Is there a bias in deep sea diversity patterns? Graeme T. Lloyd
CollaboratorsAndrew Jeremy Paul Smith Young Pearson
Talk Outline• Introduction• Deep sea diversity patterns: – Deep sea diversity through time – Deep sea rock record through time – Correlations – Modeling• Species-per-genus patterns: – Species-per-genus through time – Deep sea rock record through time – Authors through time – Correlations – Modeling• Other diversity curves
Fossil record is our only record of the diversification of life
Diversity correlates with rock record on land… Peters and Foote 2001 Smith and McGowan 2007
…but what about the deep sea?• Widely regarded as the best record we have: – Larger spatial extent than land – Abundant and widespread taxa – Near continuous sedimentation – Well studied (e.g. DSDP/ODP/IODP)
The database• Study group is Coccolithophores• Novel compilation from North Atlantic• Compiled from 40 years ODP/DSDP data• >50,000 occs from >15000 samples• High temporal resolution (nanno zones)Questions:• What is the deep sea diversity pattern?• What is the deep sea rock pattern?• Are the two correlated to any degree?
Correlation tests• First both time series were log-transformed• Long term test: – Simple correlation• Short term tests: – First differences (absolute) – Moving average differences (relative to long term trend)• Degree (rho) and significance (p) of correlations determined using Spearman rank
Deep sea conclusionsQuestions:• What is the deep sea diversity pattern? – Linear rise with short-term fluctuations• What is the deep sea rock pattern? – Exponential rise with short-term fluctuations• Are the two correlated to any degree? – Yes, strongly and significantly, long-term and short- term – N sites is a good predictor of species richness
Higher taxa as species proxies• Used since the earliest diversity curves…• …and continue to be (e.g. Alroy et al. 2008)• Originally pragmatic (less data required)• Then argued that species are inadequate• But, adequacy of higher taxa to represent species-level patterns is essentially untested
Flessa and Jablonski 1985 • Only explicit test of species-to-higher taxon ratio • Compared families to number of named species in Zoo. Record (Raup 1976) • Pattern of change differs; families become more speciose
Our database is superior!• Species are standardised (synonyms)• Species are assigned to genera• Species are often widespread• Species are long-ranging• Species are comparatively stable taxonomically• Question: how does the species-to-genus ratio change over time?
Short-term correlationSpecies per genusN sites
Short-term correlationSpecies per genusN authors
Correlations and conclusions• Both number of sites and number of authors significantly correlate with species-per-genus• Which is the best explanatory model? – Akaike weights = a combined model – Variance partitioning = a combined model• Genera are not an accurate proxy for species• Shift in species-per-genus ratio is best explained by a combination of sampling and worker bias, with limited room for a biological explanation