title: Evidence from individual inference for high-dimensional coexistence: long-term experiments on recruitment response.
abstract: BACKGROUND
  For competing species to coexist, individuals must compete more with others of the same species than with those of other species. Ecologists search for tradeoffs in how species might partition the environment. The negative correlations among competing species that would be indicative of tradeoffs are rarely observed. A recent analysis showed that evidence for partitioning the environment is available when responses are disaggregated to the individual scale, in terms of the covariance structure of responses to environmental variation. That study did not relate that variation to the variables to which individuals were responding. To understand how this pattern of variation is related to niche variables, we analyzed responses to canopy gaps, long viewed as a key variable responsible for species coexistence.
  
  
  RESULTS
  A longitudinal intervention analysis of individual responses to experimental canopy gaps with 12 yr of pre-treatment and 8 yr post-treatment responses showed that species-level responses are positively correlated--species that grow fast on average in the understory also grow fast on average in response to gap formation. In other words, there is no tradeoff. However, the joint distribution of individual responses to understory and gap showed a negative correlation--species having individuals that respond most to gaps when previously growing slowly also have individuals that respond least to gaps when previously growing rapidly (e.g., Morus rubra), and vice versa (e.g., Quercus prinus).
  
  
  CONCLUSIONS
  Because competition occurs at the individual scale, not the species scale, aggregated species-level parameters and correlations hide the species-level differences needed for coexistence. By disaggregating models to the scale at which the interaction occurs we show that individual variation provides insight for species differences.
authors.affiliation: Nicholas School of the Environment, Duke University, Durham, North Carolina, United States of America. jimclark@duke.edu
authors.forename: James S
authors.initials: JS
authors.lastname: Clark
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Soltoff
authors.forename: Amanda S
authors.initials: AS
authors.lastname: Powell
authors.forename: Quentin D
authors.initials: QD
authors.lastname: Read
mesh_terms: D000220:Adaptation, Biological; D000818:Animals; D044822:Biodiversity; D003247:Conservation of Natural Resources; D004463:Ecology / Q000379:methods*; D004777:Environment; D008137:Longitudinal Studies; D008954:Models, Biological; D008962:Models, Theoretical; D031625:Morus / Q000502:physiology; D018521:Plant Physiological Phenomena; D010944:Plants / Q000378:metabolism; D011157:Population Dynamics; D011237:Predictive Value of Tests; D029963:Quercus / Q000502:physiology; D013045:Species Specificity; D013997:Time Factors