DOI: 10.5061/dryad.n8d6g1s
title: Data from: An empirical test of the mechanistic underpinnings of interference competition

description: Interspecific competition is an essential element of the evolution of
 species and can strongly influence the abundance and distribution of
 species. Where competition interacts with anthropogenic habitat
 modification, this natural ecosystem process can become a threatening
 process. Understanding the mechanisms behind competition in such cases is
 essential for the formulation of cost-effective management responses for
 biodiversity conservation. According to the resource availability
 hypothesis of competition, interference competition limits access to
 resources by species vulnerable to aggression and wastes energy in evasive
 responses. Studying competition is notoriously difficult, however,
 empirical evidence of the resource availability hypothesis is limited, and
 there are few published experimental studies showing the effect at larger
 scales. We present the results of a controlled, replicated empirical study
 of interference competition at a landscape scale. We removed an
 aggressive, overabundant bird, Manorina melanocephala, whose interference
 competition is a threatening process for small woodland birds in the
 highly modified agricultural landscapes of eastern Australia. We monitored
 foraging and harassment rates of small woodland birds before and after
 removal to indicate if levels of interference competition changed. Due to
 unexpected immediate recolonisation, abundance of Manorina melanocephala
 in treatment sites declined by only 34% relative to control sites.
 Twenty-four bird species displayed aggressive behaviour towards other
 birds and 41 bird species were victims of aggression. Manorina
 melanocephala was responsible for 66% of all aggressive interactions.
 After removal, we recorded a doubling in foraging rate of small woodland
 birds in treatment compared to control sites. This appears to confirm the
 resource availability hypothesis of competition. Paradoxically, increased
 foraging was not accompanied by a decline in harassment. Low detection
 rates of harassment of small woodland birds, combined with the modest
 reduction in Manorina melanocephala abundance, make it difficult to draw
 firm conclusions about the relationship between rates of harassment and
 rates of foraging.
description: Oikos Harassment
 DataColumn letter Column
 name Meaning E Repeat Number of survey that year (out of 8) G Temp
 Estimate of ambient temperature (scale 1-4) H Wind Estimate of windspeed
 (Scale 1-4) I Cloud cover Estimate of cloud cover (Scale 1-4) J Cloud%
 Estimate of cloud cover (%) K Harassment_id Chronological number of
 harassment event in that survey O-Q Canopy, aerial, ground Location of
 harassment event R-U Chase, supplant, harass, Posturing Type of harassment
 event W-Y Retreat, leave patch, fight back Response of victim Z Witnessed
 duration Duration of harassment event AA SWB Was the victim a small
 woodland bird? (1=yes, 0=no) AB Site Made up of Farm + Treatment AC-AO
 Site characteristics AP NM_aggression Was the aggressor species noisy
 miner? (1=yes, 0=no)Oikos Foraging
 DataColumn letter Column
 name Meaning E Repeat within year Number of survey that year (out of 8) F
 Time Time of day G Temp Estimate of ambient temperature (scale 1-4) H Wind
 Estimate of windspeed (Scale 1-4) I Cloud% Estimate of cloud cover (%)
 J-AR Small woodland bird species observed foraging (_forag) and not
 foraging (see Appendix in manuscript for meaning of species abbreviations)
 AR Sum Sum of foraging events for that survey AS Site Made up of Farm +
 Treatment AT-BD Site characteristics