Habitat loss and fragmentation affect the structure and functioning of forested ecosystems worldwide, yet we lack an understanding of how species respond to environmental changes. Here we examined reproductive success and seedling performance of Poulsenia armata (Moraceae) in continuous and fragmented forests of Los Tuxtlas, southern Mexico. We determined seed quality and seedling performance by combining isotopic analyses in seed quality with field observations on P. armata fruit production and a common garden experiment. If resources are less available for reproduction to relic parental trees of P. armatain fragments, we predicted: 1) small fruit crops, 2) low seed quantity and quality as reflected by seed mass, seed N and C content, and germination, and 3) low seedling performance (reduced survival and growth). We expected seedlings with low parental investment growing in forest fragments to allocate greater belowground biomass to compensate for the low seed N content. We further investigated how maternal source and soil conditions manifested in the seedling stage.
Soil conditions in forest fragments negatively impacted P. armata reproductive success. Trees of P. armata in forest fragments were smaller in size, produced fewer fruits and smaller seeds with lower quality compared to trees from the continuous forest. The combined effects of parental investment and soil conditions determined seedling survival and growth of this tropical tree. Notably, seedlings of this tree species had restricted plasticity for biomass allocation to roots, limiting the capacity of fragmented populations to compensate for the initial low N content in seeds. The observed seed quantity-quality trade-off to cope with poor soil conditions does not appear to be enough for successful recruitment of this species in forest fragments. Trees in forest fragments at Los Tuxtlas produced offspring competitively inferior and potentially less resilient than counterparts in continuous forest, jeopardizing the future persistence of P. armata in light of future global change.