Red crabs in rain forest, Christmas Island: removal and fate of fruits and seeds

1991 ◽  
Vol 7 (1) ◽  
pp. 113-122 ◽  
Author(s):  
Dennis J. O'Dowd ◽  
P. S. Lake
Keyword(s):  
Seed Predation ◽  
Rain Forest ◽  
Nitrogen Concentration ◽  
Oceanic Islands ◽  
Fruit Removal ◽  
Land Crab ◽  
Christmas Island ◽  
Direct Observations ◽  
Land Crabs ◽  
Seed Coats

ABSTRACTThe red land crab (Gecarcoidea nalalis) is the major collector of fruits and seeds from the rain forest Moor on Christmas Island, Indian Ocean. At three sites, they rapidly removed fruits and seeds of 17 species tested (usually within 12 h after placement) and most were taken to crab burrows. Direct observations of seed predation, and application of estimated chelar forces of red crabs indicated that seeds of many species, especially those with thin seed coats, are likely to be killed through handling. However, removal of some resistant seeds to burrows may be favourable for seedling establishment when canopy gaps occur. Fruit removal rates by crabs were positively related to nitrogen concentration in fruit tissues but negatively correlated with condensed tannins. These observations suggest that seed predation by land crabs may affect the success of colonization and the relative abundance of plants on oceanic islands.

Red crabs in rain forest, Christmas Island: removal and relocation of leaf-fall

1989 ◽  
Vol 5 (3) ◽  
pp. 337-348 ◽  
Author(s):  
Dennis J. O'Dowd ◽  
P. S. Lake
Keyword(s):  
Rain Forest ◽  
Forest Floor ◽  
Field Experiments ◽  
Single Species ◽  
Leaf Fall ◽  
Land Crab ◽  
Temporal And Spatial Patterns ◽  
Christmas Island ◽  
Temporal And Spatial ◽  
Gecarcoidea Natalis

ABSTRACTField experiments comparing leaf-fall in the presence and absence of the red land crab, Gecarcoidea natalis, in rain forest on Christmas Island, Indian Ocean showed that, by eating and returning leaves to their burrows, they significantly reduced accumulation of leaf-fall on the forest floor. Red crabs removed 30–50% of the leaf-fall at the experimental sites during the study. Differences in leaf-fall mass between crab-access and exclusion quadrats were positively correlated with the density of foraging red crabs. Red crabs also generated spatial heterogeneity in the distribution of litter on the forest floor by returning litter to their burrows. Leaves lined chambers of 64% of excavated burrows and litter biomass around the entrances was significantly greater than that on off-burrow locations. This was reflected in the significantly higher concentrations of organic matter and nutrients (N, P, K, Ca, Na, and Mg) associated with soils near burrow entrances. These results suggest that a single species, G. natalis, is the major processor of leaf-fall in rain forest on Christmas Island and may affect (1) the temporal and spatial patterns of nutrient availability and (2) the diversity and biomass of the litter fauna.

Effects of land crabs on seedling densities and distributions in a mainland neotropical rain forest

2002 ◽  
Vol 18 (1) ◽  
pp. 67-89 ◽  
Author(s):  
PETER MICHAEL SHERMAN
Keyword(s):  
Rain Forest ◽  
Land Crab ◽  
Diversity Gradient ◽  
The Pacific ◽  
Land Crabs ◽  
Dicotyledonous Plants ◽  
The Pacific Ocean ◽  
Neotropical Rain Forest ◽  
Corcovado National Park ◽  
Gecarcinus Quadratus

The land crab, Gecarcinus quadratus (Gecarcinidae), affects plant diversity in a mainland, neotropical rain forest through selective seedling consumption. In Costa Rica's Corcovado National Park, G. quadratus lives in fossorial populations with up to six crabs m−2 in coastal forest extending c. 600 m inland from the Pacific Ocean. A narrow transition zone (c. 30 m) separates the crab zone from the crabless zone that comprises the remainder of the 55 000-ha park. The composition of dicotyledonous plants from the adjacent zones were distinct: crabless zone transects (240 m2) contained 97 species representing 76 genera and 41 families; crab zone transects contained 46 species representing 38 genera and 25 families. Despite the narrow zonal separation, the crabless zone shared only 27.4, 29.9 and 52.8% of its species, genera and families, respectively, with the crab zone; in contrast, crab zone transects shared 56.5, 60.5 and 88% of their species, genera and families with the crabless zone. This abrupt diversity gradient suggests a powerful selection pressure in the crab zone preventing the establishment of certain dicotyledonous species. Two years of experimental crab exclusion suggested that G. quadratus reduces seedling density and diversity. Densities of seedlings (3–25 cm tall) within exclosures increased 144% over baseline values while control densities decreased. In contrast, seedlings at the cotyledon stage and taller (26–50 cm) were unaffected by crab exclusion. Preference tests conducted in the crab zone revealed a five-fold ratio of mortality rates for seedlings transplanted from the crabless zone and crab zone respectively. However, when protected from crabs, transplanted crabless and crab zone seedlings survived similarly well over 6 mo (83 and 70% respectively). Together, data from transects and experiments suggest that G. quadratus influences plant community composition.

The systematics of land crabs of the genus Gecarcoidea and recognition of a pseudocryptic species, G. humei, from the eastern Indian Ocean (Crustacea : Decapoda : Gecarcinidae)

2017 ◽  
Vol 31 (4) ◽  
pp. 406 ◽  
Author(s):  
Joelle C. Y. Lai ◽  
Hsi-Te Shih ◽  
Peter K. L. Ng
Keyword(s):  
Indian Ocean ◽  
Morphological Characters ◽  
Eastern Indian Ocean ◽  
Valid Species ◽  
West Pacific ◽  
Land Crab ◽  
Christmas Island ◽  
Extant Species ◽  
Land Crabs ◽  
The Family

The gecarcinid genus Gecarcoidea H. Milne Edwards, 1837 is currently represented by two species from the Indo-West Pacific – the widely distributed purple land crab, G. lalandii H. Milne Edwards, 1837, and the red crab endemic to Christmas Island, G. natalis (Pocock, 1889). One species, G. humei (Wood-Mason, 1874), described from the Nicobar Islands, has had a confused taxonomic history, but was treated as a junior synonym of G. lalandii by Türkay (1974) in his revision of the family. In this study, using molecular as well as morphological characters, we show that G. humei is a valid species. Gecarcoidea lalandii and G. humei have distinct non-overlapping distributions throughout much of their range, with G. lalandii occurring in most of South-east Asia and the West Pacific, while G. humei is known only from the eastern Indian Ocean. On Christmas Island, in the eastern Indian Ocean, however, all three species are present. As a result, Christmas Island is the only locality where all extant species of Gecarcoidea are found. The three species can also be separated by differences in live colours and patterns, as well as proportions of the carapace, male abdomen, ambulatory legs and third maxillipeds, and details of the orbits and male first gonopods.

Red Crabs in Rain Forest, Christmas Island: Differential Herbivory of Seedlings

Oikos ◽  
1990 ◽  
Vol 58 (3) ◽  
pp. 289 ◽  
Author(s):  
Dennis J. O'Dowd ◽  
P. S. Lake
Keyword(s):  
Rain Forest ◽  
Christmas Island
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