species-energy relationships in the deep sea (marine lecture 3) Flashcards
Why are there ecogeographic gradients in diversity?
- biodiversity not evenly distributed worldwide
- why?
- hypotheses: climate, age, area, geometry
- availability of environmental energy may be key
What is the relationship between energy, productivity and diversity?
- productivity-diversity relationships
- productivity determines food availability
- higher productivity should therefore support more species
- but diversity may decrease at highest productivities
What is the relationship between energy, productivity and diversity?
- species-energy theory
- aka “more individuals hypothesis”
- higher productivity increases abundances of individual species
- therefore higher productivity increases likelihood of rare species reaching viable population sizes
- may also increase population growth/ speed post disturbance recovery rate
- at highest productivities may lead to competitive dominance, decreasing diversity
What is the relationship between energy, productivity and diversity?
- resource ratio theory
- if productivity isn’t limiting, something else is
- different species dominate either end of productivity spectrum
- coexistence and diversity highest at intermediate productivities
What is the relationship between energy, productivity and diversity?
- more specialisation theory
- resources too rare at low productivities to support specialisation
- more energy, more opportunities for specialists to escape competitive exclusion
- more productivity therefore = more diversity
What is the relationship between energy, productivity and diversity?
- one more trophic level
- higher productivity allows for greater food chain length
- increases predator diversity
- higher predator diversity can prevent competitive exclusion at lower trophic levels
- higher productivity = higher diversity
What is the relationship between energy, productivity and diversity?
- competitive exclusion
- competition increases in high productivities
- dominant species exclude inferior competitors
- higher productivity = lower diversity
What are the challenges explaining relationships between energy, productivity and diversity?
- several hypotheses make similar descriptions
- what is the scale? taxonomic/spatial/temporal
- what do we mean by diversity? energy?
What do we mean by energy?
- how is this measured on land
- problem with terrestrial studies
- energy available to life
- on land quantified by productivity, measured by NDVI
- terrestrial studies problem is that productivity is always highly correlated with other factors proposed to explain diversity e.g. temperature/ precipitation
How can deep sea studies be test-beds for species-energy theory?
- basically 0 in situ productivity
- quantify productivity as C flux (food availability)
- productivity decoupled from temperature as is cold everywhere in deep sea
- chemical/thermal energy potentially isolated from each other
What are species-energy relationships in deep-sea molluscs?
- strong unimodal relationship b/w energy and diversity in deep-sea gastropods and bivalves
- relationship much stronger than between diversity w temperature or depth
- chemical energy drives mollusc diversity from continental shelf onto abyssal plain
Is energy always more important than temperature?
- temperature drives organismal processes (e.g. metabolic rate), no evidence that chemical energy does
- variation in c flux instead drives patterns of biomass, abundance and diversity
- temperature more important on continental shelf/upper slopes
- C flux more important in deep sea
How do wood falls provide a deep sea energy source?
- wood transported in great quantities from rivers to ocean
- saturates and sinks
- energetically isolated food source in deep sea
- rapidly colonise by a range of organisms, mostly wood fall specialists entirely dependent on wood for energy
How can experimental wood falls be used to test species-energy relationships in deep sea? Do they support them?
- wood of varying size placed in deep sea
- discrete habitat boundaries
- whole communities collected and analysed for easy quantification of diversity on wood with different amount of energy (size)
- individuals increase with resource (wood) size
- so do species
- richness is a function of abundance, supporting species-energy hypothesis
- some evidence for rarer species on larger logs
- more specialisation, narrower niches