Diversifying crop rotations with temporary grasslands - Université de ...

D.III.3 Factors determining weed seed predation
Two factors were studied in detail that may affect the weed seed predation rate (differences
between weed species and the impact of vegetation cover). Obviously, there may be numerous
other factors that should be taken into account in a predictive model. To facilitate the
development of future models, the large variety of factors might be organized according to a
rather simple scheme based on 4 groups (illustrated in Fig. 25):
(i) factors determining weed seed presence and abundance, such as weed population
densities, plant phenology determining the target period between seed shed and seed
germination, spatial seed distribution and seed burial (Marino et al., 2005; Heggenstaller
et al., 2006; Westerman et al., 2008);
(ii) species-specific seed traits such as mass, size, seat coat and other physical and chemical
characteristics determining seed attractiveness, palatability and nutritional value (White
et al., 2007) that would be at the origin of the consistent weed species preference order
observed in the 2007 and 2008 seed predation experiments (cf. chapter C.IV and general
discussion ;
(iii) factors determining seed predator presence, abundance and activity such as the regional
predator species pool, predator dispersal abilities (Macdonald et al., 2000b) and the local
presence of favourable habitats for foraging and reproduction, as well as antagonists of
the predators such as carnivores or parasitoids (Hulme, 1997; Van Klinken, 2005) (one
of the most important factors determining habitat quality might be vegetation cover
studied in Article 8);
(iv) the species-specific diet, preferences and behaviour of the seed predators which may
vary according to the presence of alternative food items and the current energy need
(hunger) of the predators.
‘Seed availability’ and ‘seed demand’ (Westerman et al., 2003c) will thus be determined by (i)
and by (iii)+(iv), respectively.
176