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Our results showed that trapped seeds have the same ability to germinate as normally released seeds, but that they differ from normal seeds in weight and shape. After performing three different studies to examine this phenomenon, we found that, on average, 34% of individual wild cucumber fruits contained additional trapped seeds which could not be released. Research was conducted in riparian habitats in the central part of Poland. Here, we describe a new kind of physical protection in the wild cucumber (Echinocystis lobata) in its invasive range: the production, in the central part of the fruit’s fibre frame, of 1 or 2 additional seeds which cannot be released. A given plant’s effective defence of its seeds from seed predators ensures its survival. Seed predators have a strong effect on the seed banks, seedling recruitment, and establishment of a plant population. Invasive alien plant species in a new location usually lose their native enemies, but new interactions with local herbivores can also significantly influence their population dynamics. Different foraging behaviors influence the form of selection exerted by these two seed-eating species. However, red squirrels preferred feeding on small and medium larch cones, favoring trees producing large cones. The great spotted woodpecker preferred foraging on cones with thinner peduncles resulting in selection for thicker peduncles. In this study, we documented different selection pressures on European larch (Larix decidua) cones exerted by great spotted woodpecker (Dendrocopos major) and red squirrels (Sciurus vulgaris). We collected 350 foraged larch cones from each anvil and feeding place for both species and also 50–100 unforaged larch cones within a 15 m radius at each site. We selected 10 anvils for great spotted woodpecker and 12 foraging places for the red squirrel. The study was conducted in mixed mountain forests in West Sudetes (50★5’N 15☄6′E), southwest Poland. In response to such selection, many conifers invest resources in various physical and chemical seed defenses.
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Specialized conifers-seed-eating animals, such as crossbills (Loxia spp.), woodpeckers (Picidae), squirrels (Sciuridae), nutcrackers (Nucifraga spp.) and many of insects (e.g., Pyralidae and Tortricidae) exert phenotypic selection on different features of the coniferous cones.
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