TY - JOUR
T1 - Supply-side ecology in mangroves
T2 - Do propagule dispersal and seedling establishment explain forest structure?
AU - Sousa, Wayne P.
AU - Kennedy, Peter G.
AU - Mitchell, Betsy J.
AU - Ordóñez L, Benjamín M.
PY - 2007/2
Y1 - 2007/2
N2 - Theory and empirical evidence suggest that spatial and temporal variation in propagule availability can have as great or greater an influence on community structure as post-recruitment biotic interactions, a phenomenon known as supply-side ecology. One of the first theories to invoke supply-side dynamics, D. Rabinowitz's Tidal Sorting Hypothesis (TSH), attributed the tidal zonation of mangrove tree species to the interacting effects of water depth and propagule size on dispersal and establishment. According to the TSH, smaller propagules are carried farther inland by flood tides than larger ones, stranding and establishing in greater numbers at upper tidal elevations. In contrast, larger propagules are better able to establish in deeper, more seaward areas because their size affords greater access to the soil surface and resistance to buffeting by moving water. Here we present results of the first comprehensive investigation of the TSH. In a series of experiments conducted at Punta Galeta on the Caribbean coast of Panama, we quantified patterns of propagule dispersal and establishment of the three dominant species: Avicennia germinans, Laguncularia racemosa, and Rhizophora mangle. To measure dispersal patterns, we monitored movements (directions and distances) of marked propagules released at three elevations along each of three transects. On all transects, regardless of species or elevation, propagules moved seaward rather than being carried inland by tides, as predicted by the TSH. Rates of seedling establishment were monitored in experiments conducted at different tidal elevations. Contrary to the TSH, all three species established best in the lower intertidal, where they were in prolonged contact with the soil surface during low tides, and established more poorly in the upper intertidal basin, where standing water made rooting difficult. Seedling establishment was lowest in the wave-exposed, back reef habitat, but in accordance with the TSH, the large propagules of Rhizophora rooted and persisted better in this turbulent habitat than did the smaller propagules of the other species. We conclude that the TSH does not explain the vertical distributions of mangrove species on Punta Galeta. Rather, a different form of supply-side dynamics imposed by the strong seaward movement of dispersing propagules is important in structuring our study forests.
AB - Theory and empirical evidence suggest that spatial and temporal variation in propagule availability can have as great or greater an influence on community structure as post-recruitment biotic interactions, a phenomenon known as supply-side ecology. One of the first theories to invoke supply-side dynamics, D. Rabinowitz's Tidal Sorting Hypothesis (TSH), attributed the tidal zonation of mangrove tree species to the interacting effects of water depth and propagule size on dispersal and establishment. According to the TSH, smaller propagules are carried farther inland by flood tides than larger ones, stranding and establishing in greater numbers at upper tidal elevations. In contrast, larger propagules are better able to establish in deeper, more seaward areas because their size affords greater access to the soil surface and resistance to buffeting by moving water. Here we present results of the first comprehensive investigation of the TSH. In a series of experiments conducted at Punta Galeta on the Caribbean coast of Panama, we quantified patterns of propagule dispersal and establishment of the three dominant species: Avicennia germinans, Laguncularia racemosa, and Rhizophora mangle. To measure dispersal patterns, we monitored movements (directions and distances) of marked propagules released at three elevations along each of three transects. On all transects, regardless of species or elevation, propagules moved seaward rather than being carried inland by tides, as predicted by the TSH. Rates of seedling establishment were monitored in experiments conducted at different tidal elevations. Contrary to the TSH, all three species established best in the lower intertidal, where they were in prolonged contact with the soil surface during low tides, and established more poorly in the upper intertidal basin, where standing water made rooting difficult. Seedling establishment was lowest in the wave-exposed, back reef habitat, but in accordance with the TSH, the large propagules of Rhizophora rooted and persisted better in this turbulent habitat than did the smaller propagules of the other species. We conclude that the TSH does not explain the vertical distributions of mangrove species on Punta Galeta. Rather, a different form of supply-side dynamics imposed by the strong seaward movement of dispersing propagules is important in structuring our study forests.
KW - Avicennia germinans
KW - Dispersal limitation
KW - Hydrochory
KW - Laguncularia racemosa
KW - Mangrove
KW - Propagule dispersal
KW - Rhizophora mangle
KW - Seedling establishment
KW - Supply-side ecology
KW - Tidal sorting hypothesis
KW - Tropical forests
KW - Zonation
UR - http://www.scopus.com/inward/record.url?scp=34247167921&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=34247167921&partnerID=8YFLogxK
U2 - 10.1890/05-1935
DO - 10.1890/05-1935
M3 - Article
AN - SCOPUS:34247167921
SN - 0012-9615
VL - 77
SP - 53
EP - 76
JO - Ecological Monographs
JF - Ecological Monographs
IS - 1
ER -