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Spatio-temporal variability in the distribution of ground-dwelling riparian spiders and their potential role in water-to-land energy transfer along Hong Kong forest streams.

Yuen EY, Dudgeon D - PeerJ (2015)

Bottom Line: Circumstantial evidence supports this notion, as P. sumatrana was virtually absent during the dry season when aquatic insect emergence was low.In general, forest-stream riparia in Hong Kong did not appear to be feeding hotspots for ground-dwelling predators.The biomass and inland distribution of H. venatoria could make it a likely conduit for the stream-to-land transfer of energy.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Biological Sciences, The University of Hong Kong , Hong Kong SAR , People's Republic of China.

ABSTRACT
Terrestrial predators have been shown to aggregate along stream margins during periods when the emergence of adult aquatic insects is high. Such aggregation may be especially evident when terrestrial surroundings are relatively unproductive, and there are steep productivity gradients across riparia. In tropical forests, however, the productivity of inland terrestrial habitats may decrease the resource gradient across riparia, thus lessening any tendency of terrestrial predators to aggregate along stream margins. We elucidated the spatio-temporal variability in the distribution of ground-dwelling spiders and terrestrial arthropod prey within the riparia of two forest streams in tropical Hong Kong by sampling arthropods along transects at different distances from the streams during the wet and dry seasons. Environmental variables that may have influenced spider distributions were also measured. The vast majority of ground-dwelling predators along all transects at both sites were spiders. Of the three most abundant spiders captured along stream margins, Heteropoda venatoria (Sparassidae) and Draconarius spp. (Agelenidae) were terrestrially inclined and abundant during both seasons. Only Pardosa sumatrana (Lycosidae) showed some degree of aggregation at the stream banks, indicating a potential reliance on aquatic insect prey. Circumstantial evidence supports this notion, as P. sumatrana was virtually absent during the dry season when aquatic insect emergence was low. In general, forest-stream riparia in Hong Kong did not appear to be feeding hotspots for ground-dwelling predators. The lack of aggregation in ground-dwelling spiders in general may be attributed to the low rates of emergence of aquatic insects from the study streams compared to counterpart systems, as well as the potentially high availability of terrestrial insect prey in the surrounding forest. Heteropoda venatoria, the largest of the three spiders maintained a high biomass (up to 28 mg dry weight/m(2)) in stream riparia, exceeding the total standing stock of all other spiders by 2-80 times. The biomass and inland distribution of H. venatoria could make it a likely conduit for the stream-to-land transfer of energy.

No MeSH data available.


Related in: MedlinePlus

Locations of the two study reaches in Tai Po Kau Forest Stream (TPK) and Lead Mine Pass Stream (SM).
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fig-1: Locations of the two study reaches in Tai Po Kau Forest Stream (TPK) and Lead Mine Pass Stream (SM).

Mentions: The study reaches were along Tai Po Kau Forest Stream (TPK: 3rd order; 22°25′24″N, 114°10′48″E) and along Lead Mine Pass Stream (SM: 4th order; 22°23′51″N, 114°09′05″E) in Hong Kong, southern China (Fig. 1). They were two of the three sites used in our concurrent investigation of spider stable-isotope signatures (Yuen & Dudgeon, in press). Both were unpolluted hill streams situated in drainage basins dominated by secondary forest (>60 years regrowth) within protected areas established in the 1970s (Dudgeon & Corlett, 2011). The streams were thus well protected from human disturbance. The study reaches were situated at ∼200 m a.s.l. and were similar in terms of wet width (∼8 m during the wet season; ∼3.5 m during the dry season), depth (riffles: ∼0.5 m during the wet season; 0.3 m during the dry season; pools >1 m during both seasons), streambed substrate type (dominated by cobbles in riffles, gravels in slow-flowing regions) and canopy coverage (>80%) (Table 1). Sampling was undertaken along one 50-m section of bank adjacent to each reach. At SM the eastern bank was selected as it was gently-sloping (<10° at 0–6 m from the stream and up to 15° further inland), comprising a 2–6 m-wide accumulation of gravel bordered by dense clumps of Acorus gramineus (Acoraceae) at the stream margin and secondary forest inland, where common trees included Syzygium jambos (Myrtaceae), Schefflera heptaphylla (Araliaceae), Pavetta hongkongensis (Rubiaceae). The western stream bank at TPK had a steeper gradient (<10°within 3 m of the stream, and up to 30° further inland), consisting of small, narrow gravel patches (2–10 m long, 1–3 m wide) and large boulders (up to 1 m in diameter) interspersed by secondary forest mainly consisting of Aporusa dioica (Euphorbiaceae), Rhodoleia championi (Hameamelidaceae) and Garcinia oblongifolia (Guttiferae).


Spatio-temporal variability in the distribution of ground-dwelling riparian spiders and their potential role in water-to-land energy transfer along Hong Kong forest streams.

Yuen EY, Dudgeon D - PeerJ (2015)

Locations of the two study reaches in Tai Po Kau Forest Stream (TPK) and Lead Mine Pass Stream (SM).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4525688&req=5

fig-1: Locations of the two study reaches in Tai Po Kau Forest Stream (TPK) and Lead Mine Pass Stream (SM).
Mentions: The study reaches were along Tai Po Kau Forest Stream (TPK: 3rd order; 22°25′24″N, 114°10′48″E) and along Lead Mine Pass Stream (SM: 4th order; 22°23′51″N, 114°09′05″E) in Hong Kong, southern China (Fig. 1). They were two of the three sites used in our concurrent investigation of spider stable-isotope signatures (Yuen & Dudgeon, in press). Both were unpolluted hill streams situated in drainage basins dominated by secondary forest (>60 years regrowth) within protected areas established in the 1970s (Dudgeon & Corlett, 2011). The streams were thus well protected from human disturbance. The study reaches were situated at ∼200 m a.s.l. and were similar in terms of wet width (∼8 m during the wet season; ∼3.5 m during the dry season), depth (riffles: ∼0.5 m during the wet season; 0.3 m during the dry season; pools >1 m during both seasons), streambed substrate type (dominated by cobbles in riffles, gravels in slow-flowing regions) and canopy coverage (>80%) (Table 1). Sampling was undertaken along one 50-m section of bank adjacent to each reach. At SM the eastern bank was selected as it was gently-sloping (<10° at 0–6 m from the stream and up to 15° further inland), comprising a 2–6 m-wide accumulation of gravel bordered by dense clumps of Acorus gramineus (Acoraceae) at the stream margin and secondary forest inland, where common trees included Syzygium jambos (Myrtaceae), Schefflera heptaphylla (Araliaceae), Pavetta hongkongensis (Rubiaceae). The western stream bank at TPK had a steeper gradient (<10°within 3 m of the stream, and up to 30° further inland), consisting of small, narrow gravel patches (2–10 m long, 1–3 m wide) and large boulders (up to 1 m in diameter) interspersed by secondary forest mainly consisting of Aporusa dioica (Euphorbiaceae), Rhodoleia championi (Hameamelidaceae) and Garcinia oblongifolia (Guttiferae).

Bottom Line: Circumstantial evidence supports this notion, as P. sumatrana was virtually absent during the dry season when aquatic insect emergence was low.In general, forest-stream riparia in Hong Kong did not appear to be feeding hotspots for ground-dwelling predators.The biomass and inland distribution of H. venatoria could make it a likely conduit for the stream-to-land transfer of energy.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Biological Sciences, The University of Hong Kong , Hong Kong SAR , People's Republic of China.

ABSTRACT
Terrestrial predators have been shown to aggregate along stream margins during periods when the emergence of adult aquatic insects is high. Such aggregation may be especially evident when terrestrial surroundings are relatively unproductive, and there are steep productivity gradients across riparia. In tropical forests, however, the productivity of inland terrestrial habitats may decrease the resource gradient across riparia, thus lessening any tendency of terrestrial predators to aggregate along stream margins. We elucidated the spatio-temporal variability in the distribution of ground-dwelling spiders and terrestrial arthropod prey within the riparia of two forest streams in tropical Hong Kong by sampling arthropods along transects at different distances from the streams during the wet and dry seasons. Environmental variables that may have influenced spider distributions were also measured. The vast majority of ground-dwelling predators along all transects at both sites were spiders. Of the three most abundant spiders captured along stream margins, Heteropoda venatoria (Sparassidae) and Draconarius spp. (Agelenidae) were terrestrially inclined and abundant during both seasons. Only Pardosa sumatrana (Lycosidae) showed some degree of aggregation at the stream banks, indicating a potential reliance on aquatic insect prey. Circumstantial evidence supports this notion, as P. sumatrana was virtually absent during the dry season when aquatic insect emergence was low. In general, forest-stream riparia in Hong Kong did not appear to be feeding hotspots for ground-dwelling predators. The lack of aggregation in ground-dwelling spiders in general may be attributed to the low rates of emergence of aquatic insects from the study streams compared to counterpart systems, as well as the potentially high availability of terrestrial insect prey in the surrounding forest. Heteropoda venatoria, the largest of the three spiders maintained a high biomass (up to 28 mg dry weight/m(2)) in stream riparia, exceeding the total standing stock of all other spiders by 2-80 times. The biomass and inland distribution of H. venatoria could make it a likely conduit for the stream-to-land transfer of energy.

No MeSH data available.


Related in: MedlinePlus