Germinación y establecimiento de plántulas de Pterocereus gaumeri, una cactácea columnar, rara y endémica de Yucatán, México

We examined the facilitative effect of nurse plants and the negative effect of predation on the germination and establishment of new individuals of Pterocereus gaumeri. The field experiment followed a factorial design, with five levels of association (four nurse plants and open space), four levels of orientation (North, South, East, and West) and two levels of predation (exclusion and non-exclusion of predators). There were no statistical differences between germination rates in open sites and under nurse plants, neither between nurse plants; however, seed germination was higher in the protected treatments. There were no statistical differences in the orientation factor for germination and survival. Seedling survival was higher under nurse plants than in open sites and seedling predation was very high. Our results showed that the recruitment of new individuals of P. gaumeri is a critical stage of the life cycle of the species and help explain the degree of rarity of this threatened cactus species.

Floral herbivory of an invasive slug on a native weed

Effects of floral herbivory (grazing flowers) by slugs on production and quality of seeds of herbaceous plants have been rarely quantified. We studied consequences of grazing by an invasive slug Arion lusitanicus (Mabille) for inflorescences of dandelion (Taraxacum officinale Weber ex Wiggers). In May 2008, a grassy site in Prague-Ruzyně (Czech Republic) was densely populated by dandelion inflorescences. Of the 40% of the flowers grazed by the slug, 70% died before seed dispersal and seed was eaten from 10% of the closed mature inflorescences. Viability of seeds from inflorescences that survived slug grazing was not affected. In addition to seedling predation, grazing of flowers may be an important source of dandelion mortality at sites where this slug is abundant.

Invertebrate predation of postdispersal seeds and juvenile seedlings of black spruce (Picea mariana) in the boreal forest of eastern Canada

We used an extensive vertebrate exclosure experiment to evaluate black spruce (Picea mariana (Mill.) B.S.P.) postdispersal seed and seedling predation by invertebrates in three boreal habitats of Eastern Canada: recent burn, spruce–moss, and lichen woodland. Between 9% and 19% of seeds were eaten by invertebrates. Seed predation was higher in recent burns than in spruce–moss and lichen woodlands. Abundance and diversity of potential invertebrate seed consumers sampled in pitfall traps also varied among habitat types. Among the invertebrate seed consumers sampled, Myrmica spp. (Hymenoptera: Formicidae) and Pterostichus adstrictus (Eschscholtz, 1823) (Coleoptera: Carabidae) were the most numerous; Formica spp. (Hymenoptera: Formicidae) and Pterostichus punctatissimus (Randall, 1838) (Coleoptera: Carabidae) were also present. Between 2% and 12% of juvenile black spruce seedlings were eaten by invertebrates. The most important seedling consumers were slugs (molluscs). Invertebrate predation of seeds and seedlings was highest (19% and 12%) in recent burns, indicating that invertebrate predation may significantly influence black spruce regeneration in these sites.

Impact of seed and seedling predation by small rodents on early regeneration establishment of black spruce

Black spruce (Picea mariana (Mill.) BSP) postdispersal seed and juvenile seedling predation by small rodents (Peromyscus maniculatus (Wagner), Clethrionomys gapperi (Vigor), and Phenacomys intermedius (Merriam)) was assessed in three boreal habitats over a 2-year period using an extensive exclosure–control experiment. Small rodent relative abundance was measured during six periods using snap trapping. We found that seed and juvenile seedling predation by small rodents varied according to habitat type and over time. Indeed, seed predation was higher in spruce–moss forests than in other habitats, notably during the winter of 2002. During this period, seedling predation was higher in recent burns. This period of higher seed and juvenile seedling predation corresponded to an increase in small rodent abundance in our study area. We suggest that seeds and juvenile seedlings can become important food sources for small rodents during winter when fresh and succulent vegetation is rare, as shown by results of seed predation. The impact of small rodents on the early regeneration of black spruce in the eastern Canadian boreal forest is thus an important factor to consider to better understand the forest regeneration process in this particular biome. Rodents can have a major effect on regeneration following a burn and can also contribute to poor seedling establishment from natural seed rain under mature cover.