Seed handling behaviours of native and invasive seed‐dispersing ants differentially influence seedling emergence in an introduced plant

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Orchid seed removal by ants in Neotropical ant‐gardens

• Most plants that inhabit ant‐gardens (AGs) are cultivated by the ants. Some orchids occur in AGs; however, it is not known whether their seeds are dispersed by AG ants because most orchid seeds are tiny and dispersed by wind.
• We performed in situ seed removal experiments, in which we simultaneously provided Azteca gnava ants with seeds of three AG orchid species and three other AG epiphyte species (Bromeliaceae, Cactaceae and Gesneriaceae), as well as the non‐AG orchid Catasetum integerrimum.
• The seeds most removed were those of the bromeliad Aechmea tillandsioides and the gesneriad Codonanthe uleana, while seeds of AG orchids Coryanthes picturata, Epidendrum flexuosum and Epidendrum pachyrachis were less removed. The non‐AG orchid was not removed. Removal values were positively correlated with the frequency of the AG epiphytes in the AGs, and seeds of AG orchids were larger than those of non‐AG orchids, which should favour myrmecochory.
• Our data show that Azt. gnava ants discriminate and preferentially remove seeds of the AG epiphytes. We report for the first time the removal of AG orchid seeds by AG ants in Neotropical AGs.

     

Seasonally different modes of seed dispersal in the prostrate annual, <Emphasis Type="Italic">Chamaesyce maculata</Emphasis> (L.) Small (Euphorbiaceae), with multiple overlapping generations

The modes of seed dispersal in the prostrate annual, Chamaesyce maculata, with multiple overlapping generations were investigated. We found that C. maculata has two modes of seed dispersal; autochory in the summer and myrmecochory in the autumn. Seasonally different modes of seed dispersal have not been known in other plant species. The large proportion of seeds produced in the summer was positioned further than the expanse of the parent plants by automatic mechanical seed dispersal. Therefore, autochory would be effective for avoiding competition between parent and offspring plants. No autochory occurred in the seeds produced in the autumn. The seeds of C. maculata without an elaiosome were dispersed by seed-collecting ants in the autumn. Although 18 ant species in total visited the plants of C. maculata at the 50 sites investigated, only two ant species, Tetramorium tsushimae and Pheidole noda frequently carried the seeds of C. maculata. The low frequency of seeds carried out of the nest by P. noda suggests that the workers of P. noda carry the seeds as food into their nest. So, P. noda might be a less effective seed disperser for C. maculata, corresponding to the effectiveness of seed dispersal by harvester ants. However, T. tsushimae ants frequently carried the seeds into and out of their nest, suggesting that T. tsushimae do not regard the seeds of C. maculata as a food resource. Thus, T. tsushimae may be an effective seed disperser for C. maculata.     

Ant-seed interactions: combined effects of ant and plant species on seed removal patterns

Seed dispersal by ants (i.e. myrmecochory) is usually considered as a mutualism: ants feed on nutritive bodies, called elaiosomes, before rejecting and dispersing seeds in their nest surroundings. While mechanisms of plant dispersal in the field are well documented, the behaviour of the ant partner was rarely investigated in details. Here, we compared in laboratory conditions the foraging behaviour of two ant species, the omnivorous Lasius niger and the insectivorous Myrmica rubra to which seeds of two European myrmecochorous plants (Chelidonium majus and Viola odorata) were given. Ant colonies were simultaneously presented three types of items: entire seeds with elaiosome (SE), seeds without elaiosome (S) and detached elaiosomes (E). The presence of elaiosomes on seeds did not attract workers from a distance since ants first contact equally each type of items. Although ants are mass-recruiting species, we never observed any recruitment nor trail-laying behaviour towards seeds. For ants having contacted seed items, their antennation, manipulation and seed retrieval behaviour strongly varied depending on the species of each partner. Antennation behaviour, followed by a loss of contact, was the most frequent ant-seed interaction and can be considered as a “hesitation” clue. For both plant species, insectivorous Myrmica ants removed items in larger number and at higher speed than Lasius. This fits with the hypothesis of a convergence between odours of elaiosomes and insect preys. For both ant species, the small Chelidonium seeds were retrieved in higher proportion than Viola ones, confirming the hypothesis that ants prefer the higher elaiosome/diaspore-ratio. Thus, in these crossed experiments, the ant-plant pair Myrmica/Chelidonium was the most effective as ants removed quickly almost all items after a few antennations. The presence of an elaiosome body increased the seed removal by ants excepting for Myrmica which retrieved all Chelidonium seeds, even those deprived of their elaiosome. After 24 h, all the retrieved seeds were rejected out of the nest to the refuse piles. In at least half of these rejected items, the elaiosome was discarded by ants. Species-specific patterns and behavioural differences in the dynamics of myrmecochory are discussed at the light of ant ecology. Received 10 September 2007; revised 5 February 2008; accepted 5 March 2008.     

Ant behaviour and seed morphology: a missing link of myrmecochory

Seed dispersal by ants (myrmecochory) is mediated by the presence of a lipid-rich appendage (elaiosome) on the seed that induces a variety of ants to collect the diaspores. When seeds mature or fall onto the ground, these ant species transport them to their nest. After eating the elaiosome, the seed is discarded in nest galleries or outside, in the midden or farther away, where seeds can potentially germinate. The final location of seeds with their elaiosomes removed was evaluated to assess the importance of possible handles (structures that ants can grasp to carry) in transporting ants during re-dispersal experiments of seeds from nests of six species of ants. The results indicate that seeds remained within the nest because the ants were not able to transport them out of the nest. As a consequence of the elaiosome being removed, small ant species could not take Euphorbia characias seeds out of their nests. Only large ant species could remove E. characias seeds from their nests. Attaching an artificial handle to E. characias seeds allowed small ant species to redistribute the seeds from their nests. On the other hand, Rhamnus alaternus seeds that have a natural handle after the elaiosome removal were removed from the nests by both groups of ant species. If a seed has an element that acts as a handle, it will eventually get taken out of the nest. The ants’ size and their mandible gap can determine the outcome of the interaction (i.e. the pattern of the final seed shadow) and as a consequence, could influence the events that take place after the dispersal process.     

Evidence for physiological seed dormancy cycling in the woody shrub Asterolasia buxifolia and its ecological significance in fire‐prone systems

• Dormancy cycling is a key mechanism that contributes to the maintenance of long‐term persistent soil seed banks, but has not been recorded in long‐lived woody shrub species from fire‐prone environments. Such species rely on seed banks and dormancy break as important processes for post‐fire recruitment and recovery.
• We used germination experiments with smoke treatments on fresh seeds and those buried for 1 year (retrieved in spring) and 1.5 years (retrieved the following late autumn) to investigate whether Asterolasia buxifolia, a shrub from fire‐prone south‐eastern Australia with physiologically dormant seeds, exhibited dormancy cycling.
• All seeds had an obligation for winter seasonal temperatures and smoke to promote germination, even after ageing in the soil. A high proportion of germination was recorded from fresh seeds. but germination after the first retrieval was significantly lower, despite high seed viability. After the second retrieval, germination returned to the initial level. This indicates a pattern of annual dormancy cycling; one of the few observations, to our knowledge, for a perennial species. Additionally, A. buxifolia’s winter temperature and smoke requirements did not change over time, highlighting the potential for seeds to remain conditionally dormant (i.e. restricted to a narrow range of germination conditions) for long periods.
• For physiologically dormant species, such as A. buxifolia, we conclude that dormancy cycling is an important driver of successful regeneration, allowing seed bank persistence, sometimes for decades, during fire‐free periods unsuitable for successful recruitment, while ensuring that a large proportion of seeds are available for recruitment when a fire occurs.

     

Economic Injury Level and Economic Threshold as required by Forest Stewardship Council for management of leaf-cutting ants in forest plantations

1. The most commonly used method to control insect pests, such as leaf-cutting ants (LCA) in forest plantations, is the application of chemical insecticides, but their use was forbidden in plantations certified by the Forest Stewardship Council because of their negative effect on the environment.
2. A 5-year derogation of their prohibition was obtained in 2016 in Argentina, on the condition that forestry companies reduce pesticide doses by 5% per year and inform the Economic Injury Level (EIL).
3. The EIL and the Economic Threshold (ET) were estimated for the first time for the Acromyrmex genus in a Salicaceae forestation. As a model, we used the damage caused by the most detrimental LCA species of Argentina (Acromyrmex lundii) in the first, most critical year of a willow plantation (Salix nigra) in the lower basin of the Paraná River.
4. The EIL (8–15 nest/ha) was useful to demonstrate the real magnitude of the damage caused by A. lundii, which justified the need for its control. The ET for profitable production (∼3 nests/ha) would not be operatively applicable in a long-term management program in our study site. This methodology could be extrapolated to other Neotropical forest plantations attacked by Acromyrmex species.

     

Temporal patterns of seed use and availability in a guild of desert ants

ABSTRACT.

• 1 Temporal patterns of seed use were studied from late winter to autumn in three species of seed-harvesting ants in the Sonoran Desert. Measures of effective foraging activity, dietary niche breadth and dietary niche overlaps were obtained each month and were tested for correlation with estimates of the available seed resource.
• 2 Seeds were the only numerically important type of food in the diets of all species.
• 3 The ants partitioned the resource according to both seed species and seed size, although there was considerable overlap.
• 4 Pheidole xerophila had the smallest forager body size and is a specialist on small seeds because it harvested them in greater proportion than their rank in the soils and expanded its diet to larger seeds only when the abundance of small seeds declined.
• 5 When the abundance of the small seeds of Bouteloua barbata decreased, the middle-sized ant, Veromessor pergandei, showed a decrease in foraging activity, increase in niche breadth, and a decrease in overlap with P.xerophila.
• 6 Seed size preferences of V.pergandei did not vary seasonally, except that during the month of highest seed abundance, V.pergandei showed no size preference.
• 7 Pogonomyrmex rugosus was the largest ant; it preferred larger seeds and was inactive when small seeds were most abundant. Seasonal foraging activity and niche parameters were random in relation to seed abundance.
• 8 We suggest that nocturnal foraging by P.rugosus during the summer months was a response to interference with diurnal foraging by either predation frorn horned lizards or competition from V.pergandei.
• 9 Seasonal abundance of small seeds explains most of the seasonal foraging patterns of P.xerophila and V.pergandei. The summertime abundance of larger seeds during years of adequate precipitation may account for the seasonal activity patterns of P.rugosus.

     

Ants climb plants because they cannot swim: ant presence on flowers during the flood season reduces the frequency of floral visitors

1. Seasonal changes in environments may not only affect habitat connectivity but may also affect its use by species and their interactions. Thus, during the flood season, ants are forced to develop survival strategies such as vertical plant migration.
2. According to this, it has been hypothesized that the presence of ants may directly affect plant-pollinator interactions.
3. Thus, we asked the following questions: (i) Are floral visitors of Hyptis brevipes expelled due to ant presence on inflorescences during the flood period? (ii) Is the ant effect mediated by the abundance of ants foraging on inflorescences? And, (iii) Does flower abundance predict the abundance of floral visits and ants?
4. We experimentally sampled 59 H. brevipes plants with and without ants during the flooded season, and observed no differences in flower abundance between ant treatments.
5. The probability of detaining floral visitors on H. brevipes increased with ant abundance and exceeded 50% possible repellency, but the probability of visitor deterrence was not related to flower abundance. Furthermore, the abundance of flowers did not predict the number of ants on H. brevipes individuals or the frequency of floral visits.
6. Consequently, ant repelling effects are pronounced when there are more ants foraging on plants. However, the ant repelling effect can be mitigated when plants flourish all year-round and exhibit higher concentrations of flowers in the dry months. Additionally, the different sexual functions of plants may present specific responses due to the explosive pollination mechanism associated with ant effects.

     

UV-B irradiance gradient affects photosynthesis and pigments but not food quality of periphyton

• 1 This laboratory study examined the effect of a gradient of UV‐B radiation (280–320 nm) on photosynthesis and food quality of periphyton, the trophic base of many freshwater benthic communities. Four irradiances of UV‐B (0, 0.6, 1.2, and 2.3 W m^‐2) were delivered by UV‐B lamps (313 nm peak irradiance) over a 13‐day period in the first experiment and over a 4‐h period in the second experiment. These irradiances were roughly equivalent to 0, 1, 2, and 4 times the ambient biologically effective (DNA) midsummer, midday UV‐B irradiance in Tennessee.
• 2 Rates of photosynthesis and photosynthetic pigments were significantly reduced by irradiances greater than ambient during the 13‐day experiment, suggesting that food supply rates to grazers would be depressed by increases in current UV‐B levels. Effects on community structure were minor, but mean diatom cell size decreased at higher UV‐B irradiances.
• 3 Irradiated periphyton was fed in surplus to juvenile snails (Physella gyrina) in the first experiment as a bioassay for food quality. Snail growth was the same on all four diets, suggesting that UV‐B did not affect food quality. Nitrogen and phosphorus content of the periphyton were not affected by UV‐B, either.
• 4 Photosynthesis by low‐biomass periphyton in the second experiment was significantly depressed by irradiances above ambient after only 4 h. Photosynthesis by the high biomass periphyton was not significantly affected by UV‐B, suggesting that self‐shading reduced UV‐B effects.

     

Sperm (ejaculate) competition in Drosophila melanogaster, and the reproductive value of females to males in relation to female age and mating status

• 1 In double mating experiments with Drosophila melanogaster in which one male had been irradiated, it was confirmed that sperm displacement is extensive, i.e. the second male to mate displaces most of the previously-stored sperm.
• 2 The predominance of the second ejaculate over the first increases with the interval between the two matings, from about P₂= 0.83 (second mating on the first day after the first mating) to about P₂= 0.99 (interval between mating = 14 days) where P₂ is the proportion of offspring fathered by the second male.
• 3 A more accurate method for calculating P₂ values is developed for experiments in which sperm are ‘labelled’ by irradiation treatment (equation 1).
• 4 Observations of the reducing egg production of the female throughout life were also obtained. A model is examined which incorporates both the sperm competition and egg production data to predict the reproductive value to a male of a mating with a given type of female, varying in age and mating status. The relative value (in terms of probable numbers of progeny gained) of a mating with a virgin or 4 day post-mating female is about twice that of a 14 day post-mating female, mainly because of the fecundity difference.
• 5 Some evolutionary aspects of sperm competition and multiple mating in insects are reviewed and discussed.

     

Contest competition among Maculinea rebeli butterfly larvae in ant nests

Abstract.

• 1 Caterpillars of the myrmecophilous butterfly Maculinea rebeli showed strong evidence of contest competition when introduced at high densities to laboratory nests of Myrmica ants.
• 2 This is attributed to the direct feeding of caterpillars by workers, which select a few individuals to nurture when food or ant numbers are limiting. It contrasts with published data for a congener, Maculinea arion, which has predacious larvae and experiences scramble competition in crowded ant nests.
• 3 Worker ants from two Myrmica rubra colonies (I and II) were used to found the laboratory nests hosting Maculinea rebeli. Nests from each source reared a similar biomass of Maculinea, but whereas those containing M. rubra I workers reared eight to ten lightweight caterpillars each, cultures from colony II reared half as many caterpillars, each of about double the weight.
• 4 Differences in nest capacity may be due to the different social structures of colonies I and II at the start of the experiment.

     

Social parasite distancing: RADseq reveals high inbreeding in the social parasite Microdon myrmicae but low philopatry for host ant nest

1. The hoverfly Microdon myrmicae is a rare and extremely localised social parasite of Myrmica ants, only occurring around wet grassland. Dispersal, location of the host, and oviposition are crucial steps in the life of ant parasites but are poorly known due to the challenge of studying such rare species.
2. Using genome‐wide loci obtained by RADseq, we investigated the genetic structure and relatedness of Mi. myrmicae larvae and its ant host, collected from three localities in South West England, and inferred biological and behavioural traits.
3. We found that: (a) Mi. myrmicae larvae show high inbreeding levels and severe heterozygosity deficiency, as an expression of the small population size that favours the mating between siblings or half‐siblings; (b) Mi. myrmicae adults can disperse for many kilometres, spreading much more than it is reported for its sibling species, Microdon mutabilis; (c) a single female lays small egg bunches in different ant colonies, sometimes spanning substantial distances (bet‐hedging strategy); in parallel, a single ant nest can harbour eggs from different Microdon females; (d) preliminary evidence suggest that contrary to Mi. mutabilis, host colony choice seems not to depend on the number of queens residing in a single colony.
4. These results overall strongly deviate from what previously found for Mi. mutabilis, whose females oviposit in the natal nest generation after generation. We argue that such different ecological traits and parasitic strategies between closely related species are mainly ascribable to the different selective pressure on the two ant hosts.

     

Phenology of the black bean aphid,Aphis fabae,on organic crops and effect of parasitoid communities

1. Parasitoids represent the third trophic level in plant-insect food webs. They develop in or on herbivorous insects at the second trophic level, which in turn feed on plants that constitute the first trophic level. This food web system might be affected by agricultural landscape and practices.
2. We studied the phenology and population density of Aphis fabae (Hemiptera: Aphididae) and determined the impact of parasitoids in organic fields of beans and beet plants.
3. Twenty leaves per field were collected weekly. For each leaf, the total number of aphids, apterous and alate morphs, the number of mummies, and mortality of aphids were recorded.
4. Our results showed that the phenology of A. fabae varied throughout the season with maximal numbers observed at the beginning of summer. In addition, the production of alate morphs and the proportion of parasitism were positively correlated to an increase in aphid densities.
5. Six parasitoid species were recorded attacking A. fabae in the field, with Lysiphlebus fabarum and Binodoxys angelicae (Hymenoptera: Aphidiinae) being the most abundant parasitoids.
6. Field characteristics and availability of host plants in the surroundings affected A. fabae density. Lysiphlebus fabarum and B. angelicae appeared to be good biocontrol candidates against A. fabae.

     

Indirect effects of alternative food resources in an ant–plant interaction

The seeds of many plant species present a food body that is consumed by animal dispersers. In theory, if the animals are polyphagous, the availability of alternative food resource other than the diaspore itself may influence its dispersal and survival. We used the myrmecochore Helleborus foetidus L. (Ranunculaceae), the seeds of which are attached to a lipid-rich elaiosome that is attractive to ants, as a model system to investigate (1) whether alternative foods that are present along with the plant affect ant foraging behavior and diaspore removal and (2) whether food availability in an ant nest affects seed predation and germination. In a field experiment, artificial diaspore depots were offered together with either sugar, insect corpses, seed, or no food (control). Contrary to the prediction that ants would rather concentrate their foraging effort on the highly rewarding alternative foods only, many workers, attracted by the sugar, switched to the hellebore diaspores, which significantly enhanced removal rate. Results obtained in the laboratory further indicated that the larvae of Aphaenogaster iberica (a major seed disperser) predated more on the H. foetidus embryos when no alternative food was available. This, in turn, slightly reduced seed germination. Overall, these results shed light, for the first time, on the potential indirect effects of alternative resources on the fate of diaspores adapted for ant dispersal.     

Synchronization of the behaviour within nests of the antleptothorax acervorum (fabricius)—I. Discovering the phenomenon and its relation to the level of starvation

Workers of the speciesLeptothorax acervorum show age-polyethism, they start their life as broodworkers and later on they become nestworkers and foragers. Nestworkers and foragers of this ant species are inactive for 72% and 15% of the total time respectively. The short bursts of activity within the nest do not occur randomly but are synchronized so that the whole nest population exhibits nonperiodic pulses of activity: the ants were seen to wake each other actively. In addition starvation experiments were done to assess whether ants react upon food availability. In appeared that during a longlasting period of starvation the proportion of active ants in the nest is at a higher approximately constant level.     

Seasonal patterns in the foraging ecology of the harvester ant Pogonomyrmex naegelii (Formicidae, Myrmicinae) in a Neotropical savanna: daily rhythms, shifts in granivory and carnivory, and home range

The temporal dynamics of foraging, diet, and use of space is essential to understand the ecology of harvester ants. Here, we present an account of the foraging ecology of Pogonomyrmex naegelii in Brazilian cerrado savanna. Nests occur on bare ground and contain 166?C580 workers (N?=?3 colonies). Colony activity is unimodal year-round and peaks around the middle of the day. Foragers leave the nest independently and individually search for food in all directions. Ants ventured up to 15?m from nests, with most foraging occurring within 2?m of nests. Colonies tended to have larger home ranges in the dry/cold (April?CSeptember) than in the wet/warm season (October?CMarch). P. naegelii has a generalist and season-dependent diet comprised of many seed species and arthropod prey, and pieces of plant and animal matter. Foragers collected seeds from 34 plant species, predominantly grasses (genera Gymnopogon, Axonopus, Aristida). Over 6,700 seeds can be stored in nest granaries. Ants and termites were the main animal prey retrieved by P. naegelii. The proportion of seeds and arthropods foraged by P. naegelii changes year-round: in the dry/cold season, the diet is predominantly granivorous, whereas in the wet/warm season, seeds and arthropods are retrieved in more balanced proportions. Although food availability was not assessed, year-round diet of P. naegelii matches the pattern of seasonal abundance of grass seeds and arthropod prey in cerrado. Data on harvester ants come mostly from arid habitats; this study is a first assessment of the ecology of a Neotropical Pogonomyrmex from a moderately moist savanna environment.     

An organic bait based on Palicourea marcgravii (Rubiaceae) and Tephrosia candida (Fabaceae) does not control nests of Atta laevigata (Hymenoptera: Formicidae) in eucalyptus plantations

1. Leaf-cutting ants of the genus Atta (Myrmicinae: Attini) are the main forest pests in Brazil, due to their economic damage, social complexity and geographical distribution. Chemical control with baits is the most viable and successful method to control these insects; and products with low environmental impact have been researched.
2. The objective of this study was to evaluate the mortality of Atta laevigata (Hymenoptera: Formicidae) nests treated with Bioisca® bait, in different dosages, in eucalyptus plantations compared with those treated with sulfluramid and fipronil baits.
3. Seven treatments were used: Bioisca® (Palicourea marcgravii (Rubiaceae) + Tephrosia candida (Fabaceae)), with 5, 10, 15 and 20 g; Blitz® (fipronil), Atta Mex-S® (sulfluramid) baits with 6 g/m² of ant nest loose soil and the control, without ant baits.
4. It took 7 days for the first colony to have its activity stopped using the Blitz® treatment. It happened only at 30 days when treated with Bioisca® and Atta-Mex-S® .
5. The mortality of nests treated with Bioisca® was very low with only one controlled out of 20 that received this bait. Bioisca® does not control the nests of A. laevigata in eucalyptus plantations.

     

Preferential removal of non-injured seeds by an omnivorous ant,Tetramorium tsushimae Emery,in the seed dispersal of Chamaesyce maculata (L.) small

To elucidate roles of an omnivorous ant, Tetramorium tsushimae Emery, against pre-dispersal seed consumers in the seed dispersal of Chamaesyce maculata (L.) Small, the effects of the seed injury by a stinkbug, Nysius plebeius Distat, on the seed removal by the ant and the germination rate were examined in laboratory experiments. The ants of T. tsushimae removed more frequently non-injured seeds than injured seeds. Therefore, low removal frequency of injured seeds by T. tsushimae ants might facilitate the increase in removal frequency of non-injured seeds, consequently leading to efficient seed dispersal of C. maculata. The germination rate of injured seeds that N. plebeius nymphs sucked was conspicuously lower than the non-injured seeds. The germination rate of seeds that T. tsushimae ants carried out of their nest was similar to that of the non-injured seeds. Thus, seed removal by T. tsushimae ants has hardly effects on the germination of these seeds. Therefore, the preferential removal of non-injured seeds by T. tsushimae ants might contribute to the dispersal success of C. maculata seeds. These results might show a novel interaction between myrmecochorous plants and ants in which the assessment of seed quality by ants contributes to the reproductive success of plants.     

TDFCAM: A method for estimating stable isotope trophic discrimination in wild populations

1. Stable isotope mixing models (SIMMs) are widely used for characterizing wild animal diets. Such models rely upon using accurate trophic discrimination factors (TDFs) to account for the digestion, incorporation, and assimilation of food. Existing methods to calculate TDFs rely on controlled feeding trials that are time-consuming, often impractical for the study taxon, and may not reflect natural variability of TDFs present in wild populations.
2. We present TDF_CAM as an alternative approach to estimating TDFs in wild populations, by using high-precision diet estimates from a secondary methodological source—in this case nest cameras—in lieu of controlled feeding trials, and provide a framework for how and when it should be applied.
3. In this study, we evaluate the TDF_CAM approach in three datasets gathered on wild raptor nestlings (gyrfalcons Falco rusticolus; peregrine falcons Falco perigrinus; common buzzards Buteo buteo) comprising contemporaneous δ¹³C & δ¹⁵N stable isotope data and high-quality nest camera dietary data. We formulate Bayesian SIMMs (BSIMMs) incorporating TDFs from TDF_CAM and analyze their agreement with nest camera data, comparing model performance with those based on other relevant TDFs. Additionally, we perform sensitivity analyses to characterize TDF_CAM variability, and identify ecological and physiological factors contributing to that variability in wild populations.
4. Across species and tissue types, BSIMMs incorporating a TDF_CAM outperformed any other TDF tested, producing reliable population-level estimates of diet composition. We demonstrate that applying this approach even with a relatively low sample size (n < 10 individuals) produced more accurate estimates of trophic discrimination than a controlled feeding study conducted on the same species. Between-individual variability in TDF_CAM estimates for ∆¹³C & ∆¹⁵ N increased with analytical imprecision in the source dietary data (nest cameras) but was also explained by natural variables in the study population (e.g., nestling nutritional/growth status and dietary composition).
5. TDF_CAM is an effective method of estimating trophic discrimination in wild animal populations. Here, we use nest cameras as source dietary data, but this approach is applicable to any high-accuracy method of measuring diet, so long as diet can be monitored over an interval contemporaneous with a tissue's isotopic turnover rate.