Data from: Interactions between fitness components across the life cycle constrain competitor coexistence

Numerous mechanisms can promote competitor coexistence. Yet, these
mechanisms are often considered in isolation of one another. Consequently,
whether multiple mechanisms shaping coexistence combine to promote or
constrain species coexistence remains an open
question.  Here, we aim to understand how multiple
mechanisms interact within and between life stages to determine
frequency-dependent population growth, which has a key role stabilizing
local competitor coexistence. We conducted field experiments in three
lakes manipulating relative frequencies of
two Enallagma damselfly species to evaluate demographic
contributions of three mechanisms affecting different fitness components
across the life cycle: the effect of resource competition on individual
growth rate, predation shaping mortality rates, and mating harassment
determining fecundity. We then used a demographic model that incorporates
carry-over effects between life stages to decompose the relative effect of
each fitness component generating frequency-dependent population
growth. This decomposition showed that fitness components
combined to increase population growth rates for one species when rare,
but they combined to decrease population growth rates for the
other species when rare, leading to predicted exclusion in most
lakes. Because interactions between fitness components within and
between life stages vary among populations, these results show that local
coexistence is population specific. Moreover, we show that multiple
mechanisms do not necessarily increase competitor coexistence, as they can
also combine to yield exclusion. Identifying coexistence mechanisms in
other systems will require greater focus on determining contributions of
different fitness components across the life cycle shaping competitor
coexistence in a way that captures the potential for population level
variation.