Diversifying crop rotations with temporary grasslands - Université de ...
Diversifying crop rotations with temporary grasslands - Université de ...
Diversifying crop rotations with temporary grasslands - Université de ...
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Table 2<br />
Overview showing (i) mean seed predation rates for three weed species; (ii) coefficients of <strong>de</strong>termination of ANOVA mo<strong>de</strong>ls explaining ‘seed predation rates’ by ‘treatment’(R2 ); and (iii) coefficients of correlations between seed<br />
predation rates and canopy light interception (r). N = 20 for each weed species at each trial.<br />
Predator guild Trial 1 (April) Trial 2 (May) Trial 3 (July)<br />
Weed species Mean predation (%) ANOVA treatment (R 2 ) Correlation light (r) Mean predation (%) ANOVA treatment (R 2 ) Correlation light (r) Mean predation (%) ANOVA treatment (R 2 ) Correlation light (r)<br />
(A) Total<br />
A. myosuroi<strong>de</strong>s 21 ns ns 15 ns ns 51 0.42 † +0.46 *<br />
S. arvensis 12 0.49 * +0.47 * 2 ns +0.56 ** 47 0.48 * +0.59 **<br />
V. arvensis 58 0.85 *** +0.46 * 10 ns +0.44 † 58 0.46 * +0.52 *<br />
All species 30 0.21 * ns 9 ns +0.31 * 52 0.41 *** +0.52 ***<br />
(B) Vertebrates<br />
A. myosuroi<strong>de</strong>s 18 ns ns 13 ns ns 49 0.46 * +0.52 *<br />
S. arvensis 12 0.48 * +0.47 * 2 0.41 † +0.53 * 42 0.39 * +0.48 *<br />
V. arvensis 50 0.78 *** +0.52 * 8 ns +0.51 * 39 ns ns<br />
All species 27 0.25 ** +0.24 8 ns +0.34 ** 44 0.26 ** +0.32 *<br />
H. Meiss et al. / Agriculture, Ecosystems and Environment 138 (2010) 10–16 13<br />
(C) Invertebrates<br />
A. myosuroi<strong>de</strong>s 4 ns ns 4 ns ns 2 ns ns<br />
S. arvensis 1 ns ns 1 ns ns 4 0.54 * +0.37 †<br />
V. arvensis 9 ns −0.50 * 3 ns ns 24 ns +0.51 *<br />
All species 5 ns −0.23 † 3 ns ns 10 0.18 * +0.32 *<br />
ns, not significant.<br />
† p < 0.1.<br />
* p < 0.05.<br />
** p < 0.01.<br />
*** p < 0.001.<br />
was obtained by dividing the total amount of additive variance<br />
explained by ‘light interception’ by the total amount of additive<br />
variance explained by ‘treatment’.<br />
3. Results<br />
Seed predation rates varied consi<strong>de</strong>rably between the three<br />
trials (F 2,338 = 34.5, p < 0.0001, see Table 2 for mean values).<br />
Exclusion treatments (12 mm cages) suggested that vertebrates<br />
contributed much more to total seed losses than invertebrates<br />
(F 1,338 = 74.2, p < 0.0001). Predation rates also differed between the<br />
three weed species (F 2,338 = 13.1, p < 0.0001). Losses of V. arvensis<br />
seeds were highest during all periods and exclusion treatments<br />
except in May, where they were similar to A. myosuroi<strong>de</strong>s. Losses<br />
of S. arvensis were mostly lower than the two other species<br />
(Table 2).<br />
3.1. Impact of vegetation cover<br />
Weed seed predation was positively related to vegetation cover<br />
in most of the cases. In ANCOVA mo<strong>de</strong>ls, the additive effect of<br />
‘light interception’ was highly significant for Total (p < 0.0001)<br />
and Vertebrate predation (p = 0.0004), but not for Invertebrates.<br />
Moreover, several two or three-fold interactions between light<br />
interception, weed species and trial period were significant but<br />
explained less variance than the main effects. When analyzing<br />
each trial separately, Total seed predation was always positively<br />
related to light interception (Table 2). Correlations were strongest<br />
in the July trial (r = 0.52, p < 0.0001), intermediate in May (r = 0.31,<br />
p < 0.0149), but not significant in April (r = 0.19, p = 0.1491). For<br />
Vertebrates, correlations were always positive but again weakest<br />
in April. For Invertebrates, correlations were only significant<br />
in July, probably because Invertebrate predation rates were very<br />
low in April and May (Table 2). When looking at each weed<br />
species-trial combination separately, predation rates increased<br />
<strong>with</strong> vegetation cover in 15 out of 27 individual cases, correlations<br />
were not significant in 11 cases, mainly for treatments<br />
<strong>with</strong> low overall predation levels, and only one negative correlation<br />
was <strong>de</strong>tected for Invertebrates feeding on V. arvensis in April<br />
(Table 2).<br />
In three-way ANOVAs, the additive effect of ‘treatment’ was<br />
significant for Total (p < 0.0001), Vertebrate (p < 0.0001), and Invertebrate<br />
predation (p = 0.0175). Significant interactions <strong>with</strong> ‘trial<br />
period’ showed that the differences between the treatments differed<br />
<strong>with</strong> time. When calculating separate one-way mo<strong>de</strong>ls for<br />
each trial (but pooling all weed species), the differences between<br />
the treatments were significant for Total and Vertebrate predation<br />
but not for Invertebrates in April; differences were always<br />
significant in July but never in May, where predation rates were<br />
low in every <strong>crop</strong> (Table 2). A similar pattern appeared when<br />
analyzing each weed species-trial combination separately, but differences<br />
were more often significant for S. arvensis and V. arvensis<br />
than for A. myosuroi<strong>de</strong>s. In summary, 9 out of 27 individual mo<strong>de</strong>ls<br />
were significant at p < 0.05 and two at p < 0.1 (Table 2). In<br />
April, Total predation was high in all Medicago plots (averaging<br />
at 49%) and low in both Dactylis and bare soil plots (15–20%,<br />
Fig. 2). In May, predation was always low except in uncut Medicago,<br />
where it was significantly higher (20%). In July, the predation<br />
levels were highest in uncut Medicago and uncut Dactylis (both<br />
about 75%), lowest in bare soil plots (about 18%) and intermediate<br />
in cut Medicago (36%) and cut Dactylis (58%, see Fig. 2 for<br />
<strong>de</strong>tails). Cutting always had a negative impact, especially in Medicago,<br />
where it reduced the Total predation rates by about 53% in<br />
July and 77% in May, compared to 21% and 27% in Dactylis, respectively.