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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

(A) Mean abundance and (B) mean dry mass of the three most abundant spiders at different distances from the margins of two streams during the wet and dry seasons.Filled bars, TPK; open bars, SM. Site abbreviations follow Fig. 1. Error bars, ±SEM. Note that the abundance scales and the dry mass scales differ between species and sites.
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fig-3: (A) Mean abundance and (B) mean dry mass of the three most abundant spiders at different distances from the margins of two streams during the wet and dry seasons.Filled bars, TPK; open bars, SM. Site abbreviations follow Fig. 1. Error bars, ±SEM. Note that the abundance scales and the dry mass scales differ between species and sites.

Mentions: A total of 865 individuals of 11 families of ground-dwelling spiders were collected along the transects at SM and TPK, 21–26% of which were captured along the 0 and 2-m transects (Fig. 2). Heteropoda venatoria (Sparassidae; n = 113, 13.1% of all spiders collected), Pardosa sumatrana (Lycosidae; n = 49, 5.7%) and Draconarius spp. (Agelenidae; n = 246, 28.4%) were the most abundant spiders together constituting 65% of the total number and 77% of the total biomass of all spiders collected within 2 m of the streams. Draconarius spp. were scarce along the stream margins (only 6–25% in terms of number, and 3–39% in terms of biomass of overall captures, Figs. 3A and 3B) relative to the two more inland transects at both sites and during both seasons. Heteropoda venatoria occurred along all four transects at both sites during both seasons (Fig. 3A). At TPK, the abundance of this spider appeared to be evenly distributed across the riparian zone during the wet season, but tended to increasing with distance from the stream during the dry season (Fig. 3A), although biomass was highest 2m from the stream during both seasons (Fig. 3B). At SM, abundance and biomass data suggested that H. venatoria was terrestrially-inclined or evenly distributed across the riparia (Figs. 3A and 3B). At both sites, this species maintained the highest biomass (4–28 mg/m2, Fig. 3B) of any spider, exceeding the total standing stock of all other species by 2–80 times. Pardosa sumatrana was found only within 2 m of the stream at both sites; its abundance and biomass were more than 10 times higher during the wet season (Figs. 3A and 3B). The abundance and biomass of P. sumatrana was also 13 times higher along the 0-m than the 2-m transect at TPK during the wet season, but they were similar along both transects at SM (Figs. 3A and 3B). Lycosidae (15.1% of the total), Salticidae (7.1%), Amaurobiidae (6.8%), Theridiidae, (6.2%), Gnaphosidae (6.0%), Linyphiidae (4.2%), Oecobiidae (3.5%), Corinnidae (2%), Pisauridae (1%) and Sparassidae (1%) constituted the remainder of the spiders.


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)

(A) Mean abundance and (B) mean dry mass of the three most abundant spiders at different distances from the margins of two streams during the wet and dry seasons.Filled bars, TPK; open bars, SM. Site abbreviations follow Fig. 1. Error bars, ±SEM. Note that the abundance scales and the dry mass scales differ between species and sites.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig-3: (A) Mean abundance and (B) mean dry mass of the three most abundant spiders at different distances from the margins of two streams during the wet and dry seasons.Filled bars, TPK; open bars, SM. Site abbreviations follow Fig. 1. Error bars, ±SEM. Note that the abundance scales and the dry mass scales differ between species and sites.
Mentions: A total of 865 individuals of 11 families of ground-dwelling spiders were collected along the transects at SM and TPK, 21–26% of which were captured along the 0 and 2-m transects (Fig. 2). Heteropoda venatoria (Sparassidae; n = 113, 13.1% of all spiders collected), Pardosa sumatrana (Lycosidae; n = 49, 5.7%) and Draconarius spp. (Agelenidae; n = 246, 28.4%) were the most abundant spiders together constituting 65% of the total number and 77% of the total biomass of all spiders collected within 2 m of the streams. Draconarius spp. were scarce along the stream margins (only 6–25% in terms of number, and 3–39% in terms of biomass of overall captures, Figs. 3A and 3B) relative to the two more inland transects at both sites and during both seasons. Heteropoda venatoria occurred along all four transects at both sites during both seasons (Fig. 3A). At TPK, the abundance of this spider appeared to be evenly distributed across the riparian zone during the wet season, but tended to increasing with distance from the stream during the dry season (Fig. 3A), although biomass was highest 2m from the stream during both seasons (Fig. 3B). At SM, abundance and biomass data suggested that H. venatoria was terrestrially-inclined or evenly distributed across the riparia (Figs. 3A and 3B). At both sites, this species maintained the highest biomass (4–28 mg/m2, Fig. 3B) of any spider, exceeding the total standing stock of all other species by 2–80 times. Pardosa sumatrana was found only within 2 m of the stream at both sites; its abundance and biomass were more than 10 times higher during the wet season (Figs. 3A and 3B). The abundance and biomass of P. sumatrana was also 13 times higher along the 0-m than the 2-m transect at TPK during the wet season, but they were similar along both transects at SM (Figs. 3A and 3B). Lycosidae (15.1% of the total), Salticidae (7.1%), Amaurobiidae (6.8%), Theridiidae, (6.2%), Gnaphosidae (6.0%), Linyphiidae (4.2%), Oecobiidae (3.5%), Corinnidae (2%), Pisauridae (1%) and Sparassidae (1%) constituted the remainder of the spiders.

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