Keystone Fruit Resources and Australia’s Tropical Rain Forests

Most host-specificity studies of tropical rainforest insects have focused on those species feeding on leaves. Apart from the fruit flies, the level of specialisation among fruit-associated insects is poorly known. The relative contribution to local species richness made by insects feeding or associated with fallen fruits is also unknown. Beetles from fruit falls over a 5-year period in lowland tropical rainforest at Cape Tribulation, Australia were sampled. A total of 5157 individual beetles of 73 species were sampled from the fruits of 18 different plant species. Only a few species were of frugivorous families, and most species are likely utilising resources associated with the breakdown of the fruits. The size of the fruit fall-associated beetle assemblage (73 spp) was small compared with the number of species collected during a 4-year sampling program conducted at the same site prior to the current study using 10 combined Malaise-Flight Interception Traps (1473 spp, 77 families). The number of beetles and species collected from fruit that were very strongly correlated with the number of times fruit falls from a particular species of plant were sampled. The locally common palm, Normanbya normanbyi, produced fruit throughout the year and supported the largest number of fruit-associated species. It is suggested that this might be a keystone resource for local fruit fall-associated insect species. Although most beetle species showed a preference for the fruits of a particular plant species, overall host specificity for beetles was low. This is probably because fruit resources at this site are spatially and temporally patchy. Our results challenge the notion that most insects associated with fruit falls in tropical rainforests are highly host-specific.

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“…; Westcott et al . ; Inkrot et al . ), and this is also likely to limit the number of beetle species using such a resource.…”

Section: Discussionmentioning

confidence: 99%

“…Westcott et al . () suggest that there is no such thing as keystone fruit resources for frugivorous vertebrates, although individual species contributions can be very large on a local scale.…”

Section: Discussionmentioning

confidence: 99%

Low host specificity of beetles associated with fruit falls in lowland tropical rainforest of north‐east Australia

et al. 2013

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“…(2005b), (>20 ml) and 27 (48%) were large seeded as defined by Stocker and Irvine (1983), (> 8 ml). Using Westcott et al 's (2005b) conservative definition, a significantly greater proportion of large‐seeded species occurred in the diet than occurs at the study area generally, (χ 2 = 7.41, df = 1, P < 0.01).…”

mentioning

confidence: 94%

“…The 250 species from the study site for which we collected fruit characteristic data were grouped into phenological classes based upon annual, biennial, or continuous (both synchronous and asynchronous) fruiting. Species were assigned to these classes on the basis of phenological data collected during the 68 mo of this study, Westcott et al (2005b), and M. Bradford, unpublished data). Species classified as ‘annual’ are those which fruit for a short period (1–8 mo) every year at a similar time of year; ‘biennial’ species fruit for a short period at intervals greater than one year but at a similar time of the year; and ‘continuous’ species fruit constantly throughout the year (≥ 9 mo of the year).…”

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confidence: 99%

“…Both mean fruit width and mean seed width of species in cassowary diets were significantly higher than those of species recorded at the study area and not in the diet ( t =−4.13, df = 239, P < 0.001; t =−3.80, df = 220, P < 0.001, respectively). Of the 56 fruit species we recorded from cassowary droppings, 15 (26.8%) were large seeded as defined by Westcott et al . (2005b), (>20 ml) and 27 (48%) were large seeded as defined by Stocker and Irvine (1983), (> 8 ml).…”

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confidence: 99%

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Diet and Dietary Preferences of the Southern Cassowary (Casuarius casuarius) in North Queensland, Australia

2007

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We investigated the diet of the southern cassowary (Casuarius casuarius) by identifying the seeds and fruits in fecal droppings encountered on a set of transects over 2 yr in upland rain forest in the wet tropics of North Queensland. A total of 198 droppings containing 56 plant species were found. We surveyed fleshy fruit availability over the subsequent 68 mo on transects in the same area to ascertain fruiting patterns in the study area. The number of droppings found each month did not correspond to the pattern of available fruit biomass. There was no relationship between the fruit traits of moisture content, flesh to seed mass ratio, color, or crop size to contribution of a species to the diet. During the lean fruiting season (May–July) cassowaries relied more on species that fruited continuously throughout the year as they were significantly over‐represented in droppings, while annual fruiting species were under‐represented. During months of high fruit availability (October–December), continuously fruiting species were still over‐represented in the diet but became less important while annual and biennial species became more important. Significantly more species with large fruit and large seeds appeared in the diet than expected and we confirm that the cassowary contributes to the continued dispersal of these species over long distances and in large quantities.

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