title: Holocene shifts in the assembly of plant and animal communities implicate human impacts.
abstract: Understanding how ecological communities are organized and how they change through time is critical to predicting the effects of climate change. Recent work documenting the co-occurrence structure of modern communities found that most significant species pairs co-occur less frequently than would be expected by chance. However, little is known about how co-occurrence structure changes through time. Here we evaluate changes in plant and animal community organization over geological time by quantifying the co-occurrence structure of 359,896 unique taxon pairs in 80 assemblages spanning the past 300 million years. Co-occurrences of most taxon pairs were statistically random, but a significant fraction were spatially aggregated or segregated. Aggregated pairs dominated from the Carboniferous period (307 million years ago) to the early Holocene epoch (11,700 years before present), when there was a pronounced shift to more segregated pairs, a trend that continues in modern assemblages. The shift began during the Holocene and coincided with increasing human population size and the spread of agriculture in North America. Before the shift, an average of 64% of significant pairs were aggregated; after the shift, the average dropped to 37%. The organization of modern and late Holocene plant and animal assemblages differs fundamentally from that of assemblages over the past 300 million years that predate the large-scale impacts of humans. Our results suggest that the rules governing the assembly of communities have recently been changed by human activity.
authors.affiliation: Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington DC 20013, USA.
authors.forename: S Kathleen
authors.initials: SK
authors.lastname: Lyons
authors.affiliation: Department of Environmental Science and Biology, The College at Brockport - SUNY, Brockport, New York 14420, USA.
authors.forename: Kathryn L
authors.initials: KL
authors.lastname: Amatangelo
authors.affiliation: Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington DC 20013, USA.
authors.forename: Anna K
authors.initials: AK
authors.lastname: Behrensmeyer
authors.affiliation: Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington DC 20013, USA.
authors.forename: Antoine
authors.initials: A
authors.lastname: Bercovici
authors.affiliation: School of Natural Sciences, University of California, Merced, 5200 North Lake Road, Merced, California 95343, USA.
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Blois
authors.affiliation: Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington DC 20013, USA.|Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: Matt
authors.initials: M
authors.lastname: Davis
authors.affiliation: Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington DC 20013, USA.
authors.forename: William A
authors.initials: WA
authors.lastname: DiMichele
authors.affiliation: Hominid Paleobiology Doctoral Program, Center for the Advanced Study of Hominid Paleobiology, Department of Anthropology, George Washington University, Washington DC 20052, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Du
authors.affiliation: Department of Geosciences and Geography, University of Helsinki, PO Box 64, 00014 University of Helsinki, Finland.
authors.forename: Jussi T
authors.initials: JT
authors.lastname: Eronen
authors.affiliation: School of Social Science, The University of Queensland, Brisbane, Queensland 4072, Australia.
authors.forename: J Tyler
authors.initials: JT
authors.lastname: Faith
authors.affiliation: Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington DC 20013, USA.|Center for Macroecology, Evolution and Climate, University of Copenhagen, Copenhagen 2100, Denmark.
authors.forename: Gary R
authors.initials: GR
authors.lastname: Graves
authors.affiliation: Biological Sciences Graduate Program, University of Maryland, College Park, Maryland 20742, USA.|Florida Museum of Natural History, University of Florida, Gainsville, Florida 32611, USA.
authors.forename: Nathan
authors.initials: N
authors.lastname: Jud
authors.affiliation: Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington DC 20013, USA.|Department of Entomology, University of Maryland College Park, College Park, Maryland 20742, USA.|Key Lab of Insect Evolution and Environmental Changes, Capital Normal University, Beijing 100048, China.
authors.forename: Conrad
authors.initials: C
authors.lastname: Labandeira
authors.affiliation: Department of Integrative Biology and Museum of Paleontology, University of California Berkeley, Berkeley, California 94720, USA.
authors.forename: Cindy V
authors.initials: CV
authors.lastname: Looy
authors.affiliation: School Biology and Ecology &Sustainability Solutions Initiative, University of Maine, Orono, Maine 04469, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: McGill
authors.affiliation: Department of Geology, University of Cincinnati, Cincinnati, Ohio 45221, USA.
authors.forename: Joshua H
authors.initials: JH
authors.lastname: Miller
authors.affiliation: Hominid Paleobiology Doctoral Program, Center for the Advanced Study of Hominid Paleobiology, Department of Anthropology, George Washington University, Washington DC 20052, USA.
authors.forename: David
authors.initials: D
authors.lastname: Patterson
authors.affiliation: Department of Biological Sciences, Macquarie University, Sydney, New South Wales 2109, Australia.
authors.forename: Silvia
authors.initials: S
authors.lastname: Pineda-Munoz
authors.affiliation: Department of Anthropology, Human Origins Program, National Museum of Natural History, Smithsonian Institution, Washington DC 20013, USA.
authors.forename: Richard
authors.initials: R
authors.lastname: Potts
authors.affiliation: School of Life Sciences, University of Nevada-Las Vegas, Las Vegas, Nevada 89154, USA.
authors.forename: Brett
authors.initials: B
authors.lastname: Riddle
authors.affiliation: Department of Integrative Biology, Oregon State University, Corvallis, Oregon 97331, USA.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Terry
authors.affiliation: Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington DC 20013, USA.
authors.forename: Anikó
authors.initials: A
authors.lastname: Tóth
authors.affiliation: Chair of Ecology and Biogeography, Nicolaus Copernicus University, Lwowska 1, 87-100 Torun, Poland.
authors.forename: Werner
authors.initials: W
authors.lastname: Ulrich
authors.affiliation: Hominid Paleobiology Doctoral Program, Center for the Advanced Study of Hominid Paleobiology, Department of Anthropology, George Washington University, Washington DC 20052, USA.
authors.forename: Amelia
authors.initials: A
authors.lastname: Villaseñor
authors.affiliation: Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington DC 20013, USA.
authors.forename: Scott
authors.initials: S
authors.lastname: Wing
authors.affiliation: Evolutionary Studies Institute, University of the Witwatersrand, Jorissen Street, Braamfontein, Johannesburg 2001, South Africa.
authors.forename: Heidi
authors.initials: H
authors.lastname: Anderson
authors.affiliation: Evolutionary Studies Institute, University of the Witwatersrand, Jorissen Street, Braamfontein, Johannesburg 2001, South Africa.
authors.forename: John
authors.initials: J
authors.lastname: Anderson
authors.affiliation: Department of Botany, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
authors.forename: Donald
authors.initials: D
authors.lastname: Waller
authors.affiliation: Department of Biology, University of Vermont, Burlington, Vermont 05405, USA.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Gotelli
mesh_terms: D000383:Agriculture / Q000266:history*; D000818:Animals; D017753:Ecosystem; D049690:History, Ancient; D006802:Human Activities / Q000266:history*; D006801:Humans; D009656:North America; D018521:Plant Physiological Phenomena; D011157:Population Dynamics; D013997:Time Factors