TY - JOUR
T1 - An empirical test of the mechanistic underpinnings of interference competition
AU - Beggs, Richard
AU - Pierson, Jennifer
AU - Tulloch, Ayesha I.T.
AU - Blanchard, Wade
AU - Westgate, Martin
AU - Lindenmayer, David
N1 - Funding Information:
a). In addition, we monitored changes in harassment rates to see if interference competition by the dominant aggressor, or other aggressive species associated with high Improvements in opportunities for foraging and reproduction are essential if vulnerable species are to recover in the longer term. Hence, for this experiment we monitored changes in foraging opportunities (reported here) and reproductive potential (Beggs et al. M. melanocephala densities, is the reason that small woodland birds are unable to access resources in sites colonised by M. melanocephala . We showed that even modest reductions in abundance of the dominant aggressor resulted in greater resource availability for some small woodland birds for up to six months. We were unable to show that this was due to less interference competition so our attempt to link the impact of interference competition to resource availability was not wholly successful. , Cunningham et al. 2014b, Ikin et al. 2014, Bennett et al. ), even if the threat from Manorina melanocephala has a preference for small, degraded woodland remnants in fragmented landscapes (Oldland et al. 2009, Maron et al. 2013). Such habitat may have a limited capacity to support recovery of target species (Ford M. melanocephala is mitigated. Well‐designed ecological restoration, particularly where a shrub layer is included, is believed to both deter , Clarke and Grey 2010, Tulloch et al. b, Lindenmayer et al. ). Managing resource supply through ecological restoration may therefore be a suitable complementary policy to managing resource demand through culling of interference competitors. M. melanocephala and support declining small woodland birds (Hastings and Beattie Acknowledgements – The authors are grateful to the landowners for granting access to their land for the study. Funding – The research was supported by Birdlife Australia, the Holsworth Wildlife Endowment and the Australian Government's National Environmental Science Program through the Threatened Species Recovery Hub. Permits – Approval for the cull was granted by the New South Wales Office of Environment and Heritage and ethics approval was given by the Australian National University's Animal Ethics and Experimentation Committee (protocol A2016/04). Supplementary material (available online as Appendix oik‐06583 at < www.oikosjournal.org/appendix/oik‐06583 >). Appendix 1.
Publisher Copyright:
© 2019 Nordic Society Oikos. Published by John Wiley & Sons Ltd.
PY - 2020/1/1
Y1 - 2020/1/1
N2 - 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 such aggression and wastes energy in evasive responses. Studying competition is notoriously difficult, however, empirical evidence of the resource availability theory is limited, and there are few published experimental studies showing such an effect at larger scales. We present the results of a controlled and replicated empirical study of interference competition at a landscape scale. We removed an aggressive, overabundant native bird, Manorina melanocephala (noisy miner), 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 M. 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, however, 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 abundance of M. melanocephala, make it difficult to draw firm conclusions about the relationship between rates of harassment and rates of foraging.
AB - 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 such aggression and wastes energy in evasive responses. Studying competition is notoriously difficult, however, empirical evidence of the resource availability theory is limited, and there are few published experimental studies showing such an effect at larger scales. We present the results of a controlled and replicated empirical study of interference competition at a landscape scale. We removed an aggressive, overabundant native bird, Manorina melanocephala (noisy miner), 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 M. 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, however, 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 abundance of M. melanocephala, make it difficult to draw firm conclusions about the relationship between rates of harassment and rates of foraging.
KW - cull
KW - foraging
KW - harassment
KW - interference competition
KW - Manorina melanocephala
KW - noisy miner
KW - overabundant native species
KW - population control
UR - http://www.scopus.com/inward/record.url?scp=85074560067&partnerID=8YFLogxK
U2 - 10.1111/oik.06583
DO - 10.1111/oik.06583
M3 - Article
AN - SCOPUS:85074560067
SN - 0030-1299
VL - 129
SP - 93
EP - 105
JO - OIKOS
JF - OIKOS
IS - 1
ER -