Reproductive potential and seedling establishment of the invasive alien tree Schinus molle (Anacardiaceae) in South Africa

Schinus molle (Peruvian pepper tree) was introduced to South Africa more than 150 years ago and was widely planted, mainly along roads. Only in the last two decades has the species become naturalized and invasive in some parts of its new range, notably in semi‐arid savannas. Research is being undertaken to predict its potential for further invasion in South Africa. We studied production, dispersal and predation of seeds, seed banks, and seedling establishment in relation to land uses at three sites, namely ungrazed savanna once used as a military training ground; a savanna grazed by native game; and an ungrazed mine dump. We found that seed production and seed rain density of S. molle varied greatly between study sites, but was high at all sites (384 864–1 233 690 seeds per tree per year; 3877–9477 seeds per square metre per year). We found seeds dispersed to distances of up to 320 m from female trees, and most seeds were deposited within 50 m of putative source trees. Annual seed rain density below canopies of Acacia tortillis, the dominant native tree at all sites, was significantly lower in grazed savanna. The quality of seed rain was much reduced by endophagous predators. Seed survival in the soil was low, with no survival recorded beyond 1 year. Propagule pressure to drive the rate of recruitment: densities of seedlings and sapling densities were higher in ungrazed savanna and the ungrazed mine dump than in grazed savanna, as reflected by large numbers of young individuals, but adult : seedling ratios did not differ between savanna sites. Frequent and abundant seed production, together with effective dispersal of viable S. molle seed by birds to suitable establishment sites below trees of other species to overcome predation effects, facilitates invasion. Disturbance enhances invasion, probably by reducing competition from native plants.     

Disperser- vs. Establishment-Limited Distribution of a Riparian Fig Tree (Ficus insipida) in a Costa Rican Tropical Rain Forest1

Studies were conducted at the La Selva Biological Station in Costa Rica and in a greenhouse in California to determine the factors accounting for the nonrandom distribution of the riparian fig tree Ficus insipida Willd. along streams in the La Selva Biological Reserve and adjacent deforested lands. We also evaluated the potential seed dispersers of this tree relative to the role of the fruit‐eating fish Brycon guatemalensis that previously was proposed to be an important disperser of F. insipida seeds in this system. At La Selva, we recorded the fig‐foraging activities of vertebrates at fruiting F. insipida trees, surveyed for the presence or absence of F. insipida along streams of different sizes, and determined the fate of fig seedlings transplanted in different riparian habitats. In the greenhouse, we measured seed germination and seedling survival and growth under different light and soil pH conditions mimicking natural conditions. The findings provided evidence that (1) the tree occurs along the larger streams running through forest habitat and only along smaller streams with relatively high light availability; (2) bats (Artibeus spp.) and fish are the major dispersers of F. insipida seeds; (3) the seedlings are subject to mortality not only from low light conditions but also from treefalls, frequent flooding, and bank erosion; and (4) high light levels and near neutral soil pH result in relatively better seed germination, faster growth, and higher survival rates of seedlings. Overall, our results suggest that this fig tree is dispersed mainly by bats and fish and is more establishment‐limited than disperser‐limited in its local distribution in the La Selva rain forest habitat.     

Frugivory and Seed Fate in Bursera inversa (Burseraceae) at Tinigua Park,Colombia: Implications for Primate Conservation1

The large ateline primates are efficient seed dispersers in Neotropical forests and hunting is driving their populations to extinction, but we do not know whether other frugivores could substitute primates in their ecological role as seed dispersers. In this study we test this possibility using a potential keystone species (Bursera inversa) at Tinigua Park, Colombia. This plant species allows us to compare seed removal rates between emergent, isolated trees, without primate visitors and trees with connected crowns. We used traps to estimate fruit production and seed removal rates in six different trees, and fruiting trees were observed during 2 yr to quantify the number of seeds manipulated by different animal species. We carried out seed predation experiments to test if seed removal by predators was affected by distance or density effects. We found that the most productive trees attracted more visiting species and seed removal rates differed among trees, the lowest corresponding to trees without primate access. Seed removal rates from the ground by predators were not higher below parental trees than away from them, but the distribution of saplings in the forest suggests that seed dispersal is advantageous. Although it is likely that the effect of primate extinctions will vary depending on tree species traits, conserving the populations of primate seed dispersers is critical to maintain the ecological processes in this forest.     

Effects of Dispersal Pattern and Mammalian Herbivores on Seedling Recruitment for Virola michelii (Myristicaceae) in French Guiana1

The effects of dispersal pattern (seeds in small clumps vs. seeds scattered in pairs) and distance to the nearest Carapa procera (Meliaceae; a tree that produces seeds preferred by terrestrial vertebrates) on survival of seeds and seedlings were examined for the animal–dispersed tree species Virola michelii (Myristicaceae) in a mature forest‘at Paracou, French Guiana, in 1992 and 1993. We assessed the putative role of ground–dwelling mammalian herbivores, rodents, and ungulates that filter the seed shadow, acting either as dispersers or predators and thus modifying the original pattern of seed dispersal made by frugivores. We measured the effects of simulated seed burial by rodents using marked seeds and quantified the effect of protecting seeds and seedlings from ground–dwelling vertebrates on seedling germination and survival with fence exclosures in 1992. Dispersal pattern had short–term but no long–term effects on the proportion of V. michelii seeds that survived one year later as seedlings. In the short term, within six weeks, clumped seeds survived better than scattered seeds in both years. Marked seeds that were removed from their site of dispersal were eaten; rodents only rarely buried seeds of V. michelii, and seed burial reduced seed and seedling survivorship. The combined effect of the factors year and Carapa proximity significantly affected seed survival within six weeks. Although six–week seed survival was greater in 1993 than in 1992, seedling establishment was lower in 1993 than in 1992 following a lower rainfall regime during the key period of seed germination (February). One–year seed and seedling survivorship was similar between treatments and years. Seed survival and seedling establishment in V. michelii was dependent on vertebrates in the short term and on climate in the long term. Overall, seed and seedling survivorship depended on a combination of these factors.     

Effects of Tree Guards and Weed Mats on the Establishment of Native Tree Seedlings: Implications for Forest Restoration in Hong Kong, China

The effects of tree guards and weed mats on establishment and growth of native tree seedlings, Thick‐leaved oak (Cyclobalanopsis edithiae (Skan) Schott., Fagaceae), planted in an exposed hillside grassland in Hong Kong, were investigated. The natural regeneration of C. edithiae is poor due to a lack of seed dispersal agents and high seed predation, and therefore, this species is often targeted for forest restoration. The experiment lasted for 3.5 years during which the height, basal diameter, and crown diameter of individual seedlings were measured and survivorship recorded. The use of weed mats alone did not have a significant effect, but a combination of tree guards and weed mats led to a significant improvement in establishment, survivorship, and growth of the seedlings during the experimental period. Initially, the guards promoted rapid height growth of the seedlings, although lateral growth and secondary stem thickening were compromised. After the seedlings grew over the tree guards, the basal diameter and crown diameter increased at a notably faster rate. The combined effect of the tree guard and weed mat on the seedling growth pattern was found to be beneficial and contributed to the high survivorship of the seedlings. Comparing the survivorship data and the costs of various treatments, the use of tree guards in combination with the weed mats was demonstrated to be more cost‐effective than planting the seedlings without tree guards or weed mats. The potential for applying the technique in afforestation programs with native tree species for forest restoration in Hong Kong and other tropical regions is discussed.     

Seed dispersal, plant recruitment and spatial distribution of Bactris acanthocarpa Martius (Arecaceae) in a remnant of Atlantic forest in northeast Brazil

Seed dispersal ecology of Bactris acanthocarpa Mart. (Arecaceae), an Atlantic forest understory palm, was investigated during two years as an attempt to test the following predictions: (i) seeds of Bactris are dispersed by mammals and large-gaped birds; (ii) Bactris benefits from seed dispersal in terms of seed predation avoidance, improvement of seed germination and seedling survival; and (iii) spatial distribution of adults is related to patterns of seed dispersal. The study was conducted at Dois Irmãos Reserve, a 387.4-ha reserve of Atlantic forest in northeastern Brazil (8º S–35º W). Black–rumped agoutis (Dasyprocta prymnolopha) and Guianan squirrels (Sciurus aestuans) were identified as the seed dispersers/predators, moving seeds short distances (< 4 m from parents) and at low rates (0.04-0.05 diaspore/palm/day). Pyrene burial prevented seed predation by vertebrates and reduced by half seed infestation by Scolytidae beetles. Only buried pyrenes germinated. Pyrene predation was not correlated with distance from conspecific adults. In contrast, early seedling mortality was higher near conspecific adults. Most adults (64%) had their nearest conspecific adult neighbour > 4 m away in contrast to 96% of seedlings that occurred concentrated within 4 m from adults (77% under the palm crowns). Here, we present evidence that spatial distribution of B. acanthocarpa is partly due to low rates of seed removal, short-distance seed dispersal by agoutis and squirrels, and early seedling mortality associated with presence of seedlings under palm crowns.     

Seeds and seedlings of oaks suffer from mammals and molluscs close to phylogenetically isolated,old adults

Background and AimsMammals and molluscs (MaM) are abundant herbivores of tree seeds and seedlings, but how the trees and their environment affect MaM herbivory has been little studied. MaM tend to move much larger distances during the feeding stage than the more frequently studied insect herbivores. We hypothesize that MaM (1) select and stay within the patches that promise to be relatively the richest in seeds and seedlings, i.e. patches around adult trees that are old and within a distantly related, less productive neighborhood; and (2) try to remain sheltered from predators while foraging, i.e. mammals remain close to adult trees or to cover by herbs while foraging, and might force their mollusc prey to show the opposite distribution.MethodsWe exposed oak acorns and seedlings in a temperate forest along transects from adult conspecifics in different neighbourhoods. We followed acorn removal and leaf herbivory. We used exclusion experiments to separate acorn removal by ungulates vs. rodents and leaf herbivory by insects vs. molluscs. We measured the size of the closest conspecific adult tree, its phylogenetic isolation from the neighbourhood and the herbaceous ground cover.Key ResultsConsistent with our hypothesis, rodents removed seeds around adult trees surrounded by phylogenetically distant trees and by a dense herb cover. Molluscs grazed seedlings surrounding large conspecific adults and where herb cover is scarce. Contrary to our hypothesis, the impact of MaM did not change from 1 to 5 m distance from adult trees.ConclusionsWe suggest that foraging decisions of MaM repulse seedlings from old adults, and mediate the negative effects of herbaceous vegetation on tree recruitment. Also, an increase in mammalian seed predation might prevent trees from establishing in the niches of phylogenetically distantly related species, contrary to what is known from insect enemies.     

Seed-spitting Primates and the Conservation and Dispersion of Large-seeded Trees

Primate frugivory may reduce density-dependent predation on seeds and seedlings via effective seed dispersal. Accordingly, the tendency of cercopithecines to spit and scatter seeds > 4 mm wide could represent a prominent means of dispersal. However, the importance of seed-spitting may vary according to the life history adaptations of plants. Indeed, the actions of cercopithecines may be incongruent with the reproductive biology of plants that rely on large frugivores to swallow and defecate their seeds. This possibility raises conservation concerns because large frugivores are often susceptible to extirpation or extinction from hunting and habitat fragmentation. It is therefore important to determine if cercopithecines have a compensatory effect; that is, whether or not seed-spitting effectively conveys large seeds to recruitment sites. To test this concept, we used geospatial techniques to measure and analyze the dispersion of tree species dispersed by elephants, chimpanzees, and cercopithecines to different spatial extents. We studied adult trees of Balanites wilsoniana, Chrysophyllum gorungosanum, and Uvariopsis congensis in a 2.2-ha plot in Kibale National Park, Uganda. Despite the tendency of cercopithecines to spit the seeds of Uvariopsis congensis, adult trees were highly clumped, with a modal nearest-neighbor distance of < 5 m and a crown overlap of 1.5 m. Virtually identical results for Balanites wilsoniana and Chrysophyllum gorungosanum, the seeds of which are not spat, suggest that seed-spitting may be a poor mechanism of dispersal for some large-seeded plants.     

北京东灵山落叶阔叶林中辽东栎种子雨

在北京东灵山地区的一个落叶阔叶林中调查了辽东栎（Ｑｕｅｒｃｕｓ ｌｉａｏｔｕｎｇｅｎｓｉｓ Ｋｏｉｄｚ．）的种子雨。对于选定的４棵辽东栎中的３棵,树冠下的种子雨分布格局符合二次分布,具有很高的决定系数。由设置在树冠下的种子捕捉器收集的坚果数量来估计整棵树的种子雨。４棵树的种子雨中有活力的种子很少,变化范围从２６到２５９个。每棵树的树冠下的种子雨密度变化范围从０．７６到７．２６个／ｍ＾２。林中平均种     

Seed protection through dispersal by African savannah elephants (Loxodonta africana africana) in northern Tanzania.

We examined effectiveness of African savannah elephant dung as a protective barrier for seeds of three tree species, Acacia tortilis Hayne, Tamarindus indica L. and Ximenia aegyptiaca L. Seeds were collected from dung and underneath fruiting trees in Tarangire National Park, Tanzania. Experimental treatments were established to test: (i) the efficacy of dung in protecting seeds of A. tortilis from bruchid beetle infestation and the role of animals larger than insects in removing seeds; (ii) the same tenets as in Experiment 1, using seeds of T. indica; and (iii) the effect of distance on survival of seeds of X. aegyptiaca. Sites were established during two field seasons underneath conspecific trees, where seed predation was likely highest. Repeated‐measures two‐way ANOVA indicated that there was no treatment effect for Experiment 1. For Experiments 2 and 3 in October 2013, seeds in dung experienced less beetle infestation than fresh seeds. Repeated‐measures two‐way ANOVA and Tukey's HSD indicated that treatment effect differed among all treatments. Passed seeds at distances ≥5 m experienced less beetle infestation than fresh seeds underneath conspecifics. African savannah elephants appear to be important seed dispersers of these three tree species.     

Assessment of the Biological Control Impact of Seed Predators on the Invasive Shrub Acacia nilotica (Prickly Acacia) in Australia

An impact assessment study was undertaken to determine seed predation rates by two bruchid beetles, Bruchidus sahlbergi Schilsky and Caryedon serratus Olivier, on the invasive shrub Acacia nilotica (L.) Willd. ex Del. The former bruchid was released as a biological control agent for A. nilotica, whereas the latter is naturalized in Australia. We attempted to determine the dynamics and magnitude of bruchid predation, following a number of differing reports of their effectiveness. To investigate the importance of seed availability on bruchid numbers, we compared seed death in high- and low-seed-density habitats, both before and after pods had dropped from tree branches. Bruchid predation was initially low (<2%) in pods on tree branches in both habitats, but increased abruptly to 12% in riparian and 32% in nonriparian exclosures by the third collection date. Bruchid numbers then crashed to below 2% in both habitats, when pods dropped to the ground. B. sahlbergi predation later increased markedly (up to 65%) again at high-pod-density sites. No further increase in predation took place beyond this level. Seed predation by C. serratus was found to be minimal (<5% of seeds infested) throughout the monitoring period. We suggest that seed predation by the bruchids, prior to pod drop and removal by cattle, is insufficient to cause major impacts on A. nilotica populations. Bruchid seed damage is likely to be significant only in situations with low cattle numbers, where cattle cannot remove the majority of fallen seed pods or where cattle are excluded. Exclusion of cattle from some areas within A. nilotica-invaded landscapes to potentially increase bruchid effectiveness is proposed. The demographic impact of optimal A. nilotica seed losses is discussed.     

Germination of native and introduced plants from scats of Fallow Deer (Dama dama) and Eastern Grey Kangaroo (Macropus giganteus) in a south‐eastern Australian woodland landscape

Introduced deer occur in many forests and woodlands in Australia and potentially play an important role in influencing the floristics and structure of these landscapes through eating plants and disseminating seeds. In a glasshouse trial, we tested whether field‐collected scats of Fallow Deer (Dama dama) contained viable plant seeds. Scats of deer obtained from a woodland study area in Kosciuszko National Park, New South Wales, produced seedlings from a range of native and introduced plant species. Forbs and herbs were dominant in these samples, confirming the grazing behaviour of deer at the time scats were collected. Samples of scats from Eastern Grey Kangaroos (Macropus giganteus), collected contemporaneously from the same sites as deer scats, also produced plant germinants. By volume, deer scats produced a greater diversity of plant germinants, including native and weed species, than did kangaroo scats. Although no weed species emanating from deer or kangaroo scats were of national significance, several species were of regional environmental significance, including Common Mullein (Verbascum thapsis), which was only found germinating out of deer scat, Stinkgrass (Eragrostis cilianensis) and Purpletop (Verbena bonariensis). In addition to dispersing viable seeds, Fallow Deer may also influence vegetation structure through their browsing. Further research is necessary to elucidate their respective role in dispersing native and introduced plants as well as any impacts that foraging behaviour might be having on woodland landscapes, to better inform management of the resident deer population.     

Linking frugivore activity to early recruitment of a bird dispersed tree,Eugenia umbelliflora (Myrtaceae) in the Atlantic rainforest

Seed dispersal by animals is a complex process involving several distinct stages: fruit removal by frugivores, seed delivery in different microhabitats, seed germination, seedling establishment, and adult recruitment. Nevertheless, studies conducted until now have provided scarce information concerning the sequence of stages in a plant's life cycle in its entirety. The main objective of this study was to evaluate the immediate consequences of frugivore activity for Eugenia umbelliflora (Myrtaceae) early recruitment by measuring the relative importance of each fruit‐eating bird species on the establishment of new seedlings in scrub and low restinga vegetation in the Atlantic rainforest, Brazil. We conducted focal tree observations on E. umbelliflora trees recording birds' feeding behaviour and post‐feeding movements. We also recorded the fate of dispersed seeds in scrub and low restinga vegetation. We recorded 17 bird species interacting with fruits in 55 h of observation. Only 30% of the handled fruits were successfully removed. From 108 post flight movements of exit from the fruiting trees, 30.6% were to scrub and 69.4% to low restinga forest. Proportion of seed germination was higher in low restinga than in the scrub vegetation. Incorporating the probabilities of seeds' removal, deposition, and germination in both sites, we found that the relative importance of each frugivorous bird as seed dispersers varies largely among species. Turdus amaurochalinus and Turdus rufiventris were the best dispersers, together representing almost 12% probability of seed germination following removal. Our results show the importance of assessing the overall consequence of seed dispersal within the framework of disperser effectiveness, providing a more comprehensive and realistic evaluation of the relative importance of different seed dispersers on plant population dynamics.     

Seed predation of Copaifera langsdorffii (Fabaceae): a tropical tree with supra‐annual fruiting

Seed predation is an important ecological and evolutionary force that directly affects the distribution of plant species. Copaifera langsdorffii is a tropical tree species with supra‐annual fruiting, which has its seeds predated by a specialist endogenous insect (Rynochenus brevicollis: Curculionidae) in the Brazilian savanna. Three hypotheses were addressed: (i) the predator satiation hypothesis, (ii) the resource concentration hypothesis and (iii) the larger seed predation hypothesis. A total of 112 individual C. langsdorffii were monitored monthly from January to August during four consecutive years (from 2008 to 2011) to determine the presence of fruits on each plant. All trees produced fruits in the year 2008, whereas none of them produced flowers or fruits in 2009 or 2010. Moreover, only 65 individuals (58%) marked in 2008 produced fruits in 2011. The number of fruits per plant was approximately 21% greater in 2008 than in 2011, while the percentage of seed predation was 76% greater in 2011, thereby supporting the predator satiation hypothesis. The percentage of seeds predated was not affected by the number of fruits per plant. Therefore, our data did not support the resource concentration hypothesis. Plants producing large seeds experienced more seed predation by R. brevicollis, supporting the larger seed predation hypothesis. In addition, we also observed a positive relationship between seed volume and adult R. brevicollis weight. This study demonstrates the importance of supra‐annual fruiting for increasing survivorship of C. langsdorffii seeds both at the individual and the population level, and suggests that seed predators select plants producing large seeds as a way of increasing the number of offspring.     

Tree seed rain and seed removal,but not the seed bank,impede forest recovery in bracken (Pteridium aquilinum (L.) Kuhn)‐dominated clearings in the African highlands

Considerable areas dominated by bracken Pteridium aquilinum (L.) Kuhn occur worldwide and are associated with arrested forest recovery. How forest recovery is impeded in these areas remains poorly understood, especially in the African highlands. The component processes that can lead to recruitment limitation—including low seed arrival, availability and persistence—are important determinants of plant communities and offer a potential explanation for bracken persistence. We investigated key processes that can contribute to recruitment limitation in bracken‐dominated clearings in the Bwindi Impenetrable National Park, Uganda. We examined if differences in seed rain (dispersal limitation), soil seed bank, or seed removal (seed viability and persistence) can, individually or in combination, explain the differences in tree regeneration found between bracken‐dominated areas and the neighboring forest. These processes were assessed along ten 50‐m transects crossing the forest–bracken boundary. When compared to the neighboring forest, bracken clearings had fewer seedlings (bracken 11,557 ± 5482 vs. forest 34,515 ± 6066 seedlings/ha), lower seed rain (949 ± 582 vs. 1605 ± 335 tree seeds m^?2 year^?1), comparable but sparse soil seed bank (304 ± 236 vs. 264 ± 99 viable tree seeds/m²), higher seed removal (70.1% ± 2.4% vs. 40.6% ± 2.4% over a 3‐day interval), and markedly higher rodent densities (25.7 ± 5.4 vs. 5.0 ± 1.6 rodents per 100 trapping sessions). Camera traps revealed that rodents were the dominant animals visiting the seeds in our seed removal study. Synthesis: Recruitment limitation contributes to both the slow recovery of forest in bracken‐dominated areas, and to the composition of the tree species that occur. Low seed arrival and low persistence of unburied seeds can both explain the reduced density of seedlings found in bracken versus neighboring forest. Seed removal, likely due to rodents, in particular appears sufficient to constrain forest recovery and impacts some species more severely than others.     

Fruit Production and Seed Predation in Two Miombo Woodland Trees in Zambia

During a six year period (1990–1995) fruiting frequency among marked trees and seed production and predispersal predation by beetle larvae of lsoberlinia angolensis and Julbernardia globiflora of the Leguminosae family and Caesalpinoideae subfamily were studied at two dry miombo woodland sites in central Zambia. Fruit production varied from year to year and was not related to annual rainfall. On average I. angolensis trees fruited once every two years while J. globiflora trees fruited once every two and one-half years. Number of fruits per tree was correlated with tree size for both species. In a peak year fruit biomass represented two to four percent of total above ground biomass but for J. globiflora about 5.5 and 4.5 percent of nitrogen and potassium, respectively, were in fruits compared to 0.6 and 1.8 percent for I. angolensis. The lower fruiting frequency in J. globifora was probably related to the depletion of N reserves during a fruiting year which required a longer replenishment period than in I. angolensis. Predispersal seed predation was low for J. globiflora (10%) and very high in I. angolensis (65–85%) and for the latter species predation rate increased from August to November 1991 and significant variations were observed among years and pod types. Seed predation rate was lowest in a peak fruiting year and this observation provides support for the satiation hypothesis. The results of the study also suggest that I. angolensis and J. globiflora may have different regeneration strategies although reproductive allocation in both species was within the range reported for other iteroparous plants.     

Foraging ecology of the South Australian glossy black‐cockatoo (Calyptorhynchus lathami halmaturinus)

The endangered South Australian glossy black‐cockatoo (Calyptorhynchus lathami halmaturinus Mathews 1912) feeds almost exclusively on the seeds of the drooping sheoak (Allocasuarina verticillata), and shows marked preferences for individual trees. This field study investigated foraging ecology and tree selection through observations of foraging birds and measurements of trees and seed cones. The cockatoos spent the vast majority of their foraging time (94%) handling seed cones, and handling behaviour was highly stereotyped. Handling time per cone was correlated primarily with cone size, while seed intake rate was correlated primarily with seed mass per cone. The cockatoos fed mostly in trees with signs of previous feeding. They tended initially to sample trees with large seeds, and to stay for long feeding bouts in trees with high ratios of seed‐to‐cone mass. As a result of these biases, feeding was concentrated in trees with high seed mass per cone. Preferred trees were also larger, with higher ratios of seed‐to‐cone mass and larger seeds containing more lipid and protein. By feeding from selected trees the cockatoos increased both their seed intake rate and the nutritional quality of the seeds ingested, thereby increasing their energy intake rate by an estimated 28%. They did not discriminate against trees that had re‐grown from basal shoots after fires. Insect larvae were present in some seed cones but the cockatoos did not appear to actively seek them. Males foraged 19% more efficiently than females, resulting in greater daily food intake. The characteristics of individual A. verticillata trees that determined the cockatoos’ feeding rates were also correlated with their distribution on a regional scale. This suggests that the distribution of this endangered cockatoo depends not only on the presence of food trees, but also on their regionally varying feeding profitability.     

Comparing methods of weed seed exposure to predators

Several methods of seed exposure are used in seed predation studies, but how these methods influence the results remains poorly studied. In this article, two commonly used methods of seed exposure – seed cards and plasticine trays – were compared in the field and in the laboratory using three species of weed seeds. In the field, cards or trays with seeds were exposed either with or without cages to keep vertebrates out and either with or without impermeable roofs to provide protection from the weather. The overall seed retrieval from the control stands varied significantly between the methods of seed exposure, roof treatment and the species of seeds, and the scatter in the seed retrieval increased or decreased monotonically with the temperature or precipitation for some species of seeds. This indicates that the controls were more or less relevant depending on the weather conditions and species. The seed removal from cards varied between the species of seeds. The effect of exclosure cages indicated that invertebrates were the dominant seed predators of Capsella bursa‐pastoris, while in Poa annua and Stellaria media both vertebrates and invertebrates were important. Higher seed removal from plasticine trays compared to seed cards was found for all three species of seeds, and placing roofs over the seeds affected seed removal in C. bursa‐pastoris and P. annua. In the laboratory, seed consumption varied with the method of exposure in 10 out of 12 combinations of seed species and predator (two species of carabids and two species of isopods). The overall tendency was the opposite of the field observations: seed consumption was higher for seeds on filter paper and cards compared to seeds on tin trays. We conclude that seed cards are more convenient for short term studies in the field, while tin trays are useful in laboratory multi‐choice experiments. To measure the realistic consumption of invertebrate predators in the laboratory, filter paper seems to be the best option as it does not present an obstacle to predators eating the seed. Using roofs introduced further bias regarding the estimates of seed removal in the field and thus should be avoided.     

Non‐native fruit trees facilitate colonization of native forest on abandoned farmland

Ecological restoration of abandoned, formerly forested farmland can improve the delivery of ecosystem services and benefit biodiversity conservation. Restoration programs can involve removing isolated, non‐native trees planted by farmers for fruit or wood. As such “legacy” trees can attract seed dispersers and create microclimates that help native seedlings to establish, removing them may actually slow forest recovery. Working on abandoned farmland in Kibale National Park, Uganda, we evaluated the effect of legacy trees on forest recovery by measuring the number, diversity, and biomass of native seedlings and saplings regenerating in plots centered on avocado (Persea americana), mango (Mangifera indica), and Eucalyptus legacy trees compared with adjacent plots without legacy trees. The assemblages of native, forest‐dependent tree species in plots around avocado and mango trees were distinct from each other and from those around eucalyptus and all the near‐legacy plots. In particular, avocado plots had higher stem density and species richness of forest‐dependent species than near‐avocado plots, particularly large‐seeded, shade‐tolerant, and animal‐dispersed species—key targets of many restoration plans. Furthermore, many of the species found in high numbers were among those failing to establish in ongoing large‐scale forest restoration in Kibale. Taken together, our results demonstrate that the legacy trees facilitate the dispersal and establishment of native tree species. Retaining the existing legacy trees for a number of years could usefully complement existing management strategies to restore more biodiverse native forest in degraded lands. However, careful monitoring is needed to ensure that the legacy trees do not themselves establish.     

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.