Communities of Oribatida associated with litter input in western red cedar tree crowns: Are moss mats ‘magic carpets’ for oribatid dispersal? Zoë Lindo Department of Biology, University of Victoria, PO Box 3020, Victoria, British Columbia, V8W 3N5, Canada. Present address: Department of Biology, McGill University, 1205 Docteur Penfield, Montreal, Quebec, H3A 1B1, Canada. E-mail: [email protected]

Oribatid mite abundance, species richness, and community composition in annual litter fall were compared between the high canopy of an ancient temperate rainforest and the forest floor to evaluate whether litterfall, including moss debris, is a dispersal vector for these organisms. Oribatid were extracted from litterfall collected from canopy (30 m) and ground (1 m) litter traps associated with six western red cedar trees in the Walbran Valley on the south- west coast of Vancouver Island, Canada, over 3, 6, and 12 months. Total annual litter input was not significantly dif- ferent between canopy and ground traps, as high amounts of litter were associated with both habitats. Litter compo- sition differed between the two habitats and cumulative input over larger spatial scales may prove to be appreciably different. Fifty-seven species of oribatid mites were associated with total litterfall collected in canopy and ground traps over 12 months. Species richness over the entire sampling period was similar between canopy and ground habitats, but oribatid mite species composition differed significantly, and is most likely related to litter composition and the ini- tial source of litter. Oribatid mite abundance (number of individuals per gram dry weight) associated with litterfall was low compared to suspended soil habitats, and not significantly different between litter accumulation in ground and canopy traps. Nevertheless, a general trend of high litter input and high species richness associated with litterfall in canopy habitats, combined with high disperser survivorship, suggests dispersal vectors such as moss mats are impor- tant for maintaining arboreal oribatid mite communities.

Key words: Canopy, oribatid mites, litterfall, dispersal vector

n ancient western red cedar trees (Thuja plicata D. Don) to increase in abundance (Hubbell, 2001). In fragmented, I(Cupressaceae) of North American temperate rainforests, isolated, or patchily distributed habitats like suspended soils, suspended soils form high above the forest floor (ca. 35 m) I would expect dispersal to be especially limiting, and may and occur as discrete patches of habitat ranging in surface explain the arboreal specificity in forest oribatid mite com- area from 100 to 20,000 cm2 (Lindo & Winchester, 2006). munities. Suspended soils are habitat islands of accumulated organic The mechanism of oribatid mite colonization of canopy matter and epiphytes separated from one another within a habitats is unknown. Colonisation of canopy habitats by tree crown by a barren bark matrix and between trees by the ground-dwelling oribatid mites is unlikely based on ground/ atmosphere (Moffet, 2000). These habitats contain an abun- canopy comparison studies, and recently, the trunk has been dant and species-rich community of arboreal micro-arthro- dismissed as a potential dispersal corridor (Proctor et al., pods dominated by oribatid mites (Oribatida), many species 2002; Beaulieu et al., 2006; Lindo & Winchester, 2007b). A of which are undescribed and not found on the forest floor more parsimonious explanation is that canopy oribatid mites (Lindo & Winchester, 2006). Arboreal specificity in micro- colonize new canopy habitats from other canopy sources. communities and in particular oribatid mites has The proposed mechanisms of canopy-to-canopy dispersal been well documented (see Behan-Pelletier & Walter, 2000) include cursorial transport (Beaulieu et al., 2006), active and canopy/ground comparison studies show that the num- (Norton, 1980) and accidental (Krivolutsky & Lebedeva, ber of oribatid mite species in common between the two 2004a, b) phoresy, and aerial plankton (Karasawa et al., habitats is typically less than 40% (Wunderle, 1992a; Behan- 2005). Pelletier et al., 1993; Winchester et al., 1999; Lindo & Another possibility for aerial transport is via dispersal Winchester, 2006). Among the factors affecting the diversity vectors, such as moss and propagules, leaf litter, and abundance in arboreal oribatid mite communities are branch tips, and twigs. The importance of a particular vector tree species, elevation (Fagan et al., 2005), and the availabil- depends on the rate at which dispersers are carried to a ity of habitat (Lindo & Winchester, 2007a). Dispersal events, recipient habitat (propagule load) and on the survivorship colonization history, local and regional scale structural com- during transport. Dispersal vectors could have high propag- plexity, and stability of suspended soil environments are also ule loadings and high survivorship of dispersers due to less- hypothesised as major determinants of arboreal oribatid er changes in environmental conditions during transport. mite species richness (Southwood, 1996). There is limited evidence for such a passive dispersal mech- Dispersal is a dynamic biological process that is a driver anism in arboreal oribatid mites (Wunderle, 1992b; Karasa- of many ecological theories such as island biogeography wa et al., 2005), but horizontal movement within canopy sys- (MacArthur & Wilson, 1967), metapopulation (Hanski, 1999) tems is probable, as is transport to lower canopy habitats or and metacommunity dynamics (Wilson, 1992), and neutral the forest floor by litterfall. models (Bell, 2000; Hubbell, 2001; Chave et al., 2002). Under The degree to which dispersal and dispersal limitations low rates of dispersal, species are more aggregated, and contribute to the dynamics and structure of communities rare, local, or endemic species can survive in high abundance advocates the need to elucidate the mechanisms of disper- because of lack of competitors and adequate ecological time sal, to quantify dispersal rates, as well as to quantify the spa-

Trends in Acarology [2009] M.W. Sabelis & J. Bruin (eds.) 143 Zoë Lindo

Table 1 Results of repeated measures ANOVA for oribatid mite species richness (average number species per trap), and abundance of micro- (total number individuals per g dwt litter; mean ± SD) collected in litter traps at 30 m and 1 m above the forest floor associated with six western red cedar trees after 12 months. Given are P-values for different sources of variation with degrees of freedom in parenthe- ses. Canopy (30 m) Ground (1 m) Habitat (1,10) Time (2,20) Time × Habitat (2,20) Oribatida species richness 19.17 ± 2.8 13.50 ± 5.1 0.007 <0.001 <0.001 Oribatida abundance 0.542 ± 0.32 0.506 ± 0.20 0.123 0.482 0.038 abundance 0.249 ± 0.09 0.224 ± 0.32 0.701 0.001 0.923 abundance 0.082 ± 0.05 0.095 ± 0.17 0.686 0.260 0.125 Collembola abundance 10.407 ± 11.51 1.562 ± 0.60 0.096 0.039 0.069 Other micro-arthropod abundance 0.195 ± 0.28 0.139 ± 0.04 0.435 0.038 0.297 Total micro-arthropod abundance 11.475 ± 11.38 2.527 ± 0.86 0.234 0.044 0.152 tial scale in which dispersal occurs. The objectives of this I used repeated measures ANOVA to test for the effect of study were: (1) measure and compare annual amounts of lit- time and habitat on litter input in canopy and ground litter ter input into canopy and ground habitats, and (2) observe traps, abundance of major micro-arthropod groups, and ori- oribatid mite species and abundances associated with annu- batid mite species richness. These analyses were performed al litter input in these two habitats to evaluate whether lit- using Statistica 7.0 (StatSoft Inc., 2004) with a significance terfall is a dispersal vector for these organisms. level of α = 0.05. Community composition of adult oribatid mites in canopy- and ground-collected litterfall was evaluat- ed using non-metric multidimensional scaling (NMDS) MATERIALS AND METHODS (Clarke, 1993) which arranged the samples (traps) with The study site was located in the temperate rainforest of the respect to the rank order of similarity in community compo- Walbran Valley on the southwest coast of Vancouver Island, sition based on Bray-Curtis similarity of √x-transformed orib- British Columbia, Canada (48°39’N, 124°35’W). The valley atid mite species abundance data. The final ordination of a lies entirely within the CWH biogeoclimatic zone (Meidinger priori trap placement was assessed for significance of ran- & Pojar, 1991) where the climate is characterized by wet, dom occurrence based on analysis of similarities (ANOSIM) humid, cool summers and mild winters, and where a mean with 10,000 randomized permutations using habitat (30 m annual precipitation of 2,990 mm is typical for this area canopy, 1 m ground) and collection time (3, 6, 12 months) as (Environment Canada, 2006). Conifers are dominant in this factors (Primer, 2001). rainforest and include western hemlock (Tsuga heterophylla (Rafn.) Sarg.), Sitka spruce (Picea sitchensis (Bong) Carr.), Amabilis fir (Abies amabilis (Dougl.) Forb.), and western red RESULTS cedar (Thuja plicata D. Don). The six western red cedar trees Total amount of litterfall over 12 months in canopy vs. ground used in this study were approximately 50 m tall, with the traps was not statistically different (F1,10 = 3.079, P = 0.110), diameter of the trunks at breast height ranging from 2.13 to although litterfall was consistently higher in canopy litter traps 3.65 m (mean ± SD = 2.71 ± 0.52 m). These trees are estimat- (Fig. 1). There was a significant effect of time on amount of lit- ed to be 800-1,200 years old, and well developed suspended terfall collected, with the most litterfall collected between 3 2 soils ranging in size from 0.1 to 2.0 m are abundant within and 6 months (F2,20 = 14.212, P<0.001). Litterfall primarily con- tree crowns at heights greater than 20 m where trunk reiter- sisted of moss, cedar bark, litter and twigs, hemlock cones and ations and major limb junctions take place. needles, and herbaceous litter. Differences in litterfall Single rope climbing techniques were used to access tree composition were observed between canopy and ground with crowns. Litter traps constructed of grain feed bags sewn to litter accumulation in canopy traps predominated by moss 12-gauge wire hoops (surface area = 0.25 m2, depth = 30 cm) and cedar derivatives, whereas ground traps accumulated lit- (Hughes et al., 1987) were secured in the canopy at 30 m. ter primarily from hemlock sources. Litter traps were secured in freestanding space by three Average oribatid mite, other , and total micro- attachment points to neighbouring limbs or trunks within arthropod abundance was low, and the total number of indi- each western red cedar tree crown. Litter traps were also placed 1 m above the forest floor, 1.5 m from the base of each tree on the north side. Ground litter traps were sup- 240 ported at three attachment points to the wire hoop using 210 Canopy (30m)

PVC legs (2 cm in diameter, 110 cm long) inserted 10 cm into ) 2 180 the forest floor. Litter traps were installed in June 2005 and Ground (1m) litterfall was collected after 3, 6, and 12 months. 150 Micro-arthropods were extracted from total litter accu- 120 mulations after each collection date into 70% EtOH using 90 modified Berlese funnels over 48 h (Norton & Kethley, 1988). (g dwtper 0.25 m 60 Cumulative litter input Abundance data is calculated as number of individuals per 30 gram dry weight and is used for comparisons with indige- 0 nous suspended soil-dwelling oribatid mite communities. 3 months 6 months 12 months Extracted micro-arthropods were sorted into Acari, Time in field Collembola, and others. Acari were further identified to sub- Figure 1 Cumulative litter input (mean ± SD) in canopy (30 m) and order (Mesostigmata, Prostigmata, Oribatida), and all adult ground (1 m) litter traps (surface area = 0.25 m2) over 3, 6, and 12 oribatid mites were identified to species. months associated with western red cedar trees in temperate rain- forest in the Walbran Valley on Vancouver Island, BC, Canada.

144 Are moss mats ‘magic carpets’ for oribatid mite dispersal?

Table 2 Oribatid mite species (Acari: Oribatida) abundances from litterfall in canopy (30 m) and ground (1 m) litter traps associated with western red cedar trees in the Walbran Valley, Vancouver Island, BC, Canada. Family Species Canopy Ground Liochthonius sp. 1 0 2 Liochthonius sp. 2 3 1 Liochthonius sp. 4* 0 1 Archiphthiracarus sp. 28 4 Maerkelotritia sp. nr. alaskensis Hammer 1967 25 2 Mesotritia nuda (Berlese 1887) 9 0 Euphthiracarus cernuus Walker 1965 3 0 Euphthiracarus monyx Walker 1965 1 0 Epilohmanniidae Epilohmannia sp. 7 2 Camisia segnis (Hermann 1804) 1 11 Platynothrus sp. nr. peltifer (C.L. Koch 1839) 0 4 Trhypochthoniidae Trhypochthonius tectorum (Berlese 1896) 10 0 Hermaniellidae Hermanniella sp. nr. occidentalis Ewing 1918 0 1 Platyliodes macroprionus Woolley & Higgins 1969 1 5 Gymnodamaeus sp. 1 0 (Belba) sp. 4 0 Epidamaeus sp. nr. floccosus Behan-Pelletier & Norton 1985 7 0 Cepheus corae Jacot 1928 0 2 Eupterotegaeus rhamphosus Higgins & Woolley 1963 8 1 Eupterotegaeus sp. nr. rostratus Higgins & Woolley 1963 30 5 Ommatocepheus sp. 0 6 Caleremaeidae Caleremaeus sp. 2 1 Eremaeidae Eueremaeus acostulatus Behan-Pelletier 1993 1 0 Eueremaeus chiatous (Higgins 1979) 7 2 Eueremaeus marshalli Behan-Pelletier 1993 20 0 Megeremaeus montanus Higgins & Woolley 1965 0 1 Dorycranosus sp. 1 1 Liacarus sp. nr. bidentatus Ewing 1918 0 9 Liacarus sp. nr. robustus (Gervais 1844) 1 0 Peloppiidae Ceratoppia sp. 1 0 3 Ceratoppia sp. 2 7 11 Ceratoppia sp. 3 2 3 Dendrozetes sp. 2 14 Metrioppia sp. 0 1 Parapyroppia lamellata (Ewing 1909) 0 1 Kodiakellidae Kodiakella lutea Hammer 1967 5 1 Tectocepheidae Tectocepheus velatus (Michael 1880) 4 1 Oppiidae Oppiella sp. 2* 0 2 Quadroppiidae Quadroppia quadricarinata (Michael 1885) 4 1 Suctobelbidae Suctobelbella sp. nr. longicuspis Jacot 1937 0 1 Suctobelbella sp. 7* 1 0 Autognetidae Autogneta sp. nr. longilamellata (Michael 1885) 0 1 Scapheremaeus palustris (Sellnick 1924) 6 12 Achipteria sp. nr. curta Aoki 1970 0 1 Anachipteria acuta (Ewing 1918) 10 1 Dentachipteria sp. 2 1 Parapirnodus coniferinus Behan-Pelletier et al. 2002 2 0 Parapirnodus hexaporosus Behan-Pelletier et al. 2002 4 2 Scheloribates (Scheloribates) sp. 20 12 Scheloribates (Hemileius) sp. 1 0 sp. 24 30 Oribatellidae Oribatella sp. 0 1 Ceratozetes pacificus Behan-Pelletier 1984 1 0 winchesteri Behan-Pelletier 2000 14 0 Trichoribates sp. 0 2 Mycobatidae Mycobates corticeus Behan-Pelletier 2001 31 1 Pilogalumna sp. 8 1 Total abundance 318 165 *species are numbered to be consistent with Lindo & Winchester (2006). Numbers for each species are numbers of specimens collected within each habitat. viduals collected over the 12 months was not significantly Total oribatid mite species richness recorded over the entire different between trap heights when standardized on a num- sampling period was similar for canopy (40 species) and ber/g dwt basis (Table 1). A total of 57 oribatid mite species ground (42 species) habitats. The average number of species were identified from 483 adult specimens (318 canopy, 165 collected per trap was significantly greater in the canopy ground) collected from all traps over 12 months (Table 2). compared to the ground traps (Table 1). The composition of

145 Zoë Lindo oribatid mite species collected in 30 m and 1 m traps over The distinction between active and passive dispersal is the 12 months, differed significantly based on Bray-Curtis important as the two processes have different consequences percent similarity in NMDS ordination (ANOSIM: Global R = for colonisation events, population dynamics, and communi- 0.577, P = 0.001) (Fig. 2). There was also a significant effect ty structure, particularly in a patchy habitat (Bowman et al., of collection date, with communities collected at 3, 6, and 12 2002). Beaulieu et al. (2006) found cursorial mesostigmatic months (September, January, and June, respectively) being mite dispersal across corticolous habitats within the canopy significantly different from one another in pair wise tests and between canopy habitat patches in arboreal mesostig- (ANOSIM: Global R = 0.595, P = 0.001). The most abundant matic mite communities. Generally oribatid mite abundance species found in canopy traps were (Table 2) Mycobates cor- is low in corticolous habitats, however, while bark is a more ticeus, Eupterotegeus sp. nr. rostratus, Archphthiracarus sp., extreme environment for oribatid mites than either soil or Maerkelotritia sp. nr. alaskensis, and Phauloppia sp., which suspended soil habitats, compensatory redistribution among accounted for nearly 50% of individuals collected in litterfall microhabitats on exposed bark may enable mites to main- at 30 m. In 1 m ground traps 50% of individuals collected tain viable moisture and temperature requirements during were Phauloppia sp., Dendrozetes sp., Scheloribates (Schel- cursorial transport (Prinzing, 2005). However, rates of active oribates) sp., Scapheremaeus palustris, and Camisia segnis. cursorial transport are low for most species of oribatid mites (Berthet, 1964; Wunderle, 1992b; Ojala & Huhta, 2001). Oribatid mites, unlike their prostigmatic and mesostigmatic DISCUSSION relations, are typically not known to participate actively in Canopy research has increased in the last few decades, and phoresy (with exceptions, e.g., Mesoplophora sp.; see with this research has come a greater appreciation for the Norton, 1980), but ‘accidental’ phoresy may occur as there is interaction of above- and below-ground processes (Wardle, evidence for transport on birds (Krivolutsky & Lebedeva, 2002; DeDeyn & van der Putten, 2005). This study shows 2004a, b). Transport by wind as aerial plankton (anemo- high amounts of litterfall are produced and circulate chory) has long been suggested though documentation of throughout the year within canopy habitats, with only a frac- this is scant (Karasawa et al., 2005). Long-distance dispersal tion of that litter entering forest floor systems. Values of on air currents is possible and probable due to the small size annual litterfall in the ground traps are similar to other old- of mites, and therefore individuals might also be carried con- growth temperate rainforests in Washington State (USA) siderable distances (Jung & Croft, 2001; Griffin et al., 2002), (Edmonds & Murray, 2002), and interior forests of British although there is often a low probability of dispersal success Columbia (Canada) (Thomas & Prescott, 2000; Welke et al., due to desiccation (Mitchell, 1970). 2005). Although the difference between litter input to forest Colonisation history, structural complexity, and environ- floor and canopy systems was not statistically significant on mental stability are all major determinants of species rich- the small spatial scale observed, annual litter input scaled ness (Southwood, 1996; Fagan et al., 2005). There was high over larger areas suggests considerable differences (canopy species richness of oribatid mites recorded from litterfall in = 5,754.8 kg/ha, ground = 3,452.4 kg/ha). I acknowledge that canopy and ground litter traps although relatively few indi- litter traps used in this study may overestimate the amount viduals were collected. Abundance of individuals was gener- of litter actually retained within the canopy because of the ally low compared to abundances present in forest floor or conical shape of the traps used. It should be noted however, suspended soils (Lindo & Winchester, 2006) but are compa- that tree crown architecture in ancient western red cedar rable to corticolous cedar habitats (Lindo & Winchester, trees at this study site provide similarly shaped catchment 2007b), and greater than the 17 species of oribatid mites col- areas. Tree crown and overall canopy architectural complex- lected from litterfall in beech forests of Germany (Wunderle, ity is important in capturing and retaining litter within tree 1992b). The high species diversity associated with the large crowns, and most likely increases the capture and retention amount of litterfall into canopy habitats suggests dispersal of micro-arthropods in the canopy (Sillett & Bailey, 2003). vectors may be important in contributing to rescue effects in patchily distributed habitats like suspended soils (Brown & Kodric-Brown, 1977). Oribatid mite dispersal via dispersal vectors such as moss mats is probably more likely to supple- Stress: 0.16 ment existing canopy populations than phoresy or aerial plankton mechanisms (Wunderle, 1992b). Coulson et al. Canopy (2002) suggest dispersal vectors may even enhance survival of trans-oceanic dispersal of terrestrial soil-dwelling arthro- pods. Aerial transport within organic matter substrate could

Dimension 2 protect against desiccation and ensure organisms arrive at a new destination alive. The method of active extraction to Ground collect oribatid mites from the litterfall demonstrates that organisms were alive in collected litterfall, and suggests they are able to survive transport within dispersal vectors to a Dimension 1 new habitat patch. Canopy and ground litter-associated species richness Figure 2 Non-metric multidimensional scaling (NMDS) plot of orib- over the entire collection period was similar, though the atid mite communities associated with total litterfall in three collec- tion times over 12 months from canopy (30 m) and ground (1 m) lit- composition of the two communities was not. The number ter traps associated with western red cedar trees on Vancouver of species shared between canopy and ground traps (23 out Island, Canada. Ordination produced from Bray-Curtis similarity of 57 species total) is the same percentage typically found in matrix of mean standardized (number individuals per 100 g dwt lit- canopy/ground comparison studies (40%) (Wunderle, terfall) species abundances. Stress value = 0.16 indicates data con- 1992a; Behan-Pelletier et al., 1993; Winchester et al., 1999; form well within defined dimensions.

146 Are moss mats ‘magic carpets’ for oribatid mite dispersal?

Lindo & Winchester, 2006). However, while ground traps Bell G (2000) The distribution of abundance in neutral communities. were composed of different species compared to canopy Am Nat 155: 606-617. traps, the ground traps did not consist of ground species, but Berthet PL (1964) Field study of the mobility of Oribatei (Acari), rather canopy species associated with other tree species. using radioactive tagging. J Anim Ecol 33: 443-449. Brown JH& Kodric-Brown A (1977) Turnover rates in insular biogeog- The influence of other tree species was apparent when com- raphy: effect of immigration on extinction. Ecol 58: 445-449. paring litter composition and the species associated with the Bowman J, Cappuccino N & Fahrig L (2002) Patch size and popula- litterfall in canopy vs. ground traps. The higher incidence of tion density: the effect of immigration behaviour. Cons Ecol 6 p9. hemlock needles, cones, and branches in ground traps corre- http: //www.consecol.org/vol6/iss1/art9/ Cited 4 Aug 2006. sponded with species composition of oribatid mites known Cadotte MW & Fukami T (2005) Dispersal, spatial scale and species from previous hemlock canopy studies. Dendrozetes, diversity in a hierarchically structured experimental landscape. Scapheremaeus, and Camisia are genera observed from Ecol Letters 8: 548-557. canopy studies where hemlock is the focal tree (Winchester Chave J, Mullen-Landau HC & Levin SA (2002) Comparing classic community models: theoretical consequences for patterns of et al., 2008), and not found in suspended soils of western red diversity. Am Nat 159: 1-23. cedar (Lindo & Winchester, 2006). Clark JS (1998) Why trees migrate so fast: confronting theory with Horizontal movement of oribatid mites within canopy dispersal biology and the paleorecord. 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