Ecological Archives E084-018-A1

Emilio M. Bruna.  2003.  Are plant populations in fragmented habitats recruitment limited? Tests with an Amazonian herb. Ecology 84:932–947.

Appendix A. Calculation of per-individual fecundity (Fi) for transition matrices.

Per-individual fecundity (Fi) was calculated as: , where pi = the probability of flowering by plants in each stage class in each location, s = the number of seeds per fruit, f= the number of fruits produced per flowering plant, and g = probability of seed germination and seedling establishment.  Median fruit set in annual surveys was not significantly different in 1-ha fragments, 10-ha fragments, or continuous forest for either of the two survey years (Bruna and Kress 2002), and there is no evidence that seed set varies systematically with habitat type or plant size.  I therefore set fi = 4 (the median value from 348 fruiting plants recorded during the 1998 and 1999 flowering seasons) and s = 2 (mean seeds per fruit = 1.9 ± 0.02 SE, median = 2, n = 873 fruits) for all calculations of Fi.  However, annual surveys did reveal substantial variation among plots in the number of flowering plants (total n = 466) and the proportion of plants in each stage class flowering (Bruna and Kress 2002) , therefore calculations of Fi for each demographic plot used the specific values of pi observed in that location (Bruna 2001).  Values of g were experimentally derived.  Here I briefly describe these experiments. Detailed descriptions have been published elsewhere (Bruna 1999, 2002). 

I planted H. acuminata seeds along five 100-m transects in areas immediately adjacent to the ten demographic plots established in 1998.  Seeds were planted in three experimental treatments designed to give increasing levels of protection to seeds: directly on the ground (mimicking natural dispersal and exposure to agents of seedling mortality), in an open plastic cup (preventing removal of seeds but allowing the accumulation of leaf litter and soil), and in a cup but covered with a fine mesh (to prevent all seed predation as well as leaf litter accumulation).  I surveyed these seeds for one year, recording the proportion of seeds germinating and establishing as seedlings.  These experiments were repeated twice: once for the 1998–1999 transition year (n = 1668 seeds) and once for the 1999–2000 transition year (n = 1320 seeds).  Since I was interested in projecting under natural conditions of seed germination and seedling establishment, I used the estimates of germination from the experimental treatment mimicking natural conditions in all calculations of Fi (referred to as the “ground” treatment in Bruna 1999 and Bruna 2001).  No direct estimates of seed germination existed for the three continuous forest sites established in 1999 (CF 4-6), I therefore used the averages of results from the three other continuous forest sites. 

Literature Cited

Bruna, E. M. 1999. Seed germination in rainforest fragments. Nature 402:139.

Bruna, E. M. 2001. Effect of habitat fragmentation on the reproduction and population dynamics of an Amazonian understory herb (Heliconia acuminata, Heliconiaceae). Thesis. University of California, Davis, California, USA.

Bruna, E. M. 2002. Effects of forest fragmentation on Heliconia acuminata seedling recruitment in central Amazonia. Oecologia 132:235–243.

Bruna, E. M., and W. J. Kress. 2002.  Habitat fragmentation and the demographic structure of an Amazonian understory herb (Heliconia acuminata). Conservation Biology, in press.

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