PATTERNS IN THE ORGANIZATION OF THE ARTHROPOD COMMUNITY ASSOCIATED WITH AN AUSTRALIAN RAINFOREST TREE: HOW DISTINCT FROM ELSEWHERE?

3 Pages·1993·0.09 MB·

by  Basset, Yves

Selbyana 14: 13-15
PATTERNS IN THE ORGANIZATION OF THE ARTHROPOD
COMMUNITY ASSOCIATED WITH AN AUSTRALIAN
RAINFOREST TREE: HOW DISTINCT FROM ELSEWHERE?
YVES BASSET
Bishop Museum, Department of Zoology, P.O. Box 19000A,
Honolulu, Hawaii 96817-0916
ABsTRACT. Several features of the arthropod community associated with an Australian rainforest tree,
Argyrodendron actinophyllum Edlin, are summarized. These include: taxonomic composition and its major
determinants; species richness and guild structure; arthropod seasonality and, in particular, the influence
ofleaf production on associated herbivores; spatial distribution of arthropods and ofleaf damage; species
diversity and body size relationships; synecology and aggregation pattems; and host specificity of associated
herbivores. Comparative data from similar arboreal communities are scarce but suggest that some of these
features may be similar in other communities, and others dissimilar. Tree species and overall rain forest
features may be responsible for these dissimilarities. Due to the extensive structural, phenological and
biochemical diversities ofr ainforest trees, arboreal communities are unlikely to follow a single, well-codified,
type of organization. However, it may be possible to recognize several types of arboreal communities by
considering the resource base on which the community is founded.
INTRODUCTION Work was performed at Mt. Glorious, near Bris
bane (details in Basset 1988, 1990). Canopyac
The study of arthropod faunas foraging within cess was provided by the single rope technique
rainforest canopies is still in its infancy. How of Perry (1978). Leaf production of A. actino
ever, it represents a growing field of interest in phyl/um appears to be synchronous among in
tropical entomology. To date, most of the pub dividuals but differs markedly between years for
lished information has been obtained using var fast-growing individuals and, therefore, does not
ious methods often ground-based, and only a appear to be highly predictable (Basset 1991a).
handful of studies have been performed in situ Foliar nutrients are low and chemical defenses
(e.g., Lowman 1985, Nadkami & Longino 1990). appear to be of the "quantitative" type (Basset
As a result, few studies go beyond the simple 1991 b). The arthropod fauna was collected using
description of taxonomic composition, species different sampling methods, which are detailed
richness and guild structure of the communities and discussed in Basset (1988, 1990).
of arboreal arthropods associated with rainforest
trees.
In this study, the arthropod fauna foraging
within the crowns of an overstory rainforest tree REsULTS AND DISCUSSION
in Australia, Argyrodendron actinophyl/um Ed Thanks to the information provided by more
lin, was studied in situ over a 4-year span. This than 50 taxonomists, who studied the arthropod
paper summarizes the information published on material, the major determinants of the taxo
this system and emphasizes the salient features nomic composition of the arboreal fauna asso
of the organization of the arthropod community. ciated with A. actinophyl/um could be identified
As far as possible, these features are contrasted (Basset 1991 c). These include: biogeographical
with the information available from other rain and historical constraints; rainforest mesocli
forest arthropod-tree systems. However, since mate and host phenology; host architecture and
comparative data are rather scarce, some more biochemistry; and intrinsic composition of the
speculative views are also expressed. Referencing foliage fauna. It is possible that other arthropod
has been kept to a minimum, for sake of brevity, tree systems in rain forests may be determined
and relevant references may be found in the pa in a similar way, but the relative contribution of
pers cited in the text. each of these factors is likely to be different.
The abundance of component taxa, species
richness and the guild structure ofthe arthropod
MATERIAL AND METHODS
community associated withA. actinophyl/um are
Argyrodendron actinophyl/um Edlin is a tall detailed in Basset and Arthington (1992). These
Sterculiaceae, up to 50 m tall. It is one of the data suggest that this arboreal community ex
dominant canopy species of the warm subtrop hibits several features common to arthropod
ical rain forests of Australia. Most of the field communities from temperate and tropical trees,
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14 SELBYANA [Volume 14
and point out the distinctness oft he system stud particular herbivore species, which may have very
ied. different behaviors and feeding strategies. Mines
The temporal organization of the arthropod were significantly more abundant in the lower
community is described in Basset (1991 a, 1991 d). croWD than in the upper crOWD. This type of
Most of the arthropod activity could be ex observation is also likely to depend on the for
plained primarily in terms of minimal air tem aging behavior of the dominant miner species,
peratures and leaf production events; less so by if any.
rainfall, relative humidity, or lunar phase. Sea When the relationships between the number
sonal ranges were significantly different among of species, the abundance of species and their
arboreal guilds and were related to food resource body size were considered (Basset & Kitching
availability in time. Seasonal peaks ofh erbivores 1991), it became apparent that a relatively high
were more marked than in the tropics but less proportion of rare and small species was repre
sharp than in temperate woodlands. Several phe sented in the samples. This concurs with several
nological features of the system could again be other rainforest studies (e.g., Erwin & Scott 1980,
classified under both tropical and temperate Morse et al. 1988, Barlow & Woiwod 1989). The
characteristics. The phenology ofleaf production biological meaning of these findings is not clear,
in Argyrodendron had also a pronounced effect and this may result in part from sampling arti
on the seasonality ofm ost herbivore species. Most facts.
herbivore activity occurred during windows of The cohesion of the arthropod community is
young foliage availability. Host suitability ofp ar appraised in Basset (1992c). Apparently, it was
ticular trees during study years depended upon not extremely strong. Although most arthropods
the intensity ofleafproduction and was different aggregated on the foliage, species associations
for specialist and generalist herbivores. Many were difficult to predict. Prey-predator ratios (ex
studies reported similar dependence of rainforest pressed as either number of individuals or spe
herbivores upon young foliage (e.g., Lowman cies) were relatively constant temporally but
1985, Aide & Londono 1989, Ernest 1989). highly variable spatially. It was concluded that
However, the strength of this relationship may this might be a consequence of both the unpre
ultimately depend on the relative palatibility of dictability ofleaf production and the overall high
young versus mature foliage. arthropod species-diversity in the rainforest en
The spatial distribution of arthropods within vironment. These observations, at the least, em
tree crowns is discussed in Basset (1991 b, 1992a, phasize that arboreal arthropod communities are
1992b). Most of the variance in arthropod dis not always organized into distinct component
tribution could be attributed to leaf age charac communities within the rainforest compound
teristics, arthropod aggregation patterns, arthro community (Basset 1993). However, at the mo
pod activity and distance to tree trunk. In contrast, ment, it is difficult to discuss the general validity
leaf size and foliage compactness were insignif of the data reported here.
icant in this regard. Arthropod stratification was Limited investigations about the diel activity
not well-marked within tree-crowns. Illumina ofa rthropods withirt the crowns of the study tree
tion patterns significantly influenced insect flight revealed that some herbivores were mostly ac
patterns inside tree crowns. The distribution and tive during night-time, possibly as a response to
the abundance of herbivores, and particularly day-active, visually oriented, predators (Basset
that of phloem-feeders, depended upon the ni & Springate 1992). This may represent a wide
trogen content of young leaves. The magnitude spread situation (Janzen 1983) but further testing
of leaf turnover affected both the quantity and of this hypothesis is required.
the quality ofy oung foliage available. Using path Lastly, little convincing evidence was found
analysis, it was shown that leaf turnover and that arthropods were closely associated, or host
translocation effects had a more direct influence specific, to A. actinophyllum. (Basset 19 92d). This
upon phloem-feeders than did total nitrogen. was tentatively explained by the low nutrient sta
Since nitrogen is a limiting factor for most insect tus of the host, its relative unpredictability of
herbivores, this situation may be similar for oth leaf production and the lack of strong predation
er insect-plant systems where the host is ever pressure on its foliage (particularly by arboreal
green and relatively low in foliar nutrients. ants). This situation is likely to be different for
Leaf damage and the presence of mines and other rainforest tree species, depending on their
galls on the foliage of A. actinophyllum was also biological features.
recorded and quantified (Basset 1991e). Appar
ently, leaf damage depended on the presence of
CONCLUSION
isolated, abundant and sunny patches of young
foliage. This is unlikely to be a general rule, since It was speculated that some of the features of
apparent damage is often influenced by a few the Argyrodendron community could be similar
1993] BASSET: ARTHROPOD COMMUNITY STRUCTURE 15
to other rainforest tree species and some others age, galls and mines within an Australian rainfor
dissimilar. Due to the extensive structural, phe est tree. Biotropica 23: 271-281.
nological and biochemical diversities ofrainfor ---. 1992a. Influence of leaf traits on the spatial
est trees, it is clear that arboreal communities distribution of arboreal arthropods within an
are unlikely to follow a single, well-codified, type overstorey rainforest tree. Ecological Entomology
17: 8-16.
of organization. However, Price (1992) empha
---. 1992b. Activite et distribution spatiale de
sized that the resource base on which a com a
l'entomofaune mobile associee un arbre des for
munity is founded can influence many aspects ets humides d'Australie. Vie et Milieu 42: 253-
of community organization and food web inter 262.
actions. He further advised to classifY resource --. 1992c. Synecology and aggregation patterns
types in order to detect patterns in nature. The of arboreal arthropods associated with an over
Argyrodendron community seems to be founded storey rainforest tree in Australia. Journal ofTrop
on a nutrient-poor resource, which is neverthe ical Ecology 8: 317-327.
less of the pUlsing type (see classification of re --. 1992d. Host specificity of arboreal and free
living insect herbivores in rain forests. Biological
source types in Price 1992). It would be partic
Journal of the Linnean Society 47: 115-133.
ularly interesting to detail patterns ofc ommunity
---. 1993. Arthropod species-diversity and com
organization (as attempted here for A. actino ponent communities in the rainforest canopy: les
phyllum) for an arboreal community associated sons from the study ofa n Australian tree. Tropical
with a nutrient-rich tree whose leaf production Zoology, Special Issue 1: 19-30.
is relatively constant and predictable (steadily --AND A. H. ARTHINGTON. 1992. The arthropod
renewed type of resource in Price 1992). community associated with an Australian rain
forest tree: abundance of component taxa, species
richness and guild structure. Australian Journal of
ACKNOWLEDGMENTS
Ecology 17: 89-98.
I thank R. L. Kitching and A. H. Arthington ---AND R. L. KITCHING. 1991. Species number,
for their support during the study and Neal Ev species abundance and body length of arboreal
arthropods associated with an Australian rainfor
enhuis for checking the manuscript. The study
est tree. Ecological Entomology 16: 391-402.
was funded by a predoctoral scholarship from
---AND N. D. SPRINGATE. 1992. Diel activity of
Griffith University. arboreal arthropods associated with a rainforest
tree. Journal of Natural History 26: 947-952.
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