Invasion outcomes and the diversity-stability
relationship
The effects of invasion on community stability and diversity observed in
our simulations depend on the outcome of the invasion. Invasion-induced
destabilisation occurs primarily under vulnerability, where it almost
always leads to community collapse (regime states E→N andO→N ; Figs. 4 and S8, Tables S9–S11). More than half of the
invasions leading to integration and some leading to substitutions also
trigger a loss of stability, with invasion-induced cycles replacing
equilibrium (E→O ). We do not observe invasion-induced
destabilisation under resistance, occupancy and rescue mechanisms. An
invasion-triggered increase in stability, which would prevent a complete
collapse of the resident community and is characteristic of the rescue
(N→E ), occurs less frequently under occupancy (N→E andN→O ) and integration (N→O ). An invasion-triggered increase
in stability associated with a shift from oscillations to stable
equilibria (O→E ) is rare and occurs only under substitution and
vulnerability (Fig. S1a).
As a result, we find that invasion-induced changes in diversity and
stability are interrelated, but one cannot be predicted from the other
alone (Fig. 4b). Diversity loss (ΔD < 0) is almost
always associated with invasion-induced loss of stability (ΔS
< 0). No net change in diversity (ΔD = 0) is mostly
associated with no change in stability as expected, but loss of
stability (invasion-induced cycles in EC) or increased stability (dampen
cycles induced by invasion through species substitution in
IGPP) also occur as a result of invasion. Interestingly,
invasions leading to increased diversity (ΔD > 0)
have the most evenly distributed effects on stability. About one third
of the simulations each lead to reduced, increased or unchanged
stability across species mass ratios, food web topologies and
environmental conditions (Fig. 4b).