at 2 loci. Gene A influences size (2 alleles) and Gene B influences colour (3 alleles). This allows to calculate: 1) heterozygosity and 2) polymorphism (more than one allele) & allele frequencies. This can tell us if heterozygosity is low which might indicate there is a lot of inbreeding or not enough individuals in the population to maintain genetic diversity.
Species Diversity: Different meanings of species
- Biological concept of species: different species do not breed with eachother.
- Morphological species concept: a group of individuals that is morphologically, physiologically or biochemically distinct.
- Evolutionary species concept: a group of individuals that share unique similarities of their DNA.
Difficulties with the definitions of species diversity
- e.g. The western meadowlark and the eastern meadowlark are distinct species as they have different songs and do not interbreed but they look very similar. Therefore the morphological species concept is flawed in this example.
- e.g. The hybrid tiger salamander is larger than its parent species, the California tiger salamander.
How many species are there?
- 1.24 million eukaryotic species been described.
- 1.05 million on land and 0.19 million in oceans.
- 0.75 million are invertebrates (including 0.35 million beetles)
Biases exist:
- towards large, abundant, widespread, temperate, terrestrial species.
- many ‘new to science’ species been long know by locals.
- small, cryptic (a species which looks very similar to another, but is reproductively isolated from it) species are underrepresented, especially prokaryotes (because they reproduce a-sexually its hard to differentiate species).
~ 16,000 new species being described every year
Measuring Species Diversity
- species richness (how many species there are) and species evenness (whether they are evenly spread)
- populations can have the same number of species but different evenness.
Note: in Simpsons diversity index, high number = low diversity, in contrast to other measures such as Shannons diversity index.
Taxonomic Diversity
- often try focus on species when looking at diversity might not have data at species level
- sometimes useful to look at other levels of taxonomic diversity e.g. genus or family level
Community and Ecological Diversity: Conservationists try to preserve: Trophic pyramids/structure
- describes amount of energy & biomass found at each trophic level.
- Producers at bottom (energy from sun), primary consumers, secondary consumers (predators, eating primary consumers).
- Energy is ‘lost’ at each level (through heat loss & not all digested).
- if don’t protect that can have trophic cascades occurring: the loss of a single species can result in extinctions of multiple species.
- e.g. have kelp forests (primary producers), & sea urchins (herbivore) which feed on the kelp, the carnivore (sea otter) feeds on the sea urchins. But if loose sea otters the herbivores get out of control and ate lots of the kelp forests, so lost kelp which many other species depend on.
- e.g. reintroducing wolves to Yellowstone park. Wolves were hunted out, a trophic cascade happened, ended up with over abundance of deer & other species, that overgrazed the land. When wolves reintroduced, kept population of deer in check but also changed the deers behaviour. They have a ‘landscape of fear’, where the prey animals are aware of where they are most at risk from being hunted so go into those areas less & don’t graze as much in those areas, so regeneration of woodland, that impacts rest of ecosystem e.g. slowing down river movement & protection against floods.
- A linked concept is Functional diversity: the variety of ecological functions that species perform in ecosystems. (Think of function the species performs in ecosystem, if loose multiple species with same function might completely loose the function)
Community and Ecological Diversity: Conservationists try to preserve: Food web complexity
Different measurements can be made from food webs:
1. Linkage density (D): average number of interactions between species.
2. Connectance (C): the proportion of all possible links between species that are realised.
E.g. marine food web, number of species (S) = 92, Number of links (L) = 997
Linkage density (D) = L/S = 11 (each species on average connected to 11 others)
Connectance (C) = L/S^2 = 0.12 (12% of the potential links that could be there are there, not gonna get 100% as top predator is not gonna eat algae for example)
- to conserve species, also need to conserve those they rely on
- few links = more vulnerable (less resilient)
Community and Ecological Diversity: Conservationists try to preserve: Species composition
- some species particularly important to their community/ ecosystem
1. e.g. ecosystem engineers: species that form habitats for others to use e.g. beavers (creates dams)
2. e.g. keystone species: have a high impact on other species through their interactions with other species. - E.g. Ochre sea stars eat mussels, they predate on most abundant, fast reproducing mussels so have greater variety of molluscs. If remove sea stars number of species overall declines.
- argument that conservation efforts should focus on species with high impact on the community so ecological cascades do not happen. (Keystone species has low abundance but high level of impact on rest of community).
Global patterns and drivers of biodiversity: the rise (and occasional falls) of biodiversity
- diversity has steadily increased over time
- some occasions of mega extinctions
Different in different regions of the world:
1. Biogeographic realms: large regions across the globe where organisms share common geologic and evolutionary histories.
- 8 identified (related to tectonic plates)
- composed of biomes: areas that can be identified by their dominant vegetation type (on land) e.g. tropical rainforest, deserts
- In the aquatic habitats identified by dominant physical processes.
2. Further divided into ecoregions: units of land containing a distinct assemblage of natural communities and species. E.g. WWF divided terrestrial biomes into 867 ecoregions, used to recognise areas for conservation.
The most diverse biomes
- tropical forests: occupy 7% land area, contain > 50% the worlds species.
- coral reefs: occupy <0.1% of ocean surface area, but home to > 25% of all marine species
- large tropical lakes and river systems: make up <0.01% of worlds water and ~ 0.8% of earths surface. Support ~125,000 species.
- Mediterranean communities - moist winters, hot dry summers = high plant diversity. Occur in Mediterranean basin, southwestern Australia, California, central Chile, & the South African cape (which has 9000 endemic (present just in that area) plant species)
Biodiversity hotspots have been identified
- 25 hotspots (terrestrial): 44% of all species of vascular plants, 35% of all vertebrate species but just 1.4% of earths land surface.
Biodiversity is higher in tropical regions
- across marine, terrestrial, and freshwater habitats
- been persistent over time (looking at fossil records)
Why?
- biodiversity evolves through mutation, migration, natural selection and genetic drift, which results in patterns of speciation and extinction.
These processes don’t occur evenly, tropics generally have:
- greater area: species diversity increases predictably with area (larger popualtion sizes, lower extinction rates)
- greater productivity: more sun and rain lead to greater plant productivity and more herbivores and carnivores (more niches)
- more time: equatorial regions have had stabler climate (e.g. no glaciation)
