EFFECTS OF BROWSING PRESSURE ON THE TEXTURAL CHARACTERISTICS OF JUNIPERUS COMMUNIS L. BRANCHES

In the Montseny Natural Park junipers scattered in the grasslands can be found. In some of these areas of the park, the breeding of small ruminants is allowed, while in others only find wildlife exists. Junipers develop differently if browsed, adopting spherical or conical morphotypes. This paper studies the mechanical characteristics of the shoots according to the sex of the bush and the branching regime to which they are subjected. 729 individual shoots were taken from male and female junipers exposed to browsing from goats and ewes and those not grazed and sampled at a different position from each bush. All the leaves were taken off the non-lignified end of the shot to be studied by a simulated bite. The strength needed to cut the apical twigs of junipers was measured using a Volodkevich jaw, which mimics the way incisors act, using a texturometer. The diameter of the branches differs according to bushes’ sex being larger for females and the individuals not exposed to predation pressure. Although the differences induced by sex were significant, differences due to grazing pressure were larger. The annual branches were thicker and longer in non-grazed junipers. This difference was not due to the partial consumption of the studied branches, as all the samples were collected in full. The continued browsing pressure leads to a survival strategy of growing, with branches tighter packaged as was evident in the analysis of the branching structure. The longer annual branches in non-grazed bushes allow for a more open structure. The force necessary to break the branch was significantly higher on females. This could be related to the fact that the females must bear the weight of the fruits. The elasticity of the annual shots was significantly higher on non-grazed junipers, a fact that could be considered as a way to tolerate herbivory.

Kleptopredation: a mechanism to facilitate planktivory in a benthic mollusc

Predation occurs when an organism completely or partially consumes its prey. Partial consumption is typical of herbivores but is also common in some marine microbenthic carnivores that feed on colonial organisms. Associations between nudibranch molluscs and colonial hydroids have long been assumed to be simple predator–prey relationships. Here we show that while the aeolid nudibranch Cratena peregrina does prey directly on the hydranths of Eudendrium racemosum , it is stimulated to feed when hydranths have captured and are handling prey, thus ingesting recently captured plankton along with the hydroid polyp such that plankton form at least half of the nudibranch diet. The nudibranch is thus largely planktivorous, facilitated by use of the hydroid for prey capture. At the scale of the colony this combines predation with kleptoparasitism, a type of competition that involves the theft of already-procured items to form a feeding mode that does not fit into existing classifications, which we term kleptopredation. This strategy of subsidized predation helps explain how obligate-feeding nudibranchs obtain sufficient energy for reproduction from an ephemeral food source.

Germination after simulated rat damage in seeds of two endemic Hawaiian palm species

Seed predation by native and alien rodents can limit plant recruitment and ultimately affect forest dynamics and composition (Campbell & Atkinson 2002, Côtéet al. 2003, Hulme 1998, Sánchez-Cordero & Martínez-Gallardo 1998). Even partial consumption of seeds by predators may affect plant community structure, though its importance is poorly understood (Steeleet al. 1993, Vallejo-Marínet al. 2006). Despite consumption of relatively large portions of seeds by herbivores, seeds can retain their ability to germinate if the embryo remains intact (Dalling & Harms 1999, Janzen 1972, Mack 1998). Germination of damaged seeds may be accelerated or prolonged (Karban & Lowenberg 1992, Koptur 1998, Vallejo-Marínet al. 2006). Damage by seed pests also facilitates ageing stress; which manifests as decreased seedling vigour, decreased seed viability, lower germination percentages and slower germination rates (Priestley 1986).