Within-species responses to abiotic and biotic factors
Within species, vital and population growth rate responses to abiotic
heterogeneity in shade and soil separated into three distinct response
profiles. One species, P. airoides , exhibited clear evidence of
demographic compensation, whereby a convex emergence response to PC1
coupled with a negative seed production response resulted in a
non-significant population growth rate response (Fig. 2). For a further
five species (all but A. calendula and H. glutinosum ), we
found similar compensatory trends along PC1 between emergence and seed
production, but relationships were only significant for one of the vital
rates (mainly emergence). Hence, most of the species (6/8) had one
significant vital rate response (positive or convex) to PC1 yet a
non-significant population growth response (Fig. 2). Hyalosperma
glutinosum had a positive emergence response to PC1 but no other
significant vital or population growth responses (Fig. 2). The final
species, A. calendula , had no significant responses of any vital
rate or population growth rate to PC1 (Fig. 2).
There were three response profiles for the influence of neighbour
abundance (or presence for population growth) on vital and population
growth rates within species. Most of the species (6/8) had
non-significant vital and population growth rate responses (Fig. 3,
Table S2). One species, P. debilis , produced fewer seeds as
neighbour abundance increased and had lower population growth rates in
the presence of neighbours (Fig. 3). Arctotheca calendula did not
have significant survival or seed production responses to neighbour
abundance yet had lower growth rates in the presence of neighbours (Fig.
3). For most species, within-species population growth responses to
neighbours were in the same direction as seed production responses (for
6/8 species) and survival responses (for 5/8 species, Table S2). Two
species had significantly lower population growth rates in the presence
compared to absence of neighbours (Fig. 3, Table S2,p <0.05).
The LTRE analysis showed that the life stage transitions contributing
most to the difference in population growth rate in the absence versus
presence of neighbours differed for the two species assessed. Survival
probability and seed production were the only rates allowed to vary
between population growth rates as they were the only vital rates
measured in response to neighbour removal. For A. calendula , the
transition representing a dormant seed remaining viable, emerging, and
surviving to reproduction made the largest contribution (52%, Figure
S5). This contrasted to P. debilis , for which the transition
representing an adult plant producing seeds that stays dormant and
viable in the seed bank accounted for 73% of the difference in
population growth between neighbour treatments.