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Insect Seed Predators (insect + seed_predator)
Selected AbstractsSpatial Variation in the Strength of a Trophic Cascade Involving Ruellia nudiflora (Acanthaceae), an Insect Seed Predator and Associated Parasitoid Fauna in MexicoBIOTROPICA, Issue 2 2010Luis Abdala-Roberts ABSTRACT Spatial variation in the strength of herbivore top-down control represents an important source of variation in plant fitness measures and community structure and function. By measuring seed predator (larvae of a Noctuid moth) and parasitoid impacts on Ruellia nudiflora across a broad spatial scale in Yucatan (Mexico), this study addressed the following: (1) to what extent does seed predator and parasitoid attack intensity associated with R. nudiflora vary spatially? (2) Does parasitoid attack result in a positive indirect effect on the plant, and does the intensity of this effect vary spatially? During the peak of fruit production (late June,early July) of 2005, we collected fruits from 21 R. nudiflora populations and grouped them into four regions: center, east, north and south. For each fruit we recorded: observed seed number, number of seeds eaten, seed predator presence, parasitoid presence and number of seeds ,saved' by parasitoids. Seed predators attacked ca 30 percent of fruits/plant on average, while parasitoids were found in 24 percent of seed predator-attacked fruits. Results indicated spatial variation in seed predator and parasitoid attack levels; interestingly, a contrasting spatial gradient of attack intensity was observed: populations/regions with greatest parasitoid attack levels usually had the lowest seed predator attack levels and vice versa, suggesting top-down control of parasitoids on seed predators. We observed a weak overall indirect impact of parasitoids on R. nudiflora (4% seeds ,saved' on average), which nonetheless varied strongly across populations (e.g., close to 14% seeds saved at one population). Findings indicate a geographical structuring of interaction strengths across populations, as well as spatial variation in the strength of parasitoid cascading effects on plant reproduction. Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp [source] When do localized natural enemies increase species richness?ECOLOGY LETTERS, Issue 4 2005Frederick R. Adler Abstract The Janzen,Connell hypothesis states that local species-specific density dependence, mediated through specialist enemies of offspring such as fungal pathogens and insect seed predators, can facilitate coexistence of species by preventing recruitment near conspecific adults. We use spatially explicit simulation models and analytical approximations to evaluate how spatial scales of offspring and enemy dispersal affect species richness. In comparison with model communities in which both offspring and enemies disperse long distances, species richness is substantially decreased when offspring disperse long distances and enemies disperse short distances. In contrast, when both offspring and enemies disperse short distances species richness more than doubles and adults of each species are highly spatially clumped. For the range of conditions typical of tropical forests, locally dispersing specialist enemies may decrease species richness relative to enemies that disperse long distances. In communities where dispersal distances of both offspring and enemies are short, local effects may enhance species richness. [source] Seed predation during general flowering events of varying magnitude in a Malaysian rain forestJOURNAL OF ECOLOGY, Issue 4 2007I-FANG SUN Summary 1The lowland dipterocarp forests of Southeast Asia exhibit interspecifically synchronized general flowering (GF) and mast fruiting at irregular multi-year intervals of 1 to 11 years. The predator satiation hypothesis (PSH) posits that GF events enhance seed survival by reducing the survival, reproduction and population sizes of seed predators between GF events, and then satiating the reduced seed predator populations during GF events. 2Three GF events of different magnitudes occurred in Pasoh Forest Reserve, Peninsular Malaysia, during 2001, 2002 and 2005. We exploited this natural experiment to test two predictions of the PSH. The first prediction was that seed survival should increase with the magnitude of the GF event. The second prediction was that seed predation should decrease with time since the previous GF event. 3A reproductive survey of all (c. 900) dipterocarp trees 30 cm d.b.h. in a 50 ha plot showed that flowering pervasiveness (the proportion of dipterocarp species participating) was high and similar in all three GF events. However, relative flowering magnitudes (measured by an index of individual tree participation and flowering intensity in Shorea species) were 2, 5 and 8 for the 2001, 2002 and 2005 GF events, respectively. 4The percentage of Shorea seeds surviving pre- and post-dispersal predation increased with the magnitude of GF events, which is consistent with the first prediction. 5Pre-dispersal insect seed predators consumed 12.9%, 11.2% and 3.4% of Shorea seeds in the 2001, 2002 and 2005 GF events, respectively, which is consistent with both predictions. 6Pre-dispersal seed predation by primates (mainly leaf monkeys) increased from 11.9% to 38.6% then fell to 9.3% in the 2001, 2002 and 2005 GF events, respectively. 7Predator satiation occurred only at population and community levels. At the individual tree level there was no relationship between the percentage of seeds surviving pre- and post-dispersal seed predation and variation in seed crop size or seed density beneath the tree. This suggests that attempts to test the PSH on the scale of individual trees may miss key community level effects. 8Our results suggest a more significant role of pre-dispersal seed predation in the evolution of reproductive synchrony than was recognized in the original statement of the PSH. [source] The role of rainfall and predators in determining synchrony in reproduction of savanna trees in Serengeti National Park, TanzaniaJOURNAL OF ECOLOGY, Issue 1 2007SIMON A. R. MDUMA Summary 1We examined the factors determining synchrony in reproduction in nine Acacia and six other tree species in the Serengeti ecosystem. 2We test two hypotheses: (i) an abiotic hypothesis where the primary determinant of synchrony is an adaptation to water availability; and (ii) biotic hypotheses where these adaptations to water can be further refined by additional adaptations to avoid predators, or attract seed and fruit dispersers. 3Flowering and fruiting were recorded monthly for individually marked trees during 1997,2004. Flowering in different species occurs semi-annually, annually or, in the case of one species, once every 2 years. For most species synchrony of flowering was correlated with seasonal rainfall, with lags related to the mean height of the species; small species flowered during the rains while larger species flowered in the dry season. Fruiting seasons occurred at the end of the rains irrespective of the flowering season. 4Most species showed flowering synchrony greater than expected from the distribution of rainfall. This may be related to avoidance of insect seed predators through predator satiation. Two Acacias showed multi-annual fruiting (masting), possibly as a predator avoidance mechanism. Acacia tortilis has two flowering seasons: a dry season flowering with early abortion of pods and a wet season flowering producing successful fruits. 5Two species of Commiphora appeared to be synchronized so as to attract birds that disperse seeds. Acacia tortilis produced indehiscent pods attractive to ungulates, possibly to kill bruchid beetles during digestion and so increase seed viability. 6Our results suggest that synchrony in these trees is caused by a strong interaction between abiotic and biotic factors. Closely related species have different reproductive patterns of synchrony that seem to be adapted to different combinations of rainfall, predators and dispersers. Rainfall is the primary determinant but the activities of predators and dispersers increase the degree of synchrony. [source] | ||||||||||