Gut Passage Time Research Articles

Digestive efficiencies are independent of gut passage times in rainbow skinks (Trachylepis margaritifer)

Constraints on physiological processes imposed on ectotherms by environmental temperatures can be severe, affecting many aspects of their biology. Included in the suite of physiological processes affected is gut motility, with below optimum temperatures generally resulting in slow gut passage. Trachylepis margaritifer (rainbow skink) however presents an unusual pattern whereby gut passage time decreases at a low temperature compared to when at an intermediate temperature. It has been suggested that this may be a ‘cutting-your-losses’ response whereby nutritional gain is sacrificed by voiding the digesta to reduce the risk of these rotting within the gut at these low temperatures, and if this is so, it should result in reduced digestive performance at 25°C. We tested this hypothesis by measuring appetite, apparent digestive efficiency (ADE) and apparent assimilation efficiency (AAE) in T. margaritifer. We found that although temperature significantly affected appetite and gut passage time, it did not affect digestive efficiency. Both ADE (>90%) and AAE (>80%) were high and temperature-independent across the range tested. Thus, the ‘cutting-your-losses’ hypothesis does not explain faster gut passage at 25°C. High digestive parameters could be maintained by increasing concentrations of digestive enzyme at low temperatures but remains to be tested in this species.

Behavioral and Social Structure Effects on Seed Dispersal Curves of a Forest‐Interior Bulbul (Pycnonotidae) in a Tropical Evergreen Forest

AbstractMovement patterns of animals can vary dramatically as a function of their reproductive cycle or social structure; however, little is known about how changes in the social structure of dispersers affect patterns of seed dispersal. We examined the movement patterns of the forest‐dwelling and cooperatively breeding Puff‐throated Bulbul (Alophoixus pallidus) in relation to different stages of their reproductive cycle, time of day, and group size, to determine potential impacts on the shape and scale of dispersal curves generated using a combination of gut passage time and displacement distance data. There were significant differences in dispersal distances depending on group size, season (breeding, non‐breeding), incubation (vs. other times of the year), and time of the day. The estimated median seed dispersal distance was 28 m. The median dispersal distances produced by birds in larger groups were longer than those of smaller groups (29 m vs. 25 m). During the breeding season, median dispersal distances were longer than during the non‐breeding season (31 m vs. 25 m), but the median dispersal distances were significantly shorter during incubation than during outside incubation (24 m vs. 28 m). The median dispersal distance produced in the early morning (30 m) was also longer than that of other times of the day (23 m late morning, 28 m early afternoon, and 26 m late afternoon). This study suggests that various aspects of an animal's behavior are likely to have significant effects on seed shadows and that this may vary significantly even among individuals of the same species.

Large frugivorous birds facilitate functional connectivity of fragmented landscapes

Summary Quantifying ecosystem functions in spatially explicit ways is important for management decisions in increasingly fragmented landscapes. Between‐patch dispersal of seeds by frugivores constitutes a key ecosystem function to ensure connectivity for fleshy‐fruited plants. However, to date, methodological hurdles have limited our understanding of dispersal pathways on the landscape scale. We made use of newly available tracking devices and combined movement data of 30 trumpeter hornbills Bycanistes bucinator with gut passage times and high‐resolution habitat data in a fragmented forest landscape in South Africa. We identified each potential seed dispersal path and distinguished whether potential seed transport happened to a different forest patch (between‐patch dispersal), within the same patch (within‐patch dispersal) or into the habitat matrix (failed dispersal). To quantify functional landscape connectivity, we identified all possible between‐patch connections and used graph networks to estimate landscape connectivity provided by hornbills. Although potential between‐patch dispersal events were rare (on average 7% compared to 20% failed dispersal and 73% within‐patch dispersal), hornbills could cover distances of up to 15 km. Hornbills visited over 100 forest patches and connected a habitat network with an extent of about 50 km, which increased the potential functional connectivity of the landscape more than twofold. We identified habitat patches that were critical stepping stones for seed dispersal pathways. Without these stepping stones, the network would likely disintegrate into separated components and lead to isolation of forest fragments. Synthesis and applications. We showed that large frugivorous birds can greatly improve functional connectivity for fleshy‐fruited plants across broad scales, linking habitat patches in fragmented forest landscapes. Combining high‐resolution movement and landscape data in graph networks allows identifying seed dispersal pathways and critical stepping stones in fragmented landscapes. This approach addresses the general challenge of spatially explicit mapping of ecosystem services and can be widely incorporated in reserve design and landscape‐level conservation planning.

Patterns of movement and seed dispersal by three lemur species

We combined data on gut-passage times, feeding, and movement to explore the patterns of seed dispersal by Eulemur rubriventer, Eulemur rufrifrons, and Varecia variegata editorum lemurs in Ranomafana National Park, Madagascar. These lemur species deposited less than half of their consumed seeds >100 m away from conspecific trees (40-50%). Long-distance dispersal (>500 m) was rare and average dispersal distances were short relative to those reported of similar-sized haplorrhine primates. The three lemur species showed no significant differences in mean seed-dispersal distances. However, they differed in the shape of their frequency distributions of seed-dispersal distances as a result of differences in how they moved through their habitats. The short distances of seed dispersal we observed and the depauperate frugivorous fauna in Madagascar suggest seed-dispersal may be more limited than in other tropical forests with important implications for plant-community dynamics, biodiversity maintenance, and restoration efforts in Madagascar.

Dioxin and phthalate uptake and assimilation by the green mussel Perna viridis

In this study, the aqueous uptake and dietary assimilation (trophic transfer) of two endocrine disrupting compounds (dioxin and phathalic acid) in the green mussel Perna viridis were quantified. During short-term exposure period, dioxin rapidly sorbed onto phytoplankton and its accumulation was much higher than that of phthalate. The uptake of these two compounds by the mussels increased with increasing temperature and salinity (for dioxin only). The dietary assimilation of the two contaminants was rather modest (10–64% for dioxin and 20–47% for phthalate), and was greatly dependent on the food species and concentration. Interestingly, dietary assimilation increased with increasing diatom food concentration. Gut passage time was partially responsible for the variable dietary assimilation. Given the high dissolved uptake rate and the modest dietary assimilation, aqueous exposure was predicted to be the dominant bioaccumulation source for both dioxin and phthalate in the green mussels under most conditions.

Comparison of four methods to estimate meiobenthic copepod Amonardia normani ingestion rates

Four different methods were used in the control conditions of laboratory to estimate the ingestion rate of a female meiobenthic harpacticoid copepod Amonardia normani: (1) reduction of algal biomass, (2) the quantification of total pigments in fecal pellets, (3) the gut fluorescence method, (4) the percentage of assimilation and the total egestion rate. The food used during all experiments was the diatom Nitzschia constricta in an axenic condition at the concentration of 0.13 μg Chl-a mL−1 at stationary growth phase. All experiments were made at 20 °C and 30 salinity. All tested methods excepted the quantification of total pigments in fecal pellets resulted in similar estimatives. The gut fluorescence method indicated that during the day gut contents are smaller than during the night but the gut passage time was faster, resulting in similar ingestion rates during the day and the night. The reduction of algal biomass and the percentage of assimilation and the total egestion rate also indicated similar ingestion rates in the day and in the night. The daily ingestion rate represents 107 % of female carbon weight per day (903 ng C cop−1day−1).

An introduced species helping another: dispersal of a rose seed infesting wasp by a marsupial in New Zealand

There is little field evidence of fruit-infesting insect species surviving passage through the digestive tract of frugivorous mammal species. In this study, we collected brushtail possum faecal pellets from the wild and demonstrated emergence of adult torymid wasps from Rosa seed without removing the seeds from the pellets. Nineteen percent of possum dung pellets were infested by adult wasps, and a large proportion (85 %) of wasps survived. Survival to emergence was high considering that gut passage time in possums averages 50 h. This period potentially allows greater dispersal distances of wasps than would occur naturally by their own means. This plant–insect-disperser triad was studied in New Zealand where all three species were introduced and did not co-evolve. An exaptation process might have occurred since introduction of these species 150–180 years ago.

Do larger frugivores move seeds further? Body size, seed dispersal distance, and a case study of a large, sedentary pigeon

AbstractAimWorld‐wide declines in large‐bodied frugivores may change seed deposition patterns dramatically if body mass influences seed dispersal‐related traits, such as dispersal distance. We quantified movement patterns and seed dispersal distances by Hemiphaga novaeseelandiae (kereru), the fifth‐largest surviving pigeon world‐wide. We then reviewed how body mass affects seed dispersal distance among fruit‐eating birds globally.LocationTaranaki and Canterbury, New Zealand.MethodsWe radio‐tracked 24 kereru, following each bird continuously for up to 8.5 h, for a total of 43 tracking‐days during the peak fruiting season (February–April). We estimated seed dispersal distances for three fleshy‐fruited species using a mechanistic model based on kereru movements and seed retention times. We analysed global data for volant avian frugivores to determine the effect of body mass on time spent in fruiting trees, seed retention time, and dispersal distance.ResultsKereru were highly sedentary, with an average of 32 ± 39 (mean ± SD) minutes and maximum of 315 minutes between flights. Kereru flew a mean of 77 ± 159 m and maximum of 1457 m in a single flight. They dispersed 66–87% of ingested seeds away from the parent plant. Mean seed dispersal distances for Beilschmiedia tawa, Vitex lucens and Pseudopanax arboreus were 95, 98 and 61 m, respectively, with all species dispersed up to 1469 m. For all three species, 79–88% of seeds were dispersed < 100 m and < 1% were dispersed > 1 km from the parent plant. Globally, both the mean time spent in fruiting trees and seed retention time increased with increasing frugivore body mass. However, retention time increased faster, and therefore the dispersal distance and percentage of seeds moved away from the parent increased with body mass.Main conclusionsDespite sedentary behaviour, kereru disperse many seeds away from the parent plant due to their even longer gut passage time, a function of their large size. Large‐bodied frugivores are disproportionately important as dispersers not only because they can swallow larger fruits, but also because they are more likely to deposit seeds away from the parent plant and at greater distances.

Gut and intestinal passage time in the Rainbow Skink (Trachylepis margaritifer): implications for stress measures using faecal analysis

Stress levels in organisms provide a rapid measure for assessing population health. Handling and capture stress, however, cause error in blood measures, so this method is rapidly being replaced by assessing levels of stress metabolites in faeces. This eliminates the source of error because there is a lag period between stress perception and the resultant stress metabolite accumulation within faeces. This lag period is correlated with specific intestinal passage time, a measure that can vary greatly between taxa, particularly amongst ectotherms. Due to two deleterious consequences associated with extended exposure of the metabolites to the intestinal environment, species that exhibit long and variable intestinal passage times are not good candidates for metabolite studies. We measured gut and intestinal passage times in Trachylepis margaritifer to ascertain whether it would be an appropriate candidate for stress metabolite studies. We first tested if barium sulphate in the meal had an effect on gut passage time at three ambient temperatures (25, 27 and 32 °C). Barium sulphate had no effect; however, temperature had a significant effect with an unexpected pattern: gut passage time was fastest at 32 °C but was slower at 27 °C than at 25 °C. We then used X-ray technology and barium sulphate-loaded meals to measure gut and intestinal passage times at 25 and 27 °C. This allowed us to observe which parts of the digestive process were responsible for increased passage times at 27 °C: the faster passage time at 25 °C was due to faster intestinal passage time; there was no difference in gastric emptying time. We assess the species to be a suitable candidate for studies using faeces to measure stress. It is imperative however, that the effect of temperature on passage rates is known and taken into account in such studies.

Dietary bioavailability of cadmium, inorganic mercury, and zinc to a marine fish: Effects of food composition and type

Elevated metal burdens in farmed fish can pose potential risks to public health as a result of fish consumption. It has been recognized that dietary exposure is a dominant route for metal accumulation in fish. In this study, we first assessed the metal contamination in commercial fish diet and its raw materials. Squid viscera meal, kelp meal and rapeseed meal had metal-specific contamination and contributed to high metal levels in commercial fish diet. We then quantified the metal assimilation efficiency (AE) in a juvenile marine fish blackhead seabream Acanthopagrus schlegelii using a radiotracer technique to assess the dietary bioavailability of cadmium (Cd), inorganic mercury (Hg(II)), and zinc (Zn). Different sources of protein in artificial diets did not significantly affect the metal AEs, except for Hg(II) from corn meal and Zn from corn meal and rapeseed meal. Generally, metal AEs tended to decrease with increasing dietary metal concentrations. Compared to meso-2,3-dimercaptosuccinic acid (DMSA) and l-cysteine in commercial fish diet, metal additives (i.e., 3000μg Fe/g or 200μg Cu/g) were more influential on metal AEs, probably due to metal competition. The relative bioavailability of metals in natural prey vs. artificial diet was inconsistent and complicated by metal chemical species and gut passage time. Our results indicated that metal contamination in commercial fish diet was probably underestimated in fish aquaculture.

Assimilation efficiency and gut passage time in an African elapid snake, Hemachatus haemachatus

We measured apparent assimilation efficiency (AAE) and gut passage time in the African elapid snake Hemachatus haemachatus under laboratory conditions. AAE was dependent on food type, being 89.8% when snakes were fed frogs and 82.8% when fed mice. Differences in AAE for different meal types could be ascribed to the indigestible hair in mouse meals because differences were lost once this component of the mouse meals was removed from the calculation. AAE did not depend on snake body mass and there was no significant difference between AAE measures made at 20°C and 27°C for mouse meals. Gut passage time was 25% faster at 27°C than at 20°C, but was not affected by food type or snake body mass. Larger meals took longer to digest. Thus, H. haemachatus appears to offset reduced digestive performance at lower temperatures by retaining food in the gut for longer when at lower body temperatures (Tbs). These results fit an emerging pattern in snakes whereby digestive efficiency is generally high and insensitive to Tb over the selected thermal range, but may become dependent at lower Tbs when digestion is eventually arrested. The rate of digestion is highly temperature-sensitive and is fastest in the selected Tb range. Diet appears to affect digestive efficiency owing, mainly, to the presence of indigestible components such as hair. Using a comparative framework, venom does not appear to improve digestion for this species, at least over the temperature range tested, relative to other snake species in the literature.

Does a giant tortoise taxon substitute enhance seed germination of exotic fleshy-fruited plants?

Aims The use of exotic species as taxon substitutes to restore lost ecological interactions is currently hotly debated. Aldabrachelys gigantea giant tortoises have recently been introduced to three islands in the Mascarene archipelago (Ile aux Aigrettes, Round Island and Rodrigues) to resurrect herbivory and seed dispersal functions once performed by extinct giant tortoises. However, potential unintended impacts by frugivore substitutes on native ecosystems, e.g. whether they will facilitate the germination of exotic plant species, are largely unknown. We investigated whether A. gigantea introduced to Rodrigues in 2006 could enhance the germination percentage of four widespread fleshy-fruited exotic species on the island. Using germination trials to forecast unintended impacts that could arise from the introduction of a frugivorous taxon substitute enables conservation managers to limit potential adverse negative interactions before they occur. Methods In germination trials that ran over 4 months, we investigated the effects of ingestion (gut passage and deposition in faeces) by subadult and adult A. gigantea on the germination percentage of four exotic fleshy-fruited plant species introduced to Rodrigues. We fed fruits of these plant species to sub-adult and adult A. gigantea to test how variation in age and size of the frugivore would affect seed germination. Feeding of distinctly coloured plastic pellets together with the fruits allowed us to test for individual tortoise effects on seed germination. Important Findings Ingestion by A. gigantea increased the percentage of seeds germinating of Mimusops coriacea and Lantana camara ,b ut not percentage of germination of Veitchia merrillii or Wikstroemia indica. Seeds were more likely to germinate following ingestion by sub-adult rather than adult tortoises, which may be a consequence of the shorter gut passage time observed for sub-adults. Our results demonstrate that introduced frugivorous taxon substitutes could facilitate germination of exotic and invasive plants and highlight the need for conservation managers to weigh the risk of taxon substitutes potentially facilitating the germination and recruitment of exotic fleshy-fruited plants against the benefit of restoring lost seed dispersal functions of threatened indigenous plants. Our findings also highlight the importance of considering age and size variation in frugivores, in particular in long-lived taxa such as giant tortoises, when studying ingestion effects on the germination performance of plants.

Digestive performance in neonatal Southern Pacific Rattlesnakes (Crotalus oreganus helleri)

Despite significant research on the metabolic characteristics of digestion in adult snakes, the digestive performance of neonatal snakes is poorly characterized. We examined the energetic costs associated with digestion and the energetic profit derived from the first meal eaten by neonatal Southern Pacific Rattlesnakes ( Crotalus oreganus helleri Meek, 1905). Composition of venom of C. o. helleri changes through ontogeny, becoming richer in proteolytic components that are hypothesized by some to enhance the rate of digestion. Therefore, we also investigated whether venom type (proteolytic-component-rich “adult” versus neurotoxin-rich “neonate” venom) affected digestive performance. We examined specific dynamic action (SDA), apparent assimilation efficiency, rate of digestion, and gut passage time in snakes fed prey killed with either “adult” or “neonate” venom at 22 and 30 °C. Although digestion progressed more quickly at 30 °C compared with 22 °C, there were no significant differences in digestion rate or assimilation efficiency owing to venom type; however, our statistical power was limited by small sample size. Despite the lack of “digestive experience”, the apparent assimilation efficiency was remarkably high (mean of 92%) and greater than published values for Crotalinae species. Based on these results, we hypothesize that neonatal C. o. helleri make a big energetic profit from their first meal by digesting efficiently and economically.

Consumption and digestion of suspended microbes by juvenile Pacific white shrimp Litopenaeus vannamei

Microalgae hold a key role in the diet of the world's highest-valued seafood species, Pacific white shrimp Litopenaeus vannamei, but ingestion, digestion, and feeding mechanisms employed for consuming suspended microbes are not well studied. The goal of this work was to determine whether juvenile L. vannamei could consume and digest several microbes of varying sizes and structures in suspended monocultures. Diatoms Thalassiosira weissflogii and Amphiprora sp., eustigmatophyte Nannochloropsis salina, and cyanobacterium Synechococcus bacillarus were chosen based upon their common occurrence in intensive shrimp aquaculture systems. Juvenile 2 g L. vannamei, previously starved for 24 h, were individually stocked in aerated flasks containing axenic monocultures of T. weissflogii, Amphiprora sp., N. salina or S. bacillarus for 15, 30, 60, and 90 min. After designated immersion times, shrimp were dissected for collection of stomach and intestine content samples. Fluorometry was used to measure chlorophyll a (μg/g) within the stomach and intestine contents at each time increment. Counts of intact cells (cells/g) within the stomach and intestine contents were completed for shrimp that had been immersed for 60 min. Shrimp demonstrated a sweeping behavior of the third maxillipeds during submersion in some algal cultures, which led to examination through scanning electron microscope photography. Counts of intact cells and chlorophyll a levels in the stomach and intestine indicated that juvenile shrimp actively ingested and digested T. weissflogii and Amphiprora sp. from suspended monocultures. Diatom consumption and digestion were evident across all immersion times, with increasing levels of chlorophyll a in stomach samples up to but not significantly beyond 60 min, indicating that the experimental time period represented a continuous feeding period and spanned the gut passage time. Shrimp were able to ingest S. bacillarus and N. salina to a very limited degree, but there was no evidence of digestion of these cells. Examination under the scanning electron microscope revealed that the third maxillipeds have net-like setae which could potentially select for microorganism > 10 μm in size. Since this cell size reflected the difference between those cells consumed or not consumed in this study, we hypothesize that these appendages may be used by juvenile L. vannamei to filter food particles. These observations provide valuable insight regarding this shrimp's ability to capture and digest microalgae both within its natural environment and in aquaculture systems.

Variable food absorption by Antarctic krill: Relationships between diet, egestion rate and the composition and sinking rates of their fecal pellets

The kinetics of food processing by zooplankton affects both their energy budgets and the biogeochemical fate of their fecal pellets. We sampled 40 schools of krill across the Scotia Sea during spring, summer and autumn and found that in all 3 seasons, every aspect of their absorption and defecation varied greatly. The C content of fecal pellets varied from 0.85% to 29% of their dry mass (median 9.8%) and C egestion rates varied 75-fold. C:N mass ratios of pellets ranged from 4.9 to 13.2 (median 7.8), higher than values of 3.9 in the krill and 5.4 in their food, pointing to enhanced uptake of N. Pellet sinking rates equated to 27–1218 m d −1 (median 304 m d −1), being governed mainly by pellet diameter (80–600 μm, mean 183 μm) and density (1.038–1.391 g cm −3, mean 1.121 g cm −3). Pellets showed little loss of C or N in filtered seawater over the first 2 days and were physically robust. When feeding rates were low, slow gut passage time and high absorption efficiency resulted in low egestion rates of pellets that were low in C and N content. These pellets were compact, dense and fast-sinking. Conversely, in good feeding conditions much food tended to pass quickly through the gut and was not efficiently absorbed, producing C and N-rich, slow-sinking pellets. Such “superfluous feeding” probably maximises the absolute rates of nutrient absorption. Food composition was also important: diatom-rich diets depressed the C content of the pellets but increased their sinking rates, likely due to silica ballasting. So depending on how krill process food, their pellets could represent both vehicles for rapid export and slow sinking, C and N-rich food sources for pelagic scavengers. C egestion rates by krill averaged 3.4% of summer primary production (and ingestion rates would be 2–10-fold higher than this) so whatever the fate of the pellets, krill are an important re-packager within the food web. While salp pellets tend to sink faster than those of krill, it is the latter that tend to prevail in sediment traps. We suggest that this is because krill schools are more compact, producing “rain showers” of pellets that exceed the capacity of pelagic scavengers to reprocess them.

Asian Tapirs Are No Elephants When It Comes To Seed Dispersal

ABSTRACTThe elimination of the largest herbivores (elephants and rhinoceroses) from many forests in tropical East Asia may have severe consequences for plant species that depend on them for seed dispersal. We assessed the capacity of Malayan tapirs Tapirus indicus—the next largest nonruminant herbivore in the region—as a substitute for the lost megafauna in this role by studying their ability to disperse the seeds of nine fleshy‐fruited plants with seeds 5–97 mm in length. We combined information from feeding trials, germination tests, and field telemetry to assess the effect of tapir consumption on seed viability and to estimate how far the seeds would be dispersed. The tapirs (N=8) ingested few seeds. Seed survival through gut passage was moderately high for small‐seeded plants (e.g., 36.9% for Dillenia indica) but very low for medium‐ (e.g., 7.6% for Tamarindus indica) and large‐seeded (e.g., 2.8% for Artocarpus integer) plants. Mean seed gut passage times were long (63–236 h) and only the smallest seeds germinated afterwards. Using movement data from four wild tapirs in Peninsular Malaysia we estimated mean dispersal distances of 917–1287 m (range=22–3289 m) for small‐seeded plants. Malayan tapirs effectively dispersed small‐seeded plants but acted as seed predators for the large‐seeded plants included in our study, suggesting that they cannot replace larger herbivores in seed dispersal. With the absence of elephants and rhinos many megafaunal‐syndrome plants in tropical East Asia are expected to face severe dispersal limitation problems.

Functional responses of an invasive top predator Mustela erminea to invasive meso-predators Rattus rattus and Mus musculus, in New Zealand forests

Context Management of suites of invasive mammal species can lead to perverse outcomes, such as meso-predator release, or can achieve desirable reductions in the abundance of top-order predators by controlling their prey. Predictive models for predator–prey systems require estimates of predator functional responses, i.e. predation rates as functions of prey density. Aims In New Zealand, estimates of the functional responses of stoats (Mustela erminea) to mice (Mus musculus) and ship (black) rats (Rattus rattus) are required to improve management models for these invasive species. Methods We derived fitted relationships between the presence or absence of mouse or ship-rat remains in stoat guts and corresponding indices of prey abundance in beech and podocarp forests, respectively. To convert field data on stoat-gut contents to minimum kill rates, we used data on feeding activity and estimates of gut-passage time, observed in captive stoats. Key results The most parsimonious fitted curves were Type II functional responses, with a steeper stoat–mouse curve for autumn–winter, indicating a more specialist feeding habit than that in spring–summer. Estimated kill rates of mice per stoat per day reached an asymptote of 1.13 during autumn–winter. Our maximum observed kill rate for spring–summer was 11% less than the extrapolated upper limit of 1.04 mice per stoat per day for New Zealand ecosystems. No asymptote was reached within the limits of the data for the stoat–rat relationship. Conclusions Recent models for trophic interactions between stoats and the primary rodent prey have overestimated kill rates by stoats in forested ecosystems, particularly at very low and very high densities of mice. We show how data on stoat-gut contents can be rescaled to estimate minimum kill rates of rodent prey. Implications The functional-response relationships we have derived can be used to improve modelled predictions of the effects of natural or management-driven perturbations of invasive stoats and their primary rodent-prey populations.

Implications of movement patterns of a dietary generalist for mistletoe seed dispersal

AbstractMistletoes are dispersed primarily by frugivorous birds and have highly aggregated distributions at multiple scales. Mistletoe specialist frugivores have been found to intensify infections within infected hosts and stands, and this is considered the most likely mechanism underlying clumped mistletoe distributions at these scales. How these patchy infections first develop and whether seed dispersers also contribute to aggregated mistletoe distributions at landscape and regional scales have not been evaluated. Here we predict the mistletoe seed shadow of a dietary generalist (spiny‐cheeked honeyeater Acanthagenys rufogularis Aves: Meliphagidae), by combining our observations of movements via radio telemetry with previous data on gut passage times to estimate seed dispersal curves for individual birds. There was considerable variation in movements and inferred seed dispersal between individuals, with non‐breeding birds predicted to regularly transport Amyema quandang (Santalales: Loranthaceae) seeds up to 700 m; well beyond the boundaries of an existing mistletoe infection. As the first work to consider explicitly the distance component of mistletoe seed dispersal by dietary generalists, this study poses further questions about the relative seed dispersal roles of dietary generalists and mistletoe specialists. Moreover, our findings highlight considerable intraspecific variation in movement and foraging behaviour, suggesting gender and reproductive status of birds should be considered explicitly when quantifying seed dispersal services.

Tree visitation and seed dispersal of wild cherries by terrestrial mammals along a human land-use gradient

The role of terrestrial mammals as seed dispersers of fleshy-fruited plants has only rarely been investigated in temperate regions although recent studies underline the importance of these animals for long-distance seed dispersal. Here we examine the potential role of mammals as seed dispersers of wild cherry ( Prunus avium L.) along a gradient of human land-use intensity. We placed camera traps at 21 wild cherry trees to identify the mammal species that visited the trees. We conducted feeding trials to test if the recorded species were legitimate seed dispersers or seed predators and to assess gut passage times. We tested the influence of human land-use intensity by quantifying habitat and landscape structure around the study trees at different spatial scales and analyzing its influence on visitation rates of tree visitors. Red fox ( Vulpes vulpes ), roe deer ( Capreolus capreolus ), wild boar ( Sus scrofa ), marten ( Martes spp.) and badger ( Meles meles ) were identified as seed dispersers of wild cherry, of which wild boar was largely a seed predator. Habitat and landscape structure at local spatial scales (70 m, 500 m radius) had no effect on the total visitation rates of mammals. At larger spatial scales (1.0–10.0 km radius) total visitation rates increased with increasing proportion of extensively used farmland and seminatural habitat in the area. The proportion of forest had no influence on visitation rates. The results suggest that high proportions of extensively used farmland and seminatural habitat increase the visitation and seed dispersal rates of large mammals. Comparing gut passage times with home range sizes and daily travel distances suggests that these mammals have the potential to disperse seeds over long distances and can provide gene flow in fragmented agricultural landscapes. Die Rolle von bodenlebenden Säugetieren als Ausbreiter von Samen fleischiger Früchte wurde in den gemäßigten Breiten nur wenig untersucht, obwohl neuere Studien die Bedeutung dieser Tiere für die Ausbreitung über lange Distanzen unterstreichen. Wir untersuchen die Rolle bodenlebender Säuger als Samenausbreiter der Wildkirsche ( Prunus avium L.) entlang eines Landnutzungsgradienten. Wir stellten Kamerafallen an 21 Untersuchungsbäumen auf, um die baumbesuchenden Säuger zu identifizieren. Wir führten Fütterungsversuche durch, um herauszufinden, ob die beobachteten Arten Samenausbreiter oder Samenprädatoren waren und um die Magen-Darmpassagezeiten abzuschätzen. Um den Einfluss anthropogener Landnutzung auf die Besuchsaktivität der baumbesuchenden Säuger zu testen, wurden Habitat- und Landschaftsstruktur auf verschiedenen räumlichen Maßstäben um die Untersuchungsbäume quantifiziert. Rotfuchs ( Vulpes vulpes ), Reh ( Capreolus capreolus ), Wildschwein ( Sus scrofa ), Marder ( Martes spp.) und Dachs ( Meles meles ) wurden als Samenausbreiter der Wildkirsche identifiziert, wobei Wildschweine meist Samenprädatoren waren. Die Habitat- und Landschaftsstruktur auf lokalem Maßstab (70 m, 500 m Radius) hatte keinen Effekt auf die Gesamt-Besuchsaktivität der Säugetiere an den Kirschbäumen. Auf größerem räumlichen Maßstab (1,0–10,0 km Radius) stieg die Besuchsaktivität mit ansteigendem Anteil an extensiver Landwirtschaft und semi-natürlicher Habitate. Der Anteil an Wald hatte keinen Einfluss auf die Besuchsaktivität der Säuger an Wildkirschbäumen. Diese Ergebnisse lassen vermuten, dass hohe Anteile extensiv landwirtschaftlich genutzter Flächen und semi-natürlichem Habitat die Besuchsaktivität großer Säugetiere erhöhen und damit auch die Samenausbreitung steigern. Der Vergleich von Magen-Darmpassagezeiten, Streifgebietsgrößen und täglich zurückgelegten Strecken legt nahe, dass diese Säuger das Potential haben, Samen über lange Distanzen auszubreiten, und damit den Genfluss in fragmentierten, landwirtschaftlich geprägten Gebieten aufrecht erhalten können.

Anatomical and Physiological Changes Associated with a Recent Dietary Shift in the LizardPodarcis sicula

Dietary shifts have played a major role in the evolution of many vertebrates. The idea that the evolution of herbivory is physiologically constrained in squamates is challenged by a number of observations that suggest that at least some lizards can overcome the putative physiological difficulties of herbivory on evolutionary and even ecological timescales. We compared a number of morphological and physiological traits purportedly associated with plant consumption between two island populations of the lacertid lizard Podarcis sicula. Previous studies revealed considerable differences in the amount of plant material consumed between those populations. We continued the investigation of this study system and explored the degree of divergence in morphology (dentition, gut morphology), digestive performance (gut passage time, digestive efficiency), and ecology (endosymbiont density). In addition, we also performed a preliminary analysis of the plasticity of some of these modifications. Our results confirm and expand earlier findings concerning divergence in the morphology of feeding structures between two island populations of P. sicula lizards. In addition to the differences in skull dimensions and the prevalence of cecal valves previously reported, these two recently diverged populations also differ in aspects of their dentition (teeth width) and the lengths of the stomach and small intestine. The plasticity experiment suggests that at least some of the changes associated with a dietary shift toward a higher proportion of plant material may be plastic. Our results also show that these morphological changes effectively translate into differences in digestive performance: the population with the longer digestive tract exhibits longer gut passage time and improved digestive efficiency.