Competition. Peter B. McEvoy Insect Ecology Ent 420/520. Prevalence of current competition in natural communities as judged by recent reviews. Schoener (1983) Connell (1983) Strong, Lawton, Southwood (1984) Lawton and Hassell (1984) Denno, McClure, Ott (1995). Review by Denno et al. .
Peter B. McEvoy
D judged by recent reviewsenno, R. F., M. S. McClure, and J. R. Ott. 1995. Interspecific interactions in phytophagous insects: Competition reexamined and resurrected. Ann. Rev. Entomol. 40:297-331.
A meta-analysis of 246 experimental contrasts between plants protected from herbivores versus plants exposed to herbivores
Herbivores often impose important effects on plant biomass -- equal in magnitude to those imposed by plant competition.
Effects of invertebrate herbivores are significantly stronger than those of vertebrates, in contrast to widely held views.
Thus future studies should investigate how herbivory and plant competition interact to determine the distribution, abundance, and diversity of plants.
Narrow niches with little overlap (d > w)
Broad niches with greateroverlap (d < w)
Decreasing d/w (increasing overlap) reduces likelihood of stable coexistence except for competitors with similar carrying capacities
As species diversity of ants increases, the variability in mandible length for Veromessor pergandei decreases
Mandible sizes of this species vary from site to site such that they always differ from those of local competitors (shown by arrows)
Minimum host size required for female progeny is larger for inferior competitorA. lingnanesis (right arrow) than for superior competitor A. melinus (left arrow) for red scale distributions on wood, leaves, fruits
Note differences in wing area and ovipositor length
Variegated leaf hopper
Increase with VLH relative density
Because risk of parasitism is higher in GLH than VLH, VLH contributes a small fraction of parasitoids even when VLH is an intermediate fraction (i.e. up to 50%) of the total hopper population but contribution accelerates thereafter
Successfully developed gall of Pemphigus betae on leaves of Populus angustifolia
(A) Percent aborted declines…
(B) Aphids per gall increases…
(C ) Stem mother weight increases..
…with increasing leaf size
Percent individual colonizing motherStem mothers seek out and colonize large leaves
Distribution of Leaves Available on Tree
Distribution of Leaves used by stem mothers
Territorial Aphids individual colonizing motherTypical fighting posture of Pemphigus betae females. The larger female usually wins the better territory, which is about 3 mm long at the base of the leaf
Intraspecific competition in females of the aphid individual colonizing motherPemphigus betaeWhen dominant female removed, displaced female moved down to occupy the better position
Points made goes to the aphid lower on the leaf
Not all leaves on tree are available or suitable
When available resources accurately defined, found to be limiting at least within tree (we don’t yet know tree to tree picture)
Points requiring further study
Host variability as defense against herbivores
Intertwining of suitable factors: nutrition, density of conspecifics, leaf abscission, enemiesConclusions from Pemphigus study
Platyptilia emissalisPTEROPHORIDAE is a congener of species studied by Karban
Karban surveyed patterns of association among plume moths (PM), spittlebugs (S), and thrips (T) along the length of the CA coast
Percentage of rosettes with each insect