Life on Earth Flashcards
de Vos et al 2014
sixth great extinction
contemporary rates are 1000-10,000 times higher than the background geological record
UN 2019
1/4 of species at risk of extinction
economic importance of biodiversity
In UK, contributes to all sectors of the economy (gov 2024)
Biodiversity definition
“The variability among all living organisms from all sources, inter alia, terrestrial, marine, and other aquatic ecosystems and the ecological diversity within species, between species and of ecosystems” (Article 2, Convention on Biological Diversity, or the Rio Convention, 1992)
measurement of biodiversity
species is just one way to measure
working estimate 3.5mil-111.5mil
Uncertainties from -
Taxonomic groups, viruses, bacteria, fungi, mites, insects
Habitats and biomes, soils, tropical biomes, deep-ocean benthos
On average >15,000 new species discovered each year, most are insects
Insect Biodiversity
2-20 million species, crucial to successful ecosystem functioning (pollination, food source).
Beetles have the largest amount. Panamanian rainforest (Erwin, 1998), Luehea seemannii tree, one tree had 400 different species of beetle out of the canopy, 200 living in lower limbs and trunks.
species definition
Darwin did not define in origin of species (1859)
A distinct reproductive group, a population of organisms which naturally mate in the wild and produce viable offspring, which can continue to reproduce.
inter -species reproduction produces sterile hybrids.
harder to use the concept with plants - false oxlip (primrose and cowslip hybrid)
evolutionary species concept
Organisms which have direct ancestor-descendant relationship, i.e. shared evolutionary history.
Determined from fossils.
Precise evolutionary history of fossils impossible to know.
Phylogenetics
study of evolutionary history of life using genetics
genotypic clusters
genetic advancement of morphology (identifying species based on physical characteristics).
genotypic clusters classify species based on genetic similarity
DNA revolution - can build phylogenetic trees based on data
problems with genotypic clusters
Hybridisation can blur genetic boundaries, creating a continum of genetic variation rather than discrete categories (Mallet, 2008)
species richness
the number of different species represented in an ecological community, landscape or region
diversity within the plant kingdom
can be categorised by growth form - structural and functional traits, size, lifespan, how they grow.
Trees, herbs, epiphyte, climber
species richness vs biodiversity
Biodiversity includes multiple levels of biological variation - genetic, species and ecosystem diversity
considers species eveness
functional diversity (species importance)
ecological resillience
Biogeography history
Joseph banks, went on captain cooks voyage. collected species, enslaved people to do so
Alfred Wallace independently theoreticised evolution by natural selection
naming of species - most birds discovered in GS named to honour people in GN
ecosystem services
benefits they provide to humanity, come from natural capital
concept popularised by millenium ecosystem assessment, 2005
provisioning (food, energy), regulating (carbon sequestration, pest control(, supporting (primary production, nutrient cycle), cultural services
Keystone species
no precise definition, some species have more important effects than others
disproportionate impact in their environment
cultural keystone species
trophic cascade
how predators can structure entire communities through interaction with prey - alternative to view that ecosystems are controlled by nutrient availability
top down and bottom up recognised as operating simultaneously
Lake Guri experiment
1986 Dam on Caroni river, venezuela for HEP
Extensive rainforests reduced to islands, had lost up to 75% of species on smaller islands (largest had retained most)
Within 4 years, all islands had lost their top predators
Shows the principles of the Theory of Island Biogeography, that smaller islands sustain fewer species
Ecological release, fewer species competing for resources
Populations of remaining species increase and become more abundant on smaller islands
As habitat shrinks, predators are lost, leads to trophic cascade effect
Overgrazing
wolves in yellowstone NP
Wolves were seen as problematic
Extapation (locally extinct) in mid-1920’s
Their pray, the elk, grew in population
They browse on trees etc., vegetation cover declined
Reintroduced wolves, decline in elks, recovered vegetation (1996)
other factors or trophic cascade? - compare age of different trees in NP, none older than 1996, recovery of alders associated with reintro.
direct (reducing numbers) or indirect (behavioural)
Grassland - lack of wolves increases productivity, herbivory stimulates root growth.
biodiversity and ecosystem services
some evidence that BD is correlated with regulation of ES
lack data
NPP
NPP = GPP - respiration
(GPP = total energy fixed by photosynthesis).
seasonal varitation.
oceans and land are similar - land is disproportionatley more important in terms of area.
biome
- a world region compromising communities of plants and animals characterised by their adaptations to that particular climate and/or environment.
photosynthesis
temp - rate increases until around 18 C, levels off
role of precipitation increases NPP irrespective of biome, once saturated NPP is unchanged
latitudinal gradients of biodiversity
mammal, bird, amphibian are not congruent.
species are richer at lower latitudes.
not tropics, around 20 degrees is most richness
Equilibrium explanations
iodiversity differences are a product of modern biological and ecological processes (holocene). Area - tropics have the greatest landmass, Temperature is fairly constant, complex topography and community of vegetation.
Greater habitat diversity correlates with greater resource gradients and niche space. Stratified structures, canopies.
Environmental stability, annual and geological scale.
This relationship breaks down at smaller scales. Estuaries, marshes etc have very low diversities but high NPP, often dominated by a single species of plants
historical (non-equilibrium) explanations
- geological legacy, Tropics have not been through repeated quaternary glaciations as the higher latitudes have. Local species in higher lats will have either gone locally extinct or migrated towards tropics.
hotspots
A hotspot should already have lost 70% of its primary vegetation.
Notion is contested, politics plays a role. Only considers species richness.
endemism
requirements for life
energy source, solvent, right conditions (temp, ph, raw mats)
ecological tolerance
An organism can survive across a range of environmental conditions, ‘niche breadth’, but does the best in optimal conditions.
Liebig (1840)
law of the minimum. productivity , growth or reproduction of an organism will be constrained if one or more factors fall below its limiting level.
niche
- determined by habitat in which a species lives
-relationship of that species to its environment and other species - related to resources
A species exists in multidimensional space defined by the different physical factors affecting its abundance
light and photosynthesis
approx hyperbolic response to light. Low intensity, linear increase in rate.
Compression point - point at which light intensity and photosynthesis are sufficient to offset loss of energy through respiration
too much light - photo-inhibition, shrinking of chloroplasts
fundamental niche
entire set of optimum conditions which a species can occupy in the absence of competition (potential niche)
realised niche
actual set of conditions in which a species normally lives
competitve exclusion
complete competitors cannot coexist indefinitely (Grinnel, 1904)
If they are competing for the same resources, then one will overcome the other, leading to extinction, or evolutionary shift towards a different ecological niche
coexisting species must have different niches
cambridge
high species richness - habitat variety, lands under arable cultivation, river cam, built areas, intensity of recording
undervaluation of urban ecology
vegetation succession
implies progressive sequence through time/space
one of earliest ecological concepts (Clements, 1916,28,36)
not applicable to range of env. (Dominance of NA/european landscapes)
temperate communities e.g, water is needed in mediterranean
passive rewilding
Broughton et al., 2021 - Rewilding – “restoration of self-regulating and dynamic ecosystems free from direct human interference”
rewilding experiment at Mondks Wood national nature reserve
Remote sensing to look at woodland cover
To what extent is it evenly distributed or patchy
Spatial autocorrelation - establishes the likelihood that a tree is present because there is another growing nearby
All tree species showed significant clustering (high spatial autocorrelation)
Why?
Seed dispersal- wind (anemochory), animal (zoochory) - Eurasian Jay - collects and buries acorns in autumn, find them in winter, hide more than they find, will then germinate and grow
cambrian explosion
30Ma pulse in evolutionary activity, expansion in species
burgess shale - best record we have of cambrian animal fossils
permian mass extinction
96% of all species went extinct
life on earth evolved from the 4%, it is belived that within the 4%, 86% of genetic material was encapsulated.
provide opportunities - diversification, reshuffling, reorganisation of ecosystems. can take millions of years for a new equilibrium to become established
uniformitariansim
natural processes behave more or less in the same way today as they have throughout the past, and will continue to do so in the future - Hutton 1795
loss of megafauna
pleistocene overkill (Martin & Wright, 1967) - longterm steady decline in megaherbivores beginning 4-5 million years ago, long beofre humans were capable of exerting top-down control on large mammals
svenning et al (2024) - little support for any major influence of climate …”, and “there is strong and increasing support for human pressures as the key driver of these extinctions”, “but the topic remains controversial”
megafaunal extinctions impacts
trophic structure - shorter food chains, simpler ecosystems, abundance and behaviour of grazing animlas
ecosytem biochemisty - biogeochemical cycling fo nutrients. nutrients locked slowly into decomposing matter, nutrient poor systems
allopatric speciation
biological populations become geographically isolated to an extent that prevents or interferes with gene flow.
movement of continents, formation of mouuntains, islands - human activity
genetic drift, different mutatuons in seperate populations gene pools.
Mayr 1942.
founder effect
loss of genetic variation when a new population is established by a small number of individuals from a larger population
mayr - 1942
new pop may be both geonotypically and phenotypically different from parent population
