Appendix 1 Definition of the main Allee effect-related concepts. Adapted from Berec
et al. (2007). The reference was given as followed.
Allee effect: a positive causal relationship between any component of fitness and
population density or size.
Component Allee effect: positive relationship between any measurable component of
individual fitness, such as reproduction and survival, and population size or density. A
population may suffer one to more component Allee effects. However, a component
Allee effect in a population may not always generate a demographic Allee effect,
which depends on more complex factors, such as life-history traits, resource
availability, predation and disturbance.
Demographic Allee effect: positive relationship between total individual fitness,
usually quantified by the per capita population growth rate, and population size or
density. The demographic Allee effect is defined as a strong Allee effect, if there is an
Allee threshold (critical population size or density below which the per capita
population growth rate becomes negative). Otherwise, it is called a weak Allee effect.
Ecological Allee effect: ecological-level mechanism resulting in a positive
relationship between any measurable fitness component and population size or
density.
Genetic Allee effect: genetic-level mechanism (such as sampling effect, genetic drift,
inbreeding) resulting in a positive relationship between any measurable fitness
component and population size or density.
Pollination-driven Allee effect: decreased reproduction or reproductive failure at low
density or in small populations due to decreased pollination success or pollination
failure, which is the most common and well-documented mechanism resulting in an
Allee effect in a plant species.
Predation-driven Allee effect: a general term for any component Allee effect in
survival or reproduction due to increased predation rate at low density or small prey
populations.
Reference
Berec L., Angulo E., Courchamp F. 2007. Multiple Allee effects and population
management. Trends in Ecology & Evolution 22, 185-191.
Appendix 2 An individual of Bombus richardsi was visiting Pedicularis rex, which is
a large subalpine herbaceous perennial and endemic to the East Himalaya. P. rex is
self-compatible but absolutely depends on bumblebees for reproduction in natural
populations.
Appendix 3 location of the focal patches of Pedicularis rex in 2011, dp represents
dense patch and sp indicates sparse patch. Patch size (the number of flowering
individuals) was indicated as the number in the parentheses. Sp1patch included only
one individual on an open space. The other three sparse patches (sp4, sp5 and sp6)
were distributed dispersedly along a narrow path downhill from sp1. Sp2 and dp5
patches belonged to a large population having hundreds of flowering individuals.
Dense patches were distributed much more continuously along another road downhill
from sp1.