Species-specific disturbance tolerance, competition and positive interactions along an anthropogenic disturbance gradient

Authors

  • Tania Villarreal-Barajas,

    1. Departamento de Ecología y Recursos Naturales, Facultad de Ciencias, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510 México D.F., Mexico
    2. E-mail trisomia22@hotmail.com
    Search for more papers by this author
  • Carlos Martorell

    Corresponding author
    1. Departamento de Ecología y Recursos Naturales, Facultad de Ciencias, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510 México D.F., Mexico
      *Corresponding author; E-mail martorel@ecologia.unam.mx
    Search for more papers by this author

  • Coordinating Editor: H. Henrik Bruun.

*Corresponding author; E-mail martorel@ecologia.unam.mx

Abstract

Question: As it has been found that stress promotes positive interactions mediated by physical amelioration of the environment, is it possible that interactions may turn positive with increasing chronic anthropogenic disturbance (CAD) intensity? Also, is it possible that species that do not tolerate disturbance may require environmental amelioration by their neighbours in disturbed areas, whereas tolerant species may not?

Location: The semi-arid grassland in Concepción Buenavista, Oaxaca, southern Mexico.

Methods: We assessed interaction intensity and importance through a neighbour removal experiment along a CAD gradient for three species differing in disturbance tolerance. Water potential was monitored on vegetated and bare soil.

Results: A shift from competitive effects in low CAD sites to positive interactions in degraded sites was found. The disturbance-tolerant species did not respond to CAD, whereas the less tolerant species changed its interactions drastically in terms of growth and reproduction. The species with medium tolerance had an intermediate response. Neighbours promoted germination in all species. Vegetation removal reduced soil humidity.

Conclusions: Positive interactions seemingly resulted from the amelioration of the abiotic stresses induced by vegetation removal. The dependence on neighbours to germinate, grow, or reproduce suggests that if CAD eliminates the plant cover, vegetation will hardly recover. Irreversible changes are known to occur in communities where positive interactions predominate, but CAD may set the conditions for irreversible shifts even in communities where interactions are normally competitive.

Ancillary