Results
Short-term effects of ant occupants and herbivores on A.
drepanolobium physiology- In wet seasons, Control trees had lowerAmax-leaf , lowerEleaf , and higher∆ψleaf in 2018 than in 2017, but
Transition trees exhibited no significant differences in any of those
traits (Amax-leaf :
F1,131 = 5.16, P = 0.0231, Fig. 1A;Eleaf : F1,131 = 8.99, P
= 0.0027, Fig. 1C; ∆ψleaf :
F1,122 = 3.88, P = 0.0488; Fig. 1E). During dry seasons,Amax-leaf was substantially lower in
2018 than in 2017 for newly-invaded trees, while Control trees exhibited
a significantly smaller interannual decline (F1,127 =
17.78, P < 0.01; Fig. 1B).Eleaf was significantly higher for
Control trees in 2018 than in 2017, while Transition trees remained
consistent across years(F1,127 = 4.53, P = 0.0332; Fig.
1D), trees at both sites exhibited consistent∆ψleaf in both years
(F1,127 = 0.00, P = 0.99; Fig. 1F).
Long-term effects of ant occupants and herbivores on Acacia
drepanolobium physiology - Trees occupied by C. mimosae vs.P. megacephala in long-term Uninvaded and Invaded sites differed
substantially in leaf water potential ranges, leaf gas exchange rates,
and canopy gas exchange capacities. During wet seasons, trees in Invaded
areas had reduced Amax-leaf(F1,205 = 11.55, P < 0.001; Fig. 2A),Eleaf (F1,205 = 15.68, P
<0.0001; Fig. S1A), Amax-canopy (F1,94 = 42.33, P < 0.0001; Fig. 2A), andEcanopy (F1,94 = 42.70,
P < 0.0001; Fig. S1A); however,∆ψleaf did not significantly vary
(F1,193 =1.39, P = 0.24; Fig. S1C). During dry seasons,
trees in Invaded areas had higherAmax-leaf (F1,212 =
4.55, P = 0.0329; Fig. 2B) andEleaf (F1,212 = 5.96, P
< 0.0001; Fig. S1B), but also slightly decreased∆ψleaf (F1,208 = 4.52, P
= 0.0334; Fig. S1D) by ca . 0.1 MPa; we did not find differences
in Amax-canopy (F1,53 =
0.06, P = 0.80; Fig. 2B) or Ecanopy(F1,53 = 0.49, P = 0.87; Fig. S1B) for long-term
sites.
During the rainy season, trees in Invaded areas that were exposed to
vertebrate herbivores had lower Amax-leaf (F2,205 = 5.03, P = 0.025; Fig. 3A),Amax-canopy (F2,94 =
53.07, P < 0.0001; Fig. 3C), andEcanopy (F2,94 = 50.30,
P < 0.0001; Fig. 4A), and non-significantly lowerEleaf (F2,205 = 2.99, P= 0.084; Fig. S2A); ∆ψleaf did
not differ (F2,193 = 0.20, P = 0.66). During the dry
season, invaded trees in each herbivory treatment did not differ inAmax-leaf (F2,212 =
1.94, P = 0.16; Fig. 3B), Amax-canopy(F2,53 = 1.71, P = 0.19; Fig. 3D), or∆ψleaf (P = 0.93; Fig. 4D), but tree in
Invaded areas that were exposed to vertebrates had slightly higherEleaf (F2,212 = 3.99, P= 0.0459; Fig S2B) and Ecanopy(F2,53 = 5.70, P = 0.0189; Fig. 4B).
Through ant removal in our factorial experiment, we linked occurrence ofP. megacephala ants with differences in water potential range and
gas exchange in both wet and dry seasons. During wet seasons, Invaded
trees that were experimentally cleared of P. megacephala had
higher Amax-canopy(F2,94 = 10.57, P < 0.001; Fig. 3C) andEcanopy (F2,94 = 10.77,
P < 0.001; Fig 3A), and slightly smaller∆ψleaf (F2,193 = 4.32, P
= 0.0378; Fig. 4C) by ca . 0.15 MPa; we did not find significant
differences in Amax-leaf(F2,205 = 0.19, P = 0.67; Fig. 3A) orEleaf (F2,205 = 0.07, P
= 0.79; Fig. S2A) on trees cleared of P. megacephala . In dry
seasons, trees occupied by P. megacephala had slightly higherEleaf (F2,212 = 6.36, P
= 0.0117; Fig S2B) and Ecanopy (F2,53 = 8.38, P = 0.0038; Fig. 4B) than P.
megacephala removal trees, but we found no differences between these
treatments in Amax-leaf(F2,212 = 0.01, P = 0.92; Fig. 3B),Amax-canopy (F2,53 =
3.11, P = 0.08; Fig. 3D), or ∆ψleaf (F2,208 = 2.57, P = 0.11; Fig. 4D). In contrast to
trees from long-term Invaded sites, trees occupied by C. mimosaeat Uninvaded sites did not exhibit different gas exchange or leaf water
potential traits due to ant removal, herbivore exclusion or their
interaction (Note S3).