Regeneration filters in post-agricultural fields of Puerto Rico and Ecuador

To better understand how rainforest regenerates after agriculture I sampled the seed rain and seed bank, and set out seeds and seedlings, on microsites defined by distance to the forest in fields both in Puerto Rico and Ecuador. I found that (1) total seeds, species richness and life-form richness were twice as great in the Ecuador seed rain compared to Puerto Rico but Puerto Rico seeds were more evenly distributed among species and (2) total seedlings from the seed bank were similar between Puerto Rico and Ecuador, (3) the majority of seeds were lost to predation among all species and study sites, (4) seed disease was absent in P. aduncum and Miconia prasina, and no seeds germinated for Gonzalagunia spicata and P. riparia, (5) in Ecuador pathogenic disease claimed more seeds than germinated for all species, and Solanum ovalifolium was the only species that had seeds germinate but did not lose seeds to disease, (6) also in Ecuador, insect predation was significantly lower in the forest border for P. aduncum, and seed disease was significantly greater at the 10 m micro site for S. ovalifolium, (7) distance has a significant effect on seedling height and basal diameter, (8) losses of leaf area due to herbivory and pathogens were always low and (9) biomass and leaf specific mass were significantly reduced in the border and forest microsites. I conclude that Ecuador fields had more seeds, species, and life-forms than Puerto Rico fields, predation was the most severe post-dispersal seed filter in all fields, seeds that survived predation on Puerto Rico were lost either to disease or germination but to both mechanisms in Ecuador, all three seed mechanisms in Ecuador fields showed distance effects of seedling growth but not survivorship.     

Seed predation,disease and germination on landslides in Neotropical lower montane wet forest

Abstract. Seed mortality (caused by predators and pathogens) and germination were compared between Puerto Rico and Costa Rica on landslides in lower montane wet forest. Seeds of six common species on five Puerto Rican landslides and four common species on two Costa Rican landslides were used with a Cecropia species and a Gonzalagunia species included at both sites. In the Puerto Rican experiments Cecropia schreberiana was the only species to show significant seed predation (which was due to insects), pathogens grew from all species and fewer seeds were lost to predators than pathogens. Also in Puerto Rico mean germination across all species was 57 % before dispersal (filled seeds collected while still on the tree) and 71 % after, with Phytolacca rivinoides seeds germinating most abundantly, followed in descending order by Ocotea leucoxylon, Cecropia spec, Miconia racemosa, Palicourea riparia and Gonzalagunia spicata. In the Costa Rican experiments three species had significant predation: Cecropia polyphlebia and Urera caracasana (both due to insects) and Witheringia coccoloboides (due to mammals); pathogenic disease caused more seed loss than predation, and germination was high (61 % pre-dispersal, 69 % post-dispersal). Similarities between these island and mainland sites included (1) percentage of seeds lost to predation and percentage lost to pathogens (all in the 5–15 % range), (2) generalist pathogens which claimed more seeds than predators and (3) majority germination with a general increase after dispersal. Finally sites were dissimilar only in the number of species with significant predation loss and whether it was by insects or mammals, casting doubt on the traditional island/mainland dichotomy.     

Barriers to Forest Regeneration in an Abandoned Pasture in Puerto Rico

Sources of forest regeneration (soil seed bank, seed rain) and barriers to seedling establishment were examined in a recently abandoned pasture in eastern Puerto Rico. Few woody species were found in the soil seed bank or in the seed rain. The number of seeds and species in the seed rain and soil seed bank declined with distance from the adjacent secondary forest. Nine species naturally dispersed and colonized plots during the study, with the wind‐dispersed tree Tabebuia heterophylla being the predominant colonizer (91% of all seedlings). Barriers to seedling establishment were determined using a blocked field experiment with eleven woody species representative of a variety of life histories. Each species was planted under the pasture vegetation (control) or in areas where all vegetation was removed (removal). Germination was enhanced for four species in the control treatment, five species were not affected, and two species did not germinate under either treatment. Survival to 6 months was higher in the removal treatment for two species. Seedling biomass was greater in the removal treatment at 12 months for one species. Seed mass was a good predictor of germination success and final shoot biomass, but not survival. This study demonstrates that seeding recently abandoned pastures with a mix of known pioneer species may accelerate the rate of secondary succession, but some species will have to be planted in later successional stages in order to overcome strong barriers to establishment.     

An experimental test of density- and distant-dependent recruitment of mahogany (Swietenia macrophylla) in southeastern Amazonia

According to the Janzen–Connell model, high mortality of seeds and seedlings in proximity to conspecific adults can help maintain species diversity in tropical forests. Using a natural population of big-leaf mahogany (Swietenia macrophylla King), we tested the model’s mechanism by examining seed predation and juvenile recruitment in the forest understory and in treefall gaps in the vicinity of both isolated and clumped adults. We used tethered seeds placed in three types of exclosure plots: (1) complete access to seeds, (2) semi-access (access by small-sized seed predators) and (3) no access (all mammals excluded). Exclosure treatments were applied within the understory (both near and far from adults) and in gaps at eight fruiting adults in the late dry season (2001) and scored ten months later. Significantly more seeds were removed in canopy gaps near clumped adults than at isolated adults; otherwise, none of the treatment factors significantly influenced seed predation. In contrast, understory juvenile recruitment was significantly enhanced by distance from adults and was twice as high at isolated than clumped adults, providing novel support for the Janzen–Connell mechanism. No-access exclosures protected significantly more seeds than semi- and full-access exclosures, implicating small mammals in seed losses. Across the eight trees, juvenile recruitment in the no-access exclosures decreased significantly with conspecific adult densities, implicating non-mammalian density-responsive factor(s) in mortality following germination; likely a known specialist invertebrate herbivore. When all treatments were combined, conspecific adult basal area and total DBH explained 72 and 90% of variation in overall juvenile recruitment, respectively. Collectively, these results indicate that Janzen–Connell effects can operate in S. macrophylla, especially during the seed-to-seedling transition, and will likely reduce recruitment in areas of high conspecific densities. They also suggest that further research into the causes of density-dependence in tropical trees should investigate mortality agents following germination.     

Seed Availability as a Limiting Factor in Forest Recovery Processes in Costa Rica

Abandoned pastures and secondary forests are increasingly prominent features of tropical landscapes. Forest regrowth on abandoned pastures is generally slow and virtually limited to regeneration from seeds from external sources, since agricultural activities alter site conditions. We hypothesize that seed availability is a major limiting factor in forest recovery on abandoned pastures. This hypothesis was tested by studying the seed bank, seed rain, and seed predation in a small pasture (1 ha) situated in a forest‐pasture mosaic in northwestern Costa Rica. The tree seed density in the pasture seed bank was much lower (21/m²) than the density in the seed bank of a neighboring secondary forest (402/m²). Within a period of five weeks, 23 tree seeds entered the pasture by seed rain. This number is low compared to densities found in closed forests but higher than densities reported in other studies where virtually no seeds were found beyond 20 m from the forest edge. Possibly the small size of the pasture with seed sources nearby and the small‐scale landscape mosaic enhance seed dispersal. Predation limits the seed density in pastures, with 42% of the woody species consumed by predators. The low seed density in the seed bank, and hampered recruitment combined with significant losses, pose severe restrictions to forest recovery on abandoned pastures. Moderate land use, and small sized clearings with seed sources nearby may increase the pace of recovery. Nevertheless, forest establishment may still take a considerable time. Thus, enlarging the available pool of species may be a worthwhile management strategy.     

Green Iguanas (Iguana iguana) in Puerto Rico: is it time for management?

Iguana iguana is native to Central and South America, and was introduced into Puerto Rico in the 1970s as a result of pet trade. The invasive biology of this reptile has not been studied in Puerto Rico, where its negative effects may threaten local biodiversity. The purposes of this study were to: (1) estimate population densities of I. iguana; (2) describe some aspects of its reproductive biology; and (3) assess its potential impacts. Visual-encounter surveys were performed at Parque Lineal in San Juan and Canal Blasina in Carolina, while nesting activity data were collected at Las Cabezas de San Juan in Fajardo. Densities of I. iguana in Puerto Rico reached a maximum of 223 individuals ha⁻¹, higher than in any known locality in its native range, and showed fluctuations related to seasonality. Our 2008–2009 observations at the nesting sites document that this population of I. iguana is a reproductively successful species, producing more than 100 egg clutches and 2,558 eggs with a 91.4% egg viability. The ability to proliferate in a low predation environment and the absence of good competitors are the major drivers of the population densities observed in Puerto Rico. We found evidence that I. iguana is threatening native biodiversity and impacting infrastructure, agriculture and human safety. Thus, a management program to control the species must soon be developed to prevent this invasive reptile from becoming more widespread and dominant in other localities around the island.     

Postdispersal seed predation and seed viability in forest soils: implications for the regeneration of tree species in Ethiopian church forests

Almost all dry Afromontane forests of Northern Ethiopia have been converted to agricultural, grazing or scrub lands except for small fragments left around churches (‘Church forests’). Species regeneration in these forests is limited. We investigated (i) how intense postdispersal seed predation was in church forest, and if this seed predation varied with species and/or habitat, and (ii) for how long tree seeds maintained their viability while buried in forest soil. In the seed predation experiment, we monitored seeds of six tree species in four habitats for a period of 14 weeks (the peak seeding season). In the seed viability experiment, we assessed seed viability of five species in four habitats after being buried 6, 12, or 18 months. Ninety‐two percent of the tree seeds were predated within 3.5 months. Predation was mainly dependent on species whereas habitat had a weaker effect. Seed viability decreased sharply with burial time in soil for all species except for Juniperus. To minimize seed availability limitation for regeneration of such species in the forest, the standing vegetation needs to be persistently managed and conserved for a continuous seed rain supply. Additional seed sowing, and seed and seedling protection (by e.g. animal exclosures) may increase successful regeneration of important species in these forests.     

Interaction between ungulates and bruchid beetles and its effect on <Emphasis Type="Italic">Acacia</Emphasis> trees: modeling the costs and benefits of seed dispersal to plant demography

Integrative studies of plant–animal interactions that incorporate the multiple effects of interactions are important for discerning the importance of each factor within the population dynamics of a plant species. The low regeneration capacity of many Acacia species in arid savannas is a consequence of a combination of reduction in seed dispersal and high seed predation. Here we studied how ungulates (acting as both seed dispersers and herbivores) and bruchid beetles (post-dispersal seed predators) modulate the population dynamics of A. raddiana, a keystone species in the Middle East. We developed two simulation models of plant demography: the first included seed ingestion by ungulates and seed predation by bruchids, whereas the second model additionally incorporated herbivory by ungulates. We also included the interacting effects of seed removal and body mass, because larger ungulates destroy proportionally fewer seeds and enhance seed germination. Simulations showed that the negative effect of seed predation on acacia population size was compensated for by the positive effect of seed ingestion at 50 and 30% seed removal under scenarios with and without herbivory, respectively. Smaller ungulates (e.g., <35 kg) must necessarily remove tenfold more seeds than larger ungulates (e.g., >250 kg) to compensate for the negative effect of seed predation. Seedling proportion increased with seed removal in the model with herbivory. Managing and restoring acacia seed dispersers is key to conserving acacia populations, because low-to-medium seed removal could quickly restore their regeneration capacity.     

Consequences of habitat disturbance on seed fate of a Brazilian tropical dry forest tree Cavanillesia arborea (Malvaceae)

We compared seed fate (survival, mortality by rodent predators, desiccation and other causes) of the tree Cavanillesia arborea (Malvaceae) in preserved old‐growth tropical dry forests and in nearby abandoned pasturelands in Brazil. For this purpose, we performed an experiment where 15 seeds were placed in the surroundings of 15 parental individuals in each habitat. These 450 seeds were monitored over four months. At the end of the experiment, seed predation by rodents was higher in forest (56.5%) than in pasture (8.9%) areas, but seed desiccation showed the opposite pattern (8.9% vs. 80.4%). Mortality by desiccation was also faster in pasture than in forest areas, probably reducing their attractiveness to predators in these areas. None of the seeds placed in the pasture survived, whereas 26.2% of seeds became seedlings in forest areas. The absence of seedling recruitment of Cavanillesia arborea in pastures is likely a consequence of their incapacity to tolerate the harsh abiotic conditions in this habitat. Thus, forest conversion imposes a strong limitation to the long‐term population viability of this species. However, restoration and natural regeneration of abandoned pastures can recreate the forest structure and microclimatic conditions favourable to seed germination and seedling establishment. Remnant individuals of Cavanillesia arborea in agricultural landscapes may have a negligible contribution to current recruitment, but they can attract potential dispersers of pioneer species, with positive feedbacks to future recruitment during secondary succession.     

Effects of invasive Green Iguanas (<Emphasis Type="Italic">Iguana iguana</Emphasis>) on seed germination and seed dispersal potential in southeastern Puerto Rico

Green Iguanas (Iguana iguana) are invasive in Puerto Rico due to a variety of negative economic effects, yet we know very little about their ecological impacts. Because they are herbivorous, defecate intact seeds, move through the forest, and have long gut-passage times, Green Iguanas may affect seed germination and seed dispersal. In summer 2013, a total of 258 Green Iguana scat samples were collected at the Humacao Natural Reserve in southeastern Puerto Rico. Seeds extracted from scat and collected from fruit were planted under common garden conditions using experimental treatments designed to tease apart the effects of feces, fruit, and ingestion on seed germination. Green Iguanas decreased the time for seeds to germinate in Ficus spp. by removing fruit pulp, but had no effect on germination of native Annona glabra seeds. For non-native P. pterocarpus and Pterocarpus spp., Green Iguanas produced conflicting results, decreasing the percentage of seeds germinating, but at the same time, reducing the time for seeds to germinate. Green Iguanas likely disperse most seeds beyond the canopies of parental tree at our site. Government and economic resources are being used to eradicate Green Iguana populations in Puerto Rico, but the lack of consistent effects of Green Iguanas on seed germination for the plant species consumed at our site complicates generalizing about their ecological effects and developing management plans that minimize negative effects for native plant communities. We recommend additional studies that target both species of particular concern, such as threatened native or invasive species, as well as studies of sensitive habitats in Puerto Rico.     

Primary Seed Dispersal by Red Howler Monkeys and the Effect of Defecation Patterns on the Fate of Dispersed Seeds1

The effectiveness of a seed disperser depends on the quantity and quality of dispersal. The quality of dispersal depends in large part on factors that affect the post–dispersal fate of seeds, and yet this aspect of dispersal quality is rarely assessed. In the particular case of seed dispersal through endozoochory, the defecation pattern produced has the potential of affecting the fate of dispersed seeds and consequently, dispersal quality and effectiveness. In this study, I assessed the effects of dung presence and dung/seed densities on seed predation by rodents and secondary dispersal by dung beetles. In particular, I compared seed fates in clumped defecation patterns, as those produced by howler monkeys, with seed fates in scattered defecation patterns, as those produced by other frugivores. I also determined the prevalence of red howler monkeys (Alouatta seniculus) as seed dispersers at the plant community level in Central Amazonia by determining the number of species they dispersed in a 25–month period. I found that dung presence and amount affected rodent and dung beetle behavior. Seed predation rates were higher when dung was present, and when it was in higher densities. The same number of seeds was buried by dung beedes, in dumped versus scattered defecation patterns, but more seeds were buried when they were inside large dung–piles versus small piles. Seed density had no effect on rodent or dung beetle behavior. Results indicate that caution should be taken when categorizing an animal as a high or low quality seed disperser before carefully examining the factors that affect the fate of dispersed seeds. Red howler monkeys dispersed the seeds of 137 species during the study period, which is the highest yet reported number for an Alouatta species, and should thus be considered highly prevalent seed dispersers at the plant community level in Central Amazonian terra firme rain forests.     

Comparative Seed Dispersal Effectiveness of Sympatric Alouatta guariba and Brachyteles arachnoides in Southeastern Brazil1

I compared the effectiveness of sympatric brown howlers (Alouatta guariba) and muriquis (Brachyteles arachnoides) as seed dispersers in terms of quantitative and qualitative attributes. I hypothesized that differences in feeding and behavioral patterns between these large‐bodied folivorous/frugivorous primates would lead to dissimilarities in their effectiveness as endozoochoric seed dispersal agents. The study was carried out in a semideciduous forest fragment of Fazenda Barreiro Rico, southeastern Brazil. Through behavioral sampling of frugivory and defecation events as well as analyses of fecal samples, I determined that A. guariba dispersed fewer species and produced a lower proportion of dung with intact seeds than B. arachnoides. There was no difference between the number of seeds in fecal samples of A. guariba and B. arachnoides. These primates affected to a similar degree both germination percentage and latency to germination of seeds they ingested or removed the pulp from. Howlers and muriquis were also similar in carrying seeds away from the parent trees. Contrary to muriquis, howlers defecated seeds under the canopy of conspecific lianas, where seeds are expected to suffer high mortality rates, and voided seeds predominantly in a clumped pattern. B. arachnoides was a more effective seed disperser when compared to A. guariba in some attributes evaluated, but not in others. Given the interspecific variation in recruitment patterns of tropical plants and the loss of frugivorous bird species at the study site, the differences between howlers and muriquis in their abilities as seed dispersers may crucially influence the composition and maintenance of seedling diversity.     

Invasion by native tree species prevents biotic homogenization in novel forests of Puerto Rico

There is concern that secondary forests dominated by introduced species, known as novel forests, increase taxonomical similarity between localities and lead to biotic homogenization in human-dominated landscapes. In Puerto Rico, agricultural abandonment has given way to novel forests dominated by the introduced African tulip tree Spathodea campanulata Beauv. (Bignoniaceae). In this study, I characterized the tree species composition of S. campanulata forests in Puerto Rico as means to evaluate if biotic homogenization is occurring. Non-metric multidimensional scaling was used to examine what variables were related to the large (≥10 cm diameter at breast height [DBH]), small (≥2.5 to <10 cm DBH), and juvenile (<2.5 cm DBH) tree species composition of 20 sites. Species composition was strongly related to substrate properties, less related to land use history, and unrelated to spatial attributes. The introduced species component was low (mean = 17%, S.E. = 1.8) and compositional differences were mostly due to native tree species of secondary to old growth forests on equivalent substrates. Animals appear to disperse most species (86%) into these forests yet because of this some introduced species will persist. Although uncommon species were largely absent, recent species establishment is shaped by substrate properties making biotic homogenization in these forests unlikely. The S. campanulata forests of Puerto Rico facilitate native tree species establishment in lands where poor management practices extirpated the original forest. These results highlight the importance of remnant old growth forests or trees that act as seed dispersal sources and facilitate native species recovery in novel forests.     

Effects of forest clearing and succession on the carbon and nitrogen content of soils in Puerto Rico and US Virgin Islands

Soil samples from mature and secondary forests and agricultural sites in three subtropical life zones of Puerto Rico and the US Virgin Islands were collected to determine the effects of forest conversion to agriculture and succession on soil organic carbon (C) and nitrogen (N) contents. Site characteristics that may affect soil C and N (slope, elevation, aspect, and texture) were as uniform as possible. Carbon contents (to 50 cm depth or bedrock) of cultivated sites, as a percent of corresponding mature forests, were lower in the wet (44%) and moist (31%) than in the dry (86%) life zones whereas N contents were relatively high regardless of life zone (60–130% of the mature forests). Conversion of forests to pasture resulted in less soil C and N loss than conversion to crops. The time for recovery of soil C and N during succession was approximately the same in all three life zones, about 40–50 yr for C about 15–20 yr for N. However, the rate of recovery of soil C was faster in the wet and moist life zone, whereas N appeared to recover faster in the dry life zone. Evidence for loss of soil C during cultivation and gain during succession to soil depths of 50–100 cm is presented.     

High regeneration capacity helps tropical seeds to counter rodent predation

Rapid germination of non-dormant seeds is one adaptation plants have evolved to counter seed predation by rodents. Some rodent species have evolved behaviors that prevent or slow the seed germination process through seed embryo removal or seed pruning; however, no plant species is known to have successfully escaped embryo removal or seed pruning by rodents. Here, we report that the non-dormant seeds of Pittosporopsis kerrii Craib in tropical rain forests in China have a high regeneration capacity to counter seed pruning by rodents. We found seed pruning, instead of embryo removal, was commonly used by rodents to increase food storage time by slowing down the seed germination process, but that P. kerrii seeds have a high regeneration capacity to escape seed predation by rodents: all pruned seeds, pruned roots and embryo-removed seeds by rodents or people retain the ability to develop into seedlings. Seeds of P. kerrii also have other capacities (i.e. rapid seed decomposition and indigestible dormant taproots) to escape predation by reducing the plant’s attractiveness to rodents. The association between seed pruning behavior in rodents and high regeneration capacity of pruned seeds or roots in P. kerrii seeds are likely novel adaptation strategies adopted by seeds and rodents, respectively.     

Apparent competition: an impact of exotic shrub invasion on tree regeneration

Invasion of habitats by exotic shrubs is often associated with a decrease in the abundance of native species, particularly trees. This is typically interpreted as evidence for direct resource competition between the invader and native species. However, this may also reflect indirect impacts of the exotic shrubs through harboring high densities of seed predators––known as apparent competition. Here I present data from separate seed predation experiments conducted with two shrub species exotic to North America; Rosa multiflora, an invader of abandoned agricultural land, and Lonicera maackii, an invader of disturbed or secondary forest habitats. Both experiments showed significantly greater risks of seed predation for tree seeds located under shrub canopies when compared to open microhabitats within the same site. These results indicate the potential importance of indirect impacts of exotic species invasions on native biota in addition to the direct impacts that are typically the focus of research.     

Leaf-cutting ant nests support less dense and impoverished seed assemblages in a human-modified Caatinga dry forest

Regenerating forests make up an increasingly large portion of tropical landscapes worldwide and regeneration dynamics may be influenced by leaf-cutting ants (LCA), which proliferate in disturbed areas and collect seeds for fungus culturing. Here, we investigate how LCA influences seed fate in human-modified areas of Caatinga dry forest. We evaluate the seed deposition and predation on Atta opaciceps nests, foraging habitat surrounding nest and control habitat away of nest influence of 15 colonies located along a forest cover gradient during the rainy and dry seasons. For each habitat, four 50-cm² plots were established and all seeds on the soil surface were collected along 1 year. We recorded 13,628 seeds distributed among 47 species and 36.57% of the total seeds did not show any sign of predation. Nest mound habitats supported low-density and species-poor seed assemblages, which were taxonomically distinct from the control habitats. These effects only occurred in the rainy season. The proportion of undamaged seeds were similar across the habitats. While forest cover did not influence seed assemblage in terms of species richness or seed predation, it did interact with habitat type via increments in seed abundance as forest cover increased across the nests. Forest cover also affected seed composition, but only in the rainy season. These results indicate that LCA decrease seed deposition in areas under their influence, particularly on the nest mounds. As LCA profit from human disturbance in the Caatinga, their role as seed ‘sinks’ should be enhanced in disturbed Caatinga patches, particularly during the rainy season, when most of the plant recruitment occurs. Our findings reinforce the importance of LCA as drivers of forest dynamics and resilience in human-modified landscapes.     

Mechanisms of plant regeneration during succession after shifting cultivation in eastern Amazonia

The role of seed bank, seed rain, and regeneration from seedlings and sprouts after swidden agriculture was compared in 5-, 10- and 20-year-old secondary forest and in a primary forest in Bragantina, Pará, Brazil. The seed bank (0–5 cm soil depth) was largest in the 5-year-old forest (1190 ± 284 seeds m⁻²) and decreased nearly ten-fold with age to 137 ± 19 seeds m⁻² in the primary forest. The highest seed rain was in the 5-year-old forest (883 ± 230 seeds m⁻² year⁻¹) and the least in the primary forest (220 ± 80 seeds m⁻² year⁻¹). Large plants (≥5 cm dbh) had more individuals and species that regenerated from sprouts than from seeds and the most abundant tree species in the secondary forest stands of all ages appear to be maintained by sprouting. The smaller individuals (≥1 m tall, <5 cm dbh) in the 5-year-old forest were mainly from sprouts, but those in the older secondary forests originated mainly from seeds. These results show that at the beginning of succession, although many species can be introduced to swidden fallow from seed bank and seed rain, it is the sprout that is the main source of recruits of primary forest species in secondary forests in Bragantina.     

Postdispersal Seed Fate of Tropical Montane Trees in an Agricultural Landscape, Southern Costa Rica

Variation in postdispersal seed fate is an important factor driving patterns of forest regeneration. Because most previous studies have not tracked final seed fate and have commonly equated seed removal with predation without considering the possibility of secondary dispersal, little is known about individual seed mortality factors in successional and degraded habitats. This study tracked the postdispersal fate of large-seeded tropical montane trees in abandoned pasture, young secondary forests, and small forest fragments during two consecutive years in an agricultural landscape in southern Costa Rica. The incidence of secondary dispersal by animals, scatterhoarding in particular, and the effects of seed burial on germination were measured. Overall, seeds survived through germination more often in secondary forests with high levels of mortality occurring in abandoned pastures and forest fragments. The majority of seed mortality was caused by rodent predation in forest fragments, insects and fungal pathogens in secondary forests, and a combination of desiccation, insects, and fungal pathogens in pastures. Seeds were frequently secondarily dispersed in larger forest fragments, whereas they were only rarely moved in pastures and secondary forests. Burial tended to improve germination in pastures and was important for an often scatterhoarded species, Otoba novogranatensis, in all habitats. The results of this study suggest that: (1) seed mortality factors differ in response to the type of habitat degradation; (2) large-seeded species have high potential for survival when dispersed to young secondary forests; and (3) seed removal is not a reliable proxy for seed predation, particularly in less degraded forest fragments.     

Habitat use and seed removal by invasive rats (Rattus rattus) in disturbed and undisturbed rain forest,Puerto Rico

Despite frequent occurrences of invasive rats (Rattus spp.) on islands, their known effects on forests are limited. Where invasive rats have been studied, they generally have significant negative impacts on native plants, birds, and other animals. This study aimed to determine invasive rat distribution and effects on native plant populations via short‐term seed removal trials in tropical rain forest habitats in the Luquillo Experimental Forest, Puerto Rico. To address the first objective, we used tracking tunnels (inked and baited cards inside tunnels enabling animal visitors’ footprints to be identified) placed on the ground and in the lower canopy within disturbed (treefall gaps, hurricane plots, stream edges) and undisturbed (continuous forest) habitats. We found that rats are present in all habitats tested. Secondly, we compared seed removal of four native tree species (Guarea guidonia, Buchenavia capitata, Tetragastris balsamifera, and Prestoea acuminata) between vertebrate‐excluded and free‐access treatments in the same disturbed and undisturbed habitats. Trail cameras were used to identify animals responsible for seed contact and removal. Black rats (Rattus rattus) were responsible for 65.1% of the interactions with seeds, of which 28.6% were confirmed seed removals. Two plant species had significantly more seeds removed in disturbed (gaps) than undisturbed forest. Prestoea acuminata had the lowest seed removal (9% in 10 days), whereas all other species had >30% removal. Black rats are likely influencing fates of seeds on the forest floor, and possibly forest community composition, through dispersal or predation. Further understanding of rat–plant interactions may be useful for formulating conservation strategies.