Biodiversity Trends Within the Holocene John Birks, Vivian Felde, and Alistair Seddon University of Bergen.

Biodiversity Trends Within the Holocene

John Birks, Vivian Felde, and Alistair Seddon

University of Bergen

‘Anthropocene’ has suddenly become a buzzword in ecology and biogeography in the last few years, despite no clear definition for its lower boundaryRecent publications on temporal trends of different units or interest in biodiversity across in the ‘Anthropocene’ Alien speciesConservationCoral growthTemporal ecologyForestry

Defaunation

Plant biodiversity

Island biogeography

Archaeogenomics & ancient DNA

Observational tech-niques for biodiversityBiological controlBiodiversity changesSpeciation

‘Anthropocene’ now well established in vocabulary and research agenda of ecologists, conservationists, and biogeographers even though there is no agreed definition. Band-wagon effect!

McGill et al. (2015) identify four spatial scales and four measures of biodiversity and two trends

Type of diversity  Alpha (α) diversity

The number of taxa present in an assemblage

α-diversity trend

Changes in α-diversity through time

Spatial beta (β) diversity

Changes in assemblage composition across space (e.g. comparing dissimilarity between the composition of several assemblages for one time period)

Spatial β-diversity trend

Changes in spatial β-diversity through time (e.g. decreases through time leading to biotic homogenisation (Sax and Gaines, 2003))

Temporal β-diversity or turnover

Changes in assemblage composition through time, usually quantified as the dissimilarity between each time step.

Biomass A robust measure of abundance that is often correlated with various ecosystem functions

Spatial scale

Global The entire planet within which extinction and speciation are the dominant processes

Meta-community

A scale that includes spatial heterogeneity and within which dispersal is the dominant ecological process

Local A scale that is dominated by interactions between taxa and by environmental constraintsAlso define a fourth spatial scale of organisation

“biogeographical – a scale within which speciation and global extinctions are the dominant processes (Rosenweig 1995)”

Do not see how this differs from global spatial scale or how to make it operational.

Prefer the simple Sax and Gaines (2003) three spatial scales – global, regional, and local.

McGill et al. (2015)

Four spatial scales, four aspects of biodiversity, 15 trends hypothetical trend evidence-based trend ? little or no evidence

Suggest at meta-community (regional) scale increase in α-diversity and decrease in N or biomass, and at local scale hypothetical increase in temporal -diversity and biomass

In McGill et al. (2015) and the other 13 papers on biodiversity and ecology in the ‘Anthropocene’ no mention of

1. The onset of the ‘Anthropocene’ - ?50, 100, 200, 500, 2000, or even the last 5000–7000 years (‘early Anthropocene’)

2. Biodiversity in the preceding Holocene

Obvious questions that follow McGill et al. (2015) are

• What were the biodiversity trends in the Holocene?

• Are the ‘Anthropocene’ trends a continuation of trends in the Holocene and are they contingent on these trends or are they unique relative to Holocene trends?

Holocene Biodiversity Trends

1. Global scale – few data except for mammals, birds, and marine mega-fauna. Mainly human-induced extinctions

2. Meta-community (‘regional’) scale – pollen assemblages from lakes and bogs provide inferences about floristic and landscape richness and diversity

3. Local scale – less data available from local-scale pollen assemblages. Little change in biodiversity trends

Modern pollen richness (Hill N0) and diversity (Hill N1, N2) are, in part, a function of contemporary floristic richness and diversity (-diversity) (Felde et al. 2015)

and of landscape mosaic structure (Matthias et al. 2015)

Alpha-diversity – rarefaction (analytical or repeated resampling) to estimate N0, N1, and N2

Compositional turnover (temporal -diversity) – rate-of-change or turnover metric (Birks 2007)

Spatial -diversity – diversity partitioning or spatio-temporal analysis of pollen assemblages (Blarquez et al. 2014)

Biomass – pollen-accumulation rates in ‘well-behaved’ simple lakes approximate catchment biomass (Seppä et al. 2009)

Using 120+ pollen diagrams from Fennoscandia, Britain, and Ireland, can derive generalised trends for these four biodiversity components. However, Holocene is not ecologically uniform, so we have produced biodiversity trends for four phases (Iversen 1958; Birks 1986)Protocratic – early-Holocene forest development

Mesocratic – mid-Holocene forest maximum

Homo sapiens – human impact

Oligocratic – acid heath and bog phase

Protocratic – diversity , biomass Mesocratic – diversity –, biomass –Homo sapiens – diversity , biomass Oligocratic – diversity , biomass Last 200 years ‘Anthropocene’ – little change

Birks et al. (2015)

In last 200 years in Homo sapiens phase sites, small decrease in - and spatial -diversity and biomass, and small increase in temporal -diversity

Oligocratic sites show little change in - and temporal -diversity, small decrease in spatial -diversity, and slight rise in biomass (?N deposition)

Meta-community ‘regional’ scale

Differences between palaeodata and McGill et al. (2015) for trends in -diversity

Palaeodata

Homo sapiens

Oligocratic McGill et al.

-diversity –

Spatial -diversity (very small)

Temporal -diversity

– ?

Biomass (very small)

See that at this regional scale, and sites on fertile soils in NW Europe, changes in last 200 years are not a simple continuation of trends initiated in the Homo sapiens phase.

At oligocratic acid sites, recent trends in - and -diversity are primarily a continuation of trends started in the oligocratic phase, with the exception of small decrease in spatial -diversity (‘biotic homogenisation’) and small increase in biomass.

Do not expect same biodiversity trends in the Holocene in, for example, central Europe, Alps, Mediterranean, the tropics, or North America – different modern biota and environments, Holocene biotic and vegetational histories, and environmental and ecological changes.Potentially interesting to explore Holocene and ‘Anthropocene’ trends in biodiversity in aquatic systems-diversity Hill’s N0 (rarefaction or repeated

resampling without replacement to a constant base-sum), N1, and N2

Temporal -diversity PCA, DCA, DCCA, principal curves, rate-of-change analysis

Spatial -diversity ? Not relevant in the limnological context

Biomass Biovolumes and accumulation rates

Biodiversity trends in the Holocene and ‘Anthropocene’ relevant to discussions about planetary boundaries especially the Dearing et al. (2014) ‘safe’ and ‘just-operating’ spaces or boundaries for regional socio-ecological systems. Palaeoecological data can provide an evidence-base for defining environmental limits to ensure sustainability and human well-being at the regional or local scale.

Encourage the increasing number of ecologists and biogeographers writing about ‘Anthropocene’ biodiversity to extend their time-scales to include trends in the Quaternary (Q-time). Biodiversity trends simply did not begin in the ‘Anthropocene’.

Acknowledgements

Hilary Birks

Anne Bjune

Thomas Giesecke

Cathy Jenks

Triin Reitalu

Willy Tinner