When sex is not enough: ecological correlates of resprouting capacity in congeneric tropical forest shrubs

Abstract

In moist tropical forests resprouting may be an important component of life history, contributing to asexual reproduction through the clonal spread of individuals derived from shoot fragments. However, in contrast to other ecosystems where resprouting is common, the ecological correlates of resprouting capacity in tropical forests remain largely unexplored. In this study we characterized shade tolerance, resprouting capacity and sexual reproductive success of eight co-occurring Piper species from lowland forests of Panama. In field experiments we found that shade-tolerant Piper species had a higher capacity to regenerate from excised or pinned stem fragments than light-demanding species in both gap and understory light conditions. In contrast, shade-tolerant species had lower recruitment probabilities from seeds, as a consequence of lower initial seed viability, and lower seedling emergence rates. All Piper species needed gap conditions for successful seedling establishment. Of 8,000 seeds sown in the understory only 0.2% emerged. In gaps, seed germination of light-demanding species was between 10 and 50%, whereas for shade-tolerant species it was 0.5-9.8%. We propose that the capacity to reproduce asexually from resprouts could be adaptive for shade-tolerant species that are constantly exposed to damage from falling litter in the understory. Resprouting may allow Piper populations to persist and spread despite the high rate of pre-dispersal seed predation and low seed emergence rates. Across Piper species, we detected a trade-off between resprouting capacity and the annual viable seed production per plant but not with annual seed mass produced per plant. This suggests that species differences in sexual reproductive success may not necessarily result from differential resource allocation. Instead we suggest that low sexual reproductive success in the understory may in part reflect reduced genetic diversity in populations undergoing clonal growth, resulting in self-fertilization and in-breeding depression.

Bamboo overabundance alters forest structure and dynamics in the Atlantic Forest hotspot

“…Therefore, it seems that the main process reducing seedling richness act after seed germination, and is probably related to the physical or physiological stress of bamboo-dominated areas. The ability to respond positively to damages varies among species (Clark and Clark, 1991;Simões and Marques, 2007;Lasso et al, 2009) and many can have its performance compromised due to an excess of light/heat or to a lack of soil water availability (Takahashi and Murata, 2008). In addition, it is expected that differences in species richness should be accompanied by differences in composition (Silveira, 2005).…”

Tropical UnderstoryPiperShrubs Maintain High Levels of Genotypic Diversity Despite Frequent Asexual Recruitment

“…This difference may result from variation in resource allocation patterns or from variation in the frequency of stem breakage resulting from greater debris fall in the forest understory (Aide 1987, Clark & Clark 1991. For Piper, field experiments carried out on 22 species in Costa Rica (Greig 1993a), and eight species in Panama (Lasso et al 2009), indicate that shade-tolerant species have a higher capacity to resprout and regenerate by layering and fragmentation relative to congeneric light-demanding species. These studies have also shown that shade-tolerant species tend to have lower sexual reproductive success, suggesting that asexual regeneration may be critical for population persistence.…”

“…Experimental studies of Piper species consistently indicate greater resprouting capacity for shade-tolerant than lightdemanding species (Greig 1993a, Lasso et al 2009). This difference may result from variation in resource allocation patterns or from variation in the frequency of stem breakage resulting from greater debris fall in the forest understory (Aide 1987, Clark & Clark 1991.…”

“…Piper have tiny photoblastic seeds (<< 1 mg; Vázquez-Yanes 1974, Vázquez-Yanes & Smith 1982, Orozco-Segovia & Vázquez-Yanes 1989, Daws et al 2002 that fail to emerge when sown in the understory, even when surface litter is removed. Only 0.2 percent of 8000 seeds sown in the understory emerged for five Piper species studied in Panama (Lasso et al 2009). Likewise, Fleming (1981) found only four surviving seedlings of 1600 seeds of Piper amalago, and Greig (1993a) observed only five surviving seedlings from 3000 seeds of five Piper species, experimentally sown into both gap and understory conditions.…”

“…The original shoot may eventually rot away leaving independent ramets. In fragmentation, new plants resprout from portions of stem or leaf tissue that remains alive on moist soil or leaf litter layers (Greig 1993b;Lasso et al 2009). In both cases, physiologically independent ramets are produced that are difficult to identify as clones unless molecular markers are used.…”