Gut Passage Time Research Articles

Trophic evolution in ornithopod dinosaurs revealed by dental wear

Ornithopod dinosaurs evolved numerous craniodental innovations related to herbivory. Nonetheless, the relationship between occlusion, tooth wear rate, and tooth replacement rate has been neglected. Here, we reconstruct tooth wear rates by measuring tooth replacement rates and tooth wear volumes, and document their dental microwear. We demonstrate that total tooth volume and rates of tooth wear increased steadily during ornithopod evolution, with deeply-nested taxa wearing up to 3360 mm3 of tooth volume/day. Increased wear resulted in asymmetric tooth crown formation with uneven von Ebner line increment width by the Late Jurassic, and in faster tooth replacement rates in multiple lineages by the mid-Cretaceous. Microwear displays a contrasting pattern, with decreasing complexity and pit percentages in deeply-nested and later-occurring taxa. We hypothesize that early ornithopods were browsers and/or frugivores but deeply nested iguanodontians were bulk-feeders, eating tougher, less nutritious plants; these trends correlate with increasing body mass and longer gut passage times.

The influence of biotic and abiotic factors on the bacterial microbiome of gentoo penguins (Pygoscelis papua) in their natural environment

The microbiome is a key factor in the health, well-being, and success of vertebrates, contributing to the adaptive capacity of the host. However, the impact of geographic and biotic factors that may affect the microbiome of wild birds in polar environments is not well defined. To address this, we determined the bacterial 16S rRNA gene sequence profiles in faecal samples from pygoscelid penguin populations in the Scotia Arc, focusing on gentoo penguins. This mesopredatory group breeds in defined colonies across a wide geographic range. Since diet could influence microbiome structure, we extracted dietary profiles from a eukaryotic 18S rRNA gene sequence profile. The bacterial microbiome profiles were considered in the context of a diverse set of environmental and ecological measures. Integrating wide geographic sampling with bacterial 16S and eukaryotic 18S rRNA gene sequencing of over 350 faecal samples identified associations between the microbiome profile and a suite of geographic and ecological factors. Microbiome profiles differed according to host species, colony identity, distance between colonies, and diet. Interestingly there was also a relationship between the proportion of host DNA (in relation to total 18S rRNA gene signal) and the microbiome, which may reflect gut passage time. Colony identity provided the strongest association with differences in microbiome profiles indicating that local factors play a key role in the microbiome structure of these polar seabirds. This may reflect the influence of local transfer of microbes either via faecal-oral routes, during chick feeding or other close contact events. Other factors including diet and host species also associate with variation in microbiome profile, and in at least some locations, the microbiome composition varies considerably between individuals. Given the variation in penguin microbiomes associated with diverse factors there is potential for disruption of microbiome associations at a local scale that could influence host health, productivity, and immunological competence. The microbiome represents a sensitive indicator of changing conditions, and the implications of any changes need to be considered in the wider context of environmental change and other stressors.

Seed dispersal effectiveness by greater one-horned rhinos and domestic bovids of a megafaunal fruit

The extinction of megafauna, such as rhinos, from tropical Asian forests may have detrimental effects on the regeneration of plant species that rely heavily on their dispersal services. Understanding the potential of other animals to substitute the ecological function of megafauna is important for predicting ecosystem change following declines or extirpation of megafauna. Anthropogenic activities have led to the presence of domestic bovids in many tropical habitats, and these animals could be capable of substituting seed dispersal roles of megafauna. Here, we conducted feeding trials, germination tests, and collected movement data on greater one-horned rhino (Rhinoceros unicornis) and domestic bovids (Bos primigenius; Bubalus bubalis) in the national parks of Chitwan and Shuklaphanta, Nepal. Our aim was to investigate whether domestic bovids can serve as effective substitutes for rhinos in dispersing the megafaunal-fruited Mallotus nudiflorus, which are specialized for rhino dispersal. Specifically, we assessed the long-distance seed dispersal capabilities of rhinos and bovids by combining gut passage times and movement patterns. Additionally, we compared the seed germination success rates among rhinos, bovids and other dispersal modes (e.g., deer and water dispersal). We found that rhinos dispersed 80 percent of seeds over distances greater than 1 km, with potential dispersal distances of up to approximately 5.4 km within their maximum gut passage time. In contrast, cattle dispersed 20 percent of seeds over 1 km, with a maximum distance of around 2.2 km, while buffaloes dispersed 15 percent of seeds over 1 km, with a maximum distance of around 1.4 km. Seeds consumed by rhinos exhibited similar or better germination rates compared to seeds retrieved from cattle and buffalo dung, as well as other dispersal modes. These findings indicate that rhinos provide a functionally unique dispersal service for this megafaunal fruit, especially in long-distance dispersal. While domestic bovids can partially substitute the seed dispersal functions of rhinos, they cannot fully compensate for the loss of seed dispersal that occurs with the disappearance of rhinos.

Effects of thermophily-relevant temperature variation and sex on digestive performance in pythons

Different physiological performances are often optimized at slightly varying temperatures, which can lead to ectotherms selecting higher body temperatures during certain physiological efforts (e.g., digestion, reproduction). Such thermophilic responses can lead to temperature-based tradeoffs between two physiological activities with differing optimal temperatures or between optimizing a physiological activity and water balance, as water loss is elevated at higher temperatures. For example, ectotherms will often select a higher body temperature after consuming a meal, but the extent to which body temperature is elevated after eating is affected by its hydric state. Despite this known hydration state-based suppression of thermophily associated with digestion, the impact of this reduced body temperature on digestion performance is unknown. Accordingly, we determined whether small, thermophily-relevant changes in body temperature impact digestive efficiency or passage time and whether sex influenced the extent of the effect. Eighteen (9 female and 9 male) Children's pythons (Antaresia childreni) each consumed a meal at three temperatures (29 °C, 30 °C, and 31 °C), and gut passage time and digestive efficiency were determined. We found that neither metric was affected by temperature over the range tested. However, digestive efficiency was significantly impacted by the interaction between sex and temperature with males having significantly lower digestive efficiency than females at 31 °C, but not 29 °C or 30 °C. Our results provide insight into the effects of temperature on digestive physiology across narrow temperature ranges as well as demonstrate a sex-based difference in digestive physiology.

Seed dispersal function of the brown bear Ursus arctos on Hokkaido Island in northern Japan: gut passage time, dispersal distance, germination, and effects of remaining pulp.

Megafauna are important seed dispersers because they can disperse large quantities of seeds over long distances. In Hokkaido, Japan, the largest terrestrial animal is the brown bear (Ursus arctos) and other megafauna seed dispersers are lacking. Thus, brown bears are expected to have an important function as seed dispersers in Hokkaido. In this study, we, for the first time, evaluated the seed dispersal function of brown bears in Hokkaido using three fleshy-fruited trees and studied: (1) gut passage time (GPT) in feeding experiments, (2) seed dispersal distance using tracking data of wild bears, and (3) the effect of gut passage and pulp removal on germination rate. Most seeds were defecated intact, and less than 6% were broken. The average GPT without pulp was 3h and 56min to 6h and 13min, depending on the plant and trial. Each plant's average simulated seed dispersal distance was 202-512m. The dispersal distance of Actinidia arguta seeds with pulp was significantly longer than those without pulp because of their longer GPT. The germination rate of defecated seeds without pulp was 19-51%, depending on the plant, and was significantly higher or not different comparing with that of seeds with pulp. We concluded that brown bears in Hokkaido are effective seed dispersers. In managing brown bears in Hokkaido, such ecological functions should be considered along with conserving the bear population and reducing human-bear conflicts.

Gulls contribute to olive seed dispersal within and among islands in a Mediterranean coastal area

AbstractAimTo analyse the role of non‐frugivorous birds on seed dispersal, seed dispersal by gulls is expected to be especially instrumental in island ecosystems, as these have a smaller subset of frugivores when compared to the mainland, and because long‐distance dispersal is required for plant colonisation. Here, we investigated the seed dispersal of olives by gulls among 10 islands of the same archipelago to reveal if gulls contribute to long‐distance seed dispersal including different islands, and how gulls' adaptation to domestic olives and individual differences in foraging activities affect their seed dispersal pattern.LocationBalearic Islands in the Western Mediterranean Sea, Spain.TaxonYellow‐legged gulls (Larus michahellis), Domestic and wild Olives (Olea europaea and O. europaea var. sylvestris).MethodsWe developed seed dispersal models of the two ecotypes of olives dispersed by gulls across an archipelago, based on GPS tracking data, gut passage time and seed viability.ResultsMean dispersal distances were 7.67 (±12.48) km in wild and 12.57 (±13.08) km in domestic olives. 7.1% of wild and 8.5% of domestic olives were dispersed among islands. Among these, 8.2% of domestic seeds were transported from large to small islands where gull colonies are located, whereas wild olives were dispersed in more variable directions. Such dispersal pattern of two olive ecotypes was consistent despite the differences in dispersal distances among individuals.Main ConclusionsGulls contributed to long‐distance olive seed dispersal including different islands. The seed dispersal of domestic olives to longer distances with specific directions may facilitate colonisation and expansion of that variant if the conditions of seed deposition sites are suitable. Our findings indicate that gulls are relevant vectors for long‐distance dispersal of large fleshy fruits in island ecosystems where specialist large frugivores are absent.

Selective ingestion and response by Daphnia magna to environmental challenges of microplastics

Our current understandings of the effects of microplastics and nanoplastics (MNPs) on aquatic animals are predominantly based on the single types of plastic particles. In the present study, we employed the highly fluorescent MNPs that incorporated aggregation-induced emission fluorogens and investigated the selective ingestion and response of Daphnia exposed to different types of plastics at environmentally relevant concentrations simultaneously. When daphnids were exposed to a single MNP, D. magna ingested them instantly in significant amounts. However, even low concentrations of algae had a significant negative impact on the MNP uptake. Specifically, algae caused the MPs to pass through the gut faster, reduced acidification and esterase activity, and changed the distribution of MPs in the gut. In addition, we also quantified the influences of size and surface charge on the selectivity of D. magna. The daphnids selectively ingested larger and positively charged plastics. MPs effectively reduced the uptake of NP and increased its gut passage time. Aggregation of positively and negatively charged MNPs also influenced the gut distribution and increased the gut passage time. The positively charged MPs accumulated in the middle and posterior gut, while aggregation of MNPs also increased acidification and esterase activity. These findings provided fundamental knowledge on the selectivity of MNPs and the microenvironmental responses of zooplankton guts.

The Influence of Seed Characteristics on Seed Dispersal Early Stages by Tibetan Macaques.

Simple SummarySeed dispersal by frugivores is critical to forest regeneration. However, the Tibetan macaque’s seed dispersal function and the effect of seed physical characteristics on seed dispersal effectiveness need to be confirmed. We not only demonstrated that Tibetan macaques could act as seed dispersers, but we also investigated the effect of seed physical characteristics on gut passage time and seed damage rates. Smaller seeds are less likely to be damaged and remain for longer periods of time, whereas larger and heavier seeds are defecated more quickly. In our experiments, the seed-to-shell investment rate had no effect on the damage rate. Understanding the role of seed dispersal in primates can aid in the understanding of seed dispersal symbiosis.There are numerous ecological and evolutionary implications for the ability of frugivores to predate on fruits and consume or disperse their seeds. Tibetan macaques, which are considered important seed predators, typically feed on fruits or seeds. However, systematic research into whether they have a seed dispersal function is still lacking. Endozoochory allows seeds to disperse over greater distances by allowing them to remain in the animal’s digestive tract. Consumption of fruit may not imply effective seed dispersal, and the physical characteristics of seeds (e.g., size, weight, specific gravity, etc.) may influence the dispersal phase’s outcome. We conducted feeding experiments with three captive Tibetan macaques (Macaca thibetana) and nine plant seeds to determine the influence of seed characteristics on Tibetan macaques’ early stages of seed dispersal. The results revealed that the percentage of seed destruction (PSD) after ingestion was 81.45% (range: 15.67–100%), with the PSD varying between plant species. Among the three passage time parameters, the transit time (TT) (mean: 18.8 h and range: 4–24 h) and the time of seed last appearance (TLA) (mean: 100.4 h and range: 48–168 h) differed significantly between seed species, whereas the mean retention time (MRT) (mean: 47.0 h and range: 32–70.3 h) did not. In terms of model selection, PSD was influenced by seed size, weight, volume, and specific gravity; TT was influenced by seed-to-shell investment rate, weight, volume, and specific gravity; and TLA was influenced only by seed size. These findings imply that seeds with a smaller size, specific gravity, volume, and greater weight pass more easily through the monkeys’ digestive tracts. Particularly, seeds with a mean cubic diameter (MCD) of <3 mm had a higher rate of expulsion, larger volume, and weight seeds pass faster, while smaller remained longer. Tibetan macaques, as potential seed dispersers, require specific passage time and passage rates of small or medium-sized seeds. Larger and heavier seeds may be more reliant on endozoochory. Tibetan macaques have the ability to disperse seeds over long distances, allowing for gene flow within the plant community.

The effect of weight and prey species on gut passage time in an endemic gecko Quedenfeldtia moerens (Chabanaud, 1916) from Morocco

Gut passage time (GPT), a key factor in digestive procedure, is of pivotal importance for digestion. Several parameters may affect GPT, such as temperature, length of gastrointestinal tract and body size. Here, we examine the influence of prey weight and prey species on GPT in the endemic diurnal gecko Quedenfeldtia moerens, from the Anti-Atlas Mountains in central Morocco. We used two prey species, house crickets (Acheta domesticus, AD) and mealworms (Tenebrio molitor, TM). Lizards were fed with the larval stage of TM and nymphs of AD. The influence of prey weight and prey species was tested at a constant temperature. We used three weight classes of each prey species to test the influence of prey weight on GPT. Our results showed that prey species affected GPT in a distinct way: mealworms induced a longer gut passage time compared to house crickets. Moreover, GPT increased with the increasing weight of prey for both prey species. Our finding demonstrates that the effect of prey species and prey weight affect digestion and thus should be better clarified in future studies.

Role of siamang (Symphalangus syndactylus) as seed dispersal agent in a Sumatran lowland tropical forest

Abstract. Adyn MF, Sibarani MC, Utoyo L, Surya RA, Sedayu A. 2022. Role of siamang (Symphalangus syndactylus) as seed dispersal agent in a Sumatran lowland tropical forest. Biodiversitas 23: 2101-2110. Seed dispersal is mutualistic interaction between angiosperms and dispersal agents. One of the important dispersers for lowland tropical forests, including in Bukit Barisan Selatan National Park (BBSNP), is siamang (Symphalangus syndactylus Raffles, 1821). This study aimed to determine the seed dispersal pattern, composition of dispersed seeds, and the seed fate dispersed by siamangs at Way Canguk Research Station, BBSNP, Lampung, Indonesia, from February-April 2021. We used the continuous focal sampling method to observe siamang behavior, while the purposive sampling method collected feces and seeds. Siamangs dispersed endozoochory dominantly, all fecal contained seeds, deposited more in the morning, and more scattered than clumped. With a gut passage time of 22.5 ± 3 hours, the seed dispersal distance was 223.9 ± 142 meters from the parents. Seeds &lt; 3 mm were more numerous, but seeds &gt; 3 mm were dispersed more often. Siamang was recorded to disperse a mean of 3.3 ± 1.4 species/feces, and 22 species were dispersed. The germination test showed that only 28% of total planted seeds successfully germinated. Based on in situ monitoring, the remaining deposit sites only accounted for 12% of total records, while the germination rate of dispersed seeds from these deposit sites varied. Further studies are needed with a larger sample to test the consistency of these findings.

Conserved ecophysiology despite disparate microclimatic conditions in a gecko.

Microscale differences in the habitats organisms occupy can influence selection regimes and promote intraspecific variation of traits. Temperature-dependent traits can be locally adapted to climatic conditions or be highly conserved and insensitive to directional selection under all but the most extreme regimes, and thus be similar across populations. The opposing slopes of Nahal Oren canyon in the Carmel Mountains, Israel, are strikingly different: the south-facing slope receives intensive solar radiation, is hot and supports mostly annual vegetation, whereas the north-facing slope is ~10°C cooler, more humid, and supports Mediterranean woodland. We examined whether these differences manifest in the thermal physiology of a common gecko species Ptyodactylus guttatus in controlled laboratory conditions. We predicted that geckos from the hotter south-facing slope would prefer higher temperatures, have faster gut passage times, lower metabolic and evaporative water loss rates, and start diel activity earlier compared with north-facing slope conspecifics. Contrary to these predictions, there were no differences between any of the ecophysiological traits in geckos from the opposing slopes. Nevertheless, our data showed that individuals from the north-facing slope were generally more active in earlier hours of the afternoon compared with south-facing individuals. We suggest that P. guttatus individuals disperse between the slopes and either gene-flow or behavioral plasticity deter local adaptation, resulting in similar physiological traits. Perhaps a stronger contrast in climatic conditions and a stronger barrier are needed to result in interpopulation divergence in temperature-dependent traits.

Long Distance Seed Dispersal by Forest Elephants

By dispersing seeds long distances, large, fruit-eating animals influence plant population spread and community dynamics. After fruit consumption, animal gut passage time and movement determine seed dispersal patterns and distances. These, in turn, are influenced by extrinsic, environmental variables and intrinsic, individual-level variables. We simulated seed dispersal by forest elephants (Loxodonta cyclotis) by integrating gut passage data from wild elephants with movement data from 96 individuals. On average, elephants dispersed seeds 5.3 km, with 89% of seeds dispersed farther than 1 km. The longest simulated seed dispersal distance was 101 km, with an average maximum dispersal distance of 40.1 km. Seed dispersal distances varied among national parks, perhaps due to unmeasured environmental differences such as habitat heterogeneity and configuration, but not with human disturbance or habitat openness. On average, male elephants dispersed seeds farther than females. Elephant behavioral traits strongly influenced dispersal distances, with bold, exploratory elephants dispersing seeds 1.1 km farther than shy, idler elephants. Protection of forest elephants, particularly males and highly mobile, exploratory individuals, is critical to maintaining long distance seed dispersal services that shape plant communities and tropical forest habitat.

Landscape configuration and frugivore identity affect seed rain during restoration

Seed dispersal is a critical ecological function provided largely by vertebrate frugivores in tropical forests. The seed dispersal events mediated by a frugivore species depend on the interaction between the frugivore's traits and landscape structure. Managers seeking to restore seed dispersal to degraded areas to facilitate passive regeneration must consider these interactions. We explore how the relationship between disperser traits and landscape configuration affects seed rain patterns by assessing two restoration goals: 1) high native seed dispersal into degraded areas and 2) low non‐native seed dispersal into intact areas. We developed an individual‐based, spatially‐explicit model, ‘Estimating Seed‐Animal‐Landscape Interactions' (eSALI), and applied it to the case study of Guam, a tropical island that experienced near‐total loss of animal‐mediated seed dispersal following extirpation of its vertebrate frugivores. We focus on two frugivorous bird species, såli Aplonis opaca and totot Ptilinopus roseicapilla, both candidates for rewilding on Guam but differ in their movement distances, gut passage times and habitat use. We simulated populations of both species in seven theoretical landscapes. These landscapes varied in the spatial configuration of intact and degraded forest patches, hosting native and non‐native plant species, respectively. Our results showed that seed rain pattern of the two frugivore species differed across scenarios. A clear tradeoff appeared between both restoration goals in all scenarios: while Såli moved overall more native seeds into degraded areas, they also moved more non‐native seeds into intact areas. Totot on the contrary minimized non‐native seed into intact areas at the expense of moving overall fewer native seeds in degraded areas. This tradeoff was also correlated to landscape configuration: lower heterogeneity minimized non‐native seed rain into intact patches while higher heterogeneity maximized native seed rain into degraded patches. Land managers should explore the interactions between dispersers and landscape configuration to identify ideal candidates for restoring ecological functions.

Mesopredator frugivory has no effect on seed viability and emergence under experimental conditions

AbstractMembers of the orderCarnivoraare a unique and important seed disperser who consume and deposit undamaged seeds while providing regular long‐distance seed dispersal opportunities. Some members ofCarnivora, such as coyotes (Canis latrans), are undergoing range expansions which may help the plant species they consume colonize new locations or replace dispersal services provided by recently extirpated species. In this study, we evaluated aspects of the seed dispersal effectiveness of coyotes and gut passage time to determine the potential dispersal distances for three commonly consumed and commonly occurring plant species (Amelanchier alnifolia, Celtis ehrenbergiana, andJuniperus osteosperma). We also investigated the potential effects of secondary dispersal of seeds away from scats by comparing seedling emergence from whole scats to those where seeds were first removed from scats. We found that seeds generally took between 4 and 24 h to pass through the digestive tract of coyotes, which could result in regular seed dispersal up to 7 km. Gut passage through coyotes had no effect on seed viability or emergence for any of the three plant species, including that gut passage forA. alnifoliaandJ. osteospermadoes not replace cold stratification for breaking physiological dormancy. By simulating secondary dispersal, we found that 22% (±8.2%) moreC. ehrenbergianaseedlings emerged when seeds were removed from scats and those seedlings emerged 7 d earlier (±5 d) compared to seeds that remained in the coyote scat. Coyotes are effective seed dispersers, with the potential for regular long‐distance dispersal services and for providing opportunities for secondary seed dispersal, which could aid in climate migration or serve to replace extirpated dispersal mutualists.

Improved estimation of gut passage time considerably affects trait‐based dispersal models

Abstract Animals are important vectors for transporting seeds, nutrients and microbes across landscapes. However, models that quantify the magnitude of these ecosystem services across a broad range of taxa often rely on generalised mass‐based scaling parameters for gut passage time. This relationship is weak and fundamentally breaks down when considering individual species, indicating that current models may incorrectly attribute or estimate the magnitude of dispersal. We collated a large dataset of gut passage time for endothermic animals measured using undigested markers (n = 391 species). For each species, we compiled trait data, including body mass, morphology, gut physiology, diet and phylogeny. We then compared the ability of five statistical models (constant, generalised least squares, phylogenetic generalised least squares, general linear model and random forest) to estimate the time of first marker appearance (transit time; TT) and mean marker retention time (MRT) for particle and solute markers in mammals and birds separately. For mammals, we found that the inclusion of additional traits appreciably reduced the median root‐mean squared error across all markers in a leave‐one‐out cross validation. For birds, however, additional traits did not significantly improve our ability to predict gut passage time across markers. This may have occurred due to the smaller number of bird species included in our analysis or the absence of important explanatory factors such as differences in gastrointestinal morphology. Using the MRTparticle random forest model from this study, we updated two trait‐based dispersal models for seed and nutrient movement by mammals. The magnitude of dispersal in our updated predictions ranged from 66% to 176% of the original model formulation for different scenarios, highlighting the importance of gut passage time for dispersal models. Furthermore, the contribution by individual or groups of species was found sizeably altered in our updated models. Future modelling studies of dispersal by mammals, for which empirical estimates of gut passage time are absent, will benefit from predicting gut passage time using statistical models that incorporate traits including animal morphology, diet and gut physiology. A free Plain Language Summary can be found within the Supporting Information of this article.

A global meta‐analysis of temperature effects on marine fishes’ digestion across trophic groups

AbstractAimThe temperature constraint hypothesis proposes that marine herbivorous fishes are rare at high latitudes relative to carnivorous fishes because low temperatures impair the digestion of plant material. To test this hypothesis, we compared the effects of temperature on the digestive performance and investment in digestion of marine fishes across trophic groups.LocationGlobal marine ecosystems.Major taxa studiedMarine fishes.MethodsWe analysed data from 304 species consuming a range of diets to quantify the effects of temperature on three indicators of digestive performance and investment: gut passage time, absorption efficiency, and gut length.ResultsDecreasing temperatures increase gut passage time in fishes consuming macroalgae more than fishes consuming other fish or invertebrates. Low temperatures do not impair absorption efficiency in fishes regardless of diet, but herbivores have lower absorption efficiencies than carnivores overall. Gut length decreases with decreasing temperature in all trophic groups.Main conclusionsOur analyses reveal limited evidence to support the temperature constraint hypothesis. Low temperatures slow digestion more in fishes consuming macroalgae than those consuming animal prey; however, this may not reflect a meaningful disadvantage for herbivores but rather could be explained by greater representation of fishes relying on microbial fermentation at high latitudes. Herbivorous fishes absorb nutrients and energy from their food in similar proportions regardless of temperature, in contrast to the expectations of the temperature constraint hypothesis. Decreased gut length was associated with decreasing temperature across all trophic groups, likely due to improved food quality at high latitudes, which should benefit all trophic groups by reducing their required investment in gut tissues. Altogether, our findings run counter to the general hypothesis that low temperatures disadvantage the digestion of plant material and suppress the diversity and abundance of herbivorous fishes at high latitudes.

Frugivory Specialization in Birds and Fruit Chemistry Structure Mutualistic Networks across the Neotropics.

AbstractThe interaction between fruit chemistry and the physiological traits of frugivores is expected to shape the structure of mutualistic seed dispersal networks, but it has been understudied compared with the role of morphological trait matching in structuring interaction patterns. For instance, highly frugivorous birds (i.e., birds that have fruits as the main component of their diets), which characteristically have fast gut passage times, are expected to avoid feeding on lipid-rich fruits because of the long gut retention times associated with lipid digestion. Here, we compiled data from 84 studies conducted in the Neotropics that used focal plant methods to record 35,815 feeding visits made by 317 bird species (155 genera in 28 families) to 165 plant species (82 genera in 48 families). We investigated the relationship between the degree of frugivory of birds (i.e., how much of their diet is composed of fruit) at the genus level and their visits to plant genera that vary in fruit lipid content. We used a hierarchical modeling of species communities approach that accounted for the effects of differences in body size, bird and plant phylogeny, and spatial location of study sites. We found that birds with a low degree of frugivory (e.g., predominantly insectivores) tend to have the highest increase in visitation rates as fruits become more lipid rich, while birds that are more frugivorous tend to increase visits at a lower rate or even decrease visitation rates as lipids increase in fruits. This balance between degree of frugivory and visitation rates to lipid-poor and lipid-rich fruits provides a mechanism to explain specialized dispersal systems and the occurrence of certain physiological nutritional filters, ultimately helping us to understand community-wide interaction patterns between birds and plants.

Gut passage time and viability of seeds consumed by Australian marsupials

Many Australian mammals consume seeds, but their role in seed dispersal has not been well explored. Here, we investigated the mean retention time and the postconsumption germination capacity of Australian seeds (Acacia acuminata, Dodonaea viscosa and Gastrolobium calycinum) likely to be consumed by quenda (Isoodon fusciventer) and woylies (Bettongia penicillata ogilbyi). Mean excretion times were 14h for quenda and 24h for woylies, but some seeds were retained in their digestive passages for up to 39.5 and 55.5h, respectively. Viable seeds of all plant species were retrieved from both species’ scats and only G. calycinum seeds ingested by quenda had a significantly higher germination percentage (62%) than control seeds (34%). Our results show that viable seeds are deposited in the scats of quenda and woylies, indicating that these species may play a role in seed dispersal.

The importance of individual movement and feeding behaviour for long-distance seed dispersal by red deer: a data-driven model

BackgroundLong-distance seed dispersal (LDD) has strong impacts on the spatiotemporal dynamics of plants. Large animals are important LDD vectors because they regularly transport seeds of many plant species over long distances. While there is now ample evidence that behaviour varies considerably between individual animals, it is not clear to what extent inter-individual variation in behaviour alters seed dispersal by animals.MethodsWe study how inter-individual variation in the movement and feeding behaviour of one of Europe’s largest herbivores (the red deer, Cervus elaphus) affects internal seed dispersal (endozoochory) of multiple plant species. We combine movement data of 21 individual deer with measurements of seed loads in the dung of the same individuals and with data on gut passage time. These data serve to parameterize a model of passive dispersal that predicts LDD in three orientations (horizontal as well as upward and downward in elevation).With this model we investigate to what extent per-seed probabilities of LDD and seed load vary between individuals and throughout the vegetation period (May–December). Subsequently, we test whether per-seed LDD probability and seed load are positively (or negatively) correlated so that more mobile animals disperse more (or less) seeds. Finally, we examine whether non-random associations between per-seed LDD probability and seed load affect the LDD of individual plant species.ResultsThe studied deer dispersed viable seeds of at least 62 plant species. Deer individuals varied significantly in per-seed LDD probability and seed loads. However, more mobile animals did not disperse more or less seeds than less mobile ones. Plant species also did not differ significantly in the relationship between per-seed LDD probability and seed load. Yet plant species differed in how their seed load was distributed across deer individuals and in time, and this caused their LDD potential to differ more than twofold. For several plant species, we detected non-random associations between per-seed LDD probability and seed load that generally increased LDD potential.ConclusionsInter-individual variation in movement and feeding behaviour means that certain deer are substantially more effective LDD vectors than others. This inter-individual variation reduces the reliability of LDD and increases the sensitivity of LDD to the decline of deer populations. Variation in the dispersal services of individual animals should thus be taken into account in models in order to improve LDD projections.

Are large frugivorous birds better seed dispersers than medium- and small-sized ones? Effect of body mass on seed dispersal effectiveness.

Frugivorous birds vary in seed dispersal effectiveness (SDE) depending on their body mass. It has been suggested that large birds are more effective dispersers than small ones because they consume a large number of fruits, disperse seeds of distinct sizes, and transport seeds over long distances. Yet, few studies have evaluated the impact of body mass on SDE of birds. In this study, we compiled one database for the quantity (i.e., frequency of visits to plants and number of seeds removed per visit) and quality (i.e., germination of seeds after gut passage and gut retention time of seeds) of seed dispersal by frugivorous birds to evaluate the impact of body mass on SDE. In addition, we compiled data on plant characteristics such as life‐form, fruit type, number of seeds per fruit, and size of seed to evaluate their influence on the quantity and quality of seed dispersal. Data were analyzed with linear mixed effects models and quantile regressions to evaluate the relationship between body mass of birds and quantity, quality, and SDE, in addition to the influence of plant characteristics on SDE. The body mass of birds was negatively related to the frequency of visits to plants. Furthermore, it was positively related to the number of seeds removed per visit, although negatively related to seed size. The life‐form of plants was the only factor explaining the germination of seeds after gut passage. Yet, the body mass of birds was positively related to the gut retention time of seeds. Small and medium birds have a relatively higher SDE than large birds. These results differ from the assertion that large birds are more effective dispersers of plants. Small and medium birds are also effective dispersers of plants that should be preserved and protected from the impact of human activities.