In the Pacific region,

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Planktivorous bluegill sunfish (Lepomis macrochirus) are known to consume large prey preferentially. Disagreement exists in the literature over whether this size—selectivity reflects optimal foraging behavior by the fish or relative prey encounter probability as predicted by a model in which apparent size of the prey determines foraging preferences. As bluegills grow larger, their visual resolution increases, and this should affect prey choice under the apparent size model. In laboratory experiments, three sizes or fish were fed identical diets made up of three sizes of Daphnia magna. Large and medium—size fish consumed relatively more large prey than predicted by the apparent size model, whereas the diet of small fish deviated only sightly from the apparent size model. For fish to be more selective than allowed by the apparent size model, they must be able to estimate absolute prey size. To do this requires good vision. Since diet selectivity was highly significantly correlated with the fishes' visual resolution in our experiments, we suggest that visual capability imposes a constraint on the ability of small bluegills to choose prey.

1. The earliest exotic records for two notorious invasive ants, the big-headed ant ( Pheidole megacephala ) and the Argentine ant ( Linepithema humile ), both come from the Atlantic islands of Madeira, where the two species underwent population explosions in the 1850s and 1890s respectively. Researchers have long assumed that these invaders spread across all of Madeira and exterminated most or all native ants, despite no research actually documenting such impact.2. Re-examination of first-hand nineteenth century accounts suggest that P. megacephala and L. humile may never have spread beyond coastal lowland areas, representing < 10% of Madeira's land area. In 2002, native ants dominated most of Madeira; P. megacephala and L. humile were restricted to ≈ 0.3% and ≈ 6% of Madeira's land area respectively.3. Of the 10 native ant species known from Madeira, only one ( Temnothorax wollastoni ) was not present in 1999 -2002 surveys. Although exotic ants may have exterminated T. wollastoni , it seems likely that this species still survives. 4. Thus, even after 150 or more years of residence, P. megacephala and L. humile have come to occupy only a small part of Madeira, and appear to have had little impact.5. Most of Madeira may be too cool for P. megacephala and perhaps too moist for L. humile to dominate. Also, Madeira's vast natural areas may generally lack weedy vegetation that can support high densities of plant-feeding Hemiptera critical for the ecological dominance of invasive ants. Finally, a dominant native ant, Lasius grandis , inhabiting ≈ 84% of Madeira, may actively exclude P. megacephala and L. humile .

In the leaf-cutting ant Atta cephalotes (L.) small colonies produce a relatively narrow size-range of small workers, whereas large colonies produce a much wider size-range of workers. In this study, I compared the foraging of four small A. cephalotes colonies (fewer than 5000 workers) with published data on foraging of large colonies to examine how colony size and worker size-range may be related to foraging ecology in leaf-cutting ants. I found that the foraging ecology of small A. cephalotes colonies is very different from that of large colonies. In small colonies, a relatively narrow size-range of foragers (1.4-6.7 mg, mean 3.3 mg) cut primarily "herbs" (ferns, grasses, and other small herbaceous plants) located within 7 m of the nest. In contrast, in large colonies, a broader size-range of workers (1.4-30 mg, mean 7.3 mg) participate in foraging, generally harvesting from trees 20-80 m from the nest, with larger workers cutting on trees with thicker and tougher leaves. Small colonies' dependence on small herbaceous plants near the nest may have a profound impact on distribution of A. cephalotes. A. cephalotes colonies are rarely found in primary forest, where the low occurrence of small herbaceous plants in the understory may preclude the establishment of young colonies.

Complete 16S-like ribosomal RNA coding regions were obtained from the fungal symbiont of five genera of attine (leaf-cutting) ants and two free-living fungi. Phylogenetic analyses with distance matrix, maximum likelihood, and parsimony methods revealed that the attine fungal symbionts are homobasidiomycetes in the order Agaricales. Comparison of the topology of the attine fungal symbiont phylogenetic tree with a tree based on attine ant morphology revealed a congruent branching pattern of the more derived attine ants and their fungal symbionts. The parallel branching pattern suggests a long-term coevolution of derived leaf-cutting attine ants and their fungal symbionts.

Two models proposed to explain prey selection by visually foraging planktivorous fish, the reactive field volume model (RFVM) and the apparent size model (ASM), have been found to yield similar dietary predictions in many situations. However, we found earlier formulations of the ASM to be incorrect. The correct predictions of these two models were compared. Published empirical data from an earlier fish foraging study were reanalyzed and found to fit both models quite well. Interpretation of data from an unpublished study, performed under conditions that should have allowed discrimination between the two models, was somewhat ambiguous. When we performed a similar study the results were consistent with the predictions of the ASM, but differed very significantly from those of the RFVM.