Invertebrate seed predators (ISPs) are an important component of agroecosystems that help regulate weed populations. Previous research has shown that ISPs' seed preference depends on the plant and ISP species. Although numerous studies have quantified weed seed losses from ISPs, limited research has been conducted on the potential for ISPs to consume cover crop seeds. Cover crops are sometimes broadcast seeded, and because seeds are left on the soil surface, they are susceptible to ISPs. We hypothesized that (1) ISPs will consume cover crop seeds to the same extent as weed seeds, (2) seed preference will vary by plant and ISP species, and (3) seed consumption will be influenced by seed morphology and nutritional characteristics. We conducted seed preference trials with four common ISPs [Pennsylvania dingy ground beetle (Harpalus pensylvanicus), common black ground beetle (Pterostichus melanarius), Allard's ground cricket (Allonemobius allardi) and fall field cricket (Gryllus pennsylvanicus)] in laboratory no choice and choice feeding assays. We compared seed predation of ten commonly used cover crop species [barley (Hordeum vulgare), annual ryegrass (Lolium multiflorum), pearl millet (Pennisetum glaucum), forage radish (Raphanus sativus), cereal rye (Secale cereale), white mustard (Sinapis alba), crimson clover (Trifolium incarnatum), red clover (Trifolium pratense), triticale (×Triticosecale) and hairy vetch (Vicia villosa)] and three weed species [velvetleaf (Abutilon theophrasti), common ragweed (Ambrosia artemisiifolia) and giant foxtail (Setaria faberi)]. All four ISPs readily consumed cover crop seeds (P < 0.05), but cover crops with hard seed coats and seed hulls such as hairy vetch and barley were less preferred. Our results suggest that farmers should select cover crop species that are avoided by ISPs if they plan on broadcasting the seed, such as with aerial interseeding.

We used laboratory and field feeding trials to investigate adult carabid beetle preferences for three brassicaceous weed species (rapeseed, wild mustard, and field pennycress) that are pests in canola. All carabid species preferred seeds of rapeseed most and those of field pennycress least and showed intermediate preference for wild mustard seeds. Beetles highly preferred imbibed seeds of all three weed species. Activity–density of carabids and mean weed seed removal were highly correlated in field plots of canola, with activity–density accounting for 67% of the observed variation in seed removal. Our study indicates that seed consumption among carabids is influenced by several factors, including weed species, physiological state of seeds, and carabid activity–density. Carabid seed predation is significant in canola agroecosystems; therefore, understanding these influences has implications for ecological weed management.

Interest in weed seed predation as an ecological weed management tactic has led to a growing number of investigations of agronomic and environmental effects on predation rates. Whereas the measurements in most of these studies have taken place at very short timescales, from days to weeks, measurements at longer timescales (from several months to a year) have greater relevance to the demographic impact of weed seed predation and potential contributions from this process to ecological weed management. Our aim was to quantify the impact of crop phase, within a corn–soybean–wheat crop sequence, on quarterly and annual seed predation rates of giant foxtail, giant ragweed, and velvetleaf. The study took place in areas of the northern U.S. Corn Belt contrasting in dominant land use: Savoy, IL (2005–2007), where corn and soybean production predominates, and East Lansing, MI (2005–2008), where crop production occurs within an old field/forest landscape matrix. Mean annual rates of weed seed predation by the combined action of invertebrate and vertebrate predators were 31 ± 1.6% for giant ragweed, 37 ± 1.4% for velvetleaf, and 53 ± 1.4% for giant foxtail. Crop phase had negligible effects upon long-term seed predation rates, accounting for less than 2% of observed variation. Weed species and site-year, in contrast, contributed 35% and 40%, respectively, of the variation in cumulative annual seed predation. These results are consistent with the spatial variability in best management practices seen at spatial scales greater than the county level: weed seed predation appears to be an inherently site-specific phenomenon. New developments in managing weed seed predation as an ecosystem service are therefore likely to have local recommendation domains or to be driven by stochastic annual variation related to weather or granivore demography.

We determined feeding preferences of invertebrate seed predators and the effect of seed predation on weed emergence. Feeding choice studies were completed with three species of common ground beetles: (Amara aenea DeGeer, Anisodactylus sanctaecrucis F., and Harpalus pensylvanicus DeGeer) (Coleoptera: Carabidae) and the northern field cricket (Gryllus pennsylvanicus DeGeer) (Orthoptera: Gryllidae). Anisodactylus sanctaecrucis, H. pensylvanicus, and the female and male G. pennsylvanicus consumed more redroot pigweed seeds compared with giant foxtail seeds; A. aenea seed consumption did not differ between these two weed species. All invertebrates consumed fewer velvetleaf seeds compared with redroot pigweed and giant foxtail seeds; however, when seed biomass was compared, A. aenea consumed similar biomass of velvetleaf, giant foxtail, and redroot pigweed, whereas A. sanctaecrucis and H. pensylvanicus consumed greater biomass of velvetleaf compared with giant foxtail seed. Seed burial depths of 0.5 or 1.0 cm reduced redroot pigweed and giant foxtail seed consumption by A. aenea and A. sanctaecrucis but not by the larger carabid beetle, H. pensylvanicus. In a greenhouse study, A. sanctaecrucis decreased total weed emergence by 15%, and G. pennsylvanicus females and males decreased weed emergence by 16 and 5%, respectively. Emergence of redroot pigweed, but not velvetleaf or giant foxtail, decreased when A. sanctaecrucis and the male G. pennsylvanicus were present, whereas the emergence of all three weed species decreased in the presence of the female G. pennsylvanicus. In field experiments, vertebrate access to velvetleaf seeds reduced emergence from 4 to 9% across field sites; invertebrate access reduced emergence 4 to 6%. Vertebrate access to giant foxtail seeds reduced emergence 3 to 7%, and invertebrate access reduced emergence 4 to 13%. These results suggest that predation of weed seeds by both vertebrates and invertebrates may reduce weed emergence and influence the weed community.

Ground beetles are postdispersal weed seed predators, yet their role in consuming buried seeds is not well studied. We conducted greenhouse experiments to investigate how seed burial affects consumption of weed seeds (volunteer canola) by adult ground beetles (Coleoptera: Carabidae). Seed burial depth influenced seed consumption rates as demonstrated by a significant interaction between seed burial depth, carabid species, and gender of the carabid tested. We observed higher seed consumption by females of all species, and greater consumption of seeds scattered on the soil surface compared with seeds buried at any depth. However, there was evidence of seed consumption at all depths. Adults of Pterostichus melanarius (Illiger) and Harpalus affinis (Schrank) consumed more buried seeds than did those of Amara littoralis Mannerheim. Agricultural practices, such as tillage, bury seeds at different depths and based on the results of this study, these practices may reduce seed consumption by carabids. Soil conservation practices that reduce tillage (conservation or zero tillage) will favor greater weed seed predation due, in part, to the high availability of seeds at the soil surface or at shallow soil depths.

The potential dispersal of Benghal dayflower seeds by mourning doves was studied in southern Georgia, U.S.A. The gut contents (both crop and gizzard) of mourning doves harvested in the autumn months were investigated to determine if mourning doves fed on Benghal dayflower and whether seeds can survive conditions in the bird gut. Research indicated that mourning doves fed selectively on Benghal dayflower with some harvested birds containing hundreds of Benghal dayflower seeds and capsules in their guts. Further, some seeds recovered remained highly viable. Germination rates in seeds taken from bird crops were similar to controls over the first 4 wk of germination and enhanced over control treatments during the latter 16 wk of a 20-wk germination study. Ultimately, seeds extracted from dove crops had 92% germination as compared to 80% for control seeds. Seeds extracted from dove gizzards had 45% germination, about half that of controls. Benghal dayflower seeds have a structurally reinforced seed coat that probably aids in survival of mechanical damage through bird intestinal tracts. Benghal dayflower seeds exposed to 1.0 M HCl treatment for 2 h had little loss in viability, successfully germinating after such treatment. When evaluating mechanisms for the eradication of Benghal dayflower from agricultural crops, consideration needs to be given to the large number of mourning doves and other bird species that visit cropland and potentially aid in its dispersal.

Granivory can play a pivotal role in influencing regeneration, colonization as well as abundance and distribution of plants. Due to their high abundance, nutrient content and longevity, seeds are an important food source for many animals. Among insects, carabid beetles consume substantial numbers of seeds and are thought to be responsible for a significant amount of seed loss. However, the processes that govern which seeds are eaten and are therefore prevented from entering the seedbank are poorly understood. Here, we assess if DNA-based diet analysis allows tracking the consumption of seeds by carabids. Adult individuals of Harpalus rufipes were fed with seeds of Taraxacum officinale and Lolium perenne allowing them to digest for up to 3 days. Regurgitates were tested for the DNA of ingested seeds at eight different time points post-feeding using general and species-specific plant primers. The detection of seed DNA decreased with digestion time for both seed species, albeit in a species-specific manner. Significant differences in overall DNA detection rates were found with the general plant primers but not with the species-specific primers. This can have implications for the interpretation of trophic data derived from next-generation sequencing, which is based on the application of general primers. Our findings demonstrate that seed predation by carabids can be tracked, molecularly, on a species-specific level, providing a new way to unravel the mechanisms underlying in-field diet choice in granivores.

Parrots represent a large biomass of canopy granivores in tropical forests, and may be effective pre-dispersal seed predators. We evaluated the importance of the lilac-crowned parrot (Amazona finschi) as a pre-dispersal seed predator of Astronium graveolens (Anacardiaceae) in tropical dry forest. Seeds were collected in fruit-traps beneath 22 trees to compare pre-dispersal seed predation by parrots and insects, and determine whether intensity of seed predation was related to fruit-crop size or the aggregation of fruiting conspecifics around focal trees. Ground-level exclosures were established to compare post-dispersal seed predation by vertebrates and insects. The lilac-crowned parrot predated 43% of seeds pre-dispersal, while insects predated only 1.3%. Intensity of pre-dispersal seed predation by parrots was significantly greater in high-fruiting 0.79-ha resource patches, and was not related to fruit abundance of the focal tree. Foraging parrots also discarded immature fruits below the tree, causing a total 56% pre-dispersal loss of seed production, which was greater than post-dispersal removal by vertebrates, mainly rodents (51%) or insects (36%). Our results show that parrots play an important role as pre-dispersal seed predators in tropical dry forests. The reduction of parrot populations in tropical forests may have consequences for seed predation, affecting recruitment patterns of canopy trees.

Seed predation is an important component of seed mortality of weeds in agro-ecosystems, but the agronomic use and management of this natural weed suppression is hampered by a lack of insight in the underlying ecological processes. In this paper, we investigate whether and how spatial and temporal variation in activity-density of granivorous ground beetles (Coleoptera: Carabidae) results in a corresponding pattern of seed predation. Activity-density of carabids was measured by using pitfall traps in two organic winter wheat fields from March to July 2004. Predation of seeds (Capsella bursa-pastoris, Lamium amplexicaule, Poa annua and Stellaria media) was assessed using seed cards at the same sites and times. As measured by pitfall traps, carabids were the dominant group of insects that had access to the seed cards. In the field, predation of the four different species of seed was in the order: C. bursa-pastoris>P. annua>S. media>L. amplexicaule; and this order of preference was confirmed in the laboratory using the dominant species of carabid. On average, seed predation was higher in the field interior compared to the edge, whereas catches of carabids were highest near the edge. Weeks with elevated seed predation did not concur with high activity-density of carabids. Thus, patterns of spatial and temporal variation in seed predation were not matched by similar patterns in the abundance of granivorous carabid beetles. The lack of correspondence is ascribed to effects of confounding factors, such as weather, the background density of seeds, the composition of the carabid community, and the phenology and physiological state of the beetles. Our results show that differences in seed loss among weed species may be predicted from laboratory trials on preference. However, predator activity-density, as measured in pitfall traps, is an insufficient predictor of seed predation over time and space within a field.

Previous studies on several floras have shown that species with small, rounded seeds tend to accumulate persistent seed banks in the soil, while species with larger, less compact seeds do not. The suggested underlying mechanism is predation. Small seeds experience less predation and are more likely to become buried, which itself offers significant protection from predation by vertebrates. The relationship between seed size and shape and persistence in the soil was examined for the flora of the Arasbaran Protected Area in northwest Iran. Seed size was related to persistence in the soil in Iran in the same way as in most other floras examined, but seed shape was not. It is suggested that predation prevents persistence of large seeds in most floras. Where large-seeded persistent species predominate, for example in Australia and (to a lesser extent) in New Zealand, other factors may interfere with the relationship between seed size and predation.

Spatial and seasonal patterns of seed removal by rodents, ants and birds were evaluated using seed-dish experiments in a Trachypogon savanna in Venezuela. Four-day experiments were conducted on three dates and at four different sites. Seeds from 10 native plant species representing a broad mass range were offered at densities equivalent to 3145 seeds m−2. We found that total seed removal and relative importance of granivorous groups varied widely among sites and dates. Rodents were the major seed predators in all the habitats, except for the savanna/forest border where birds dominated. Ants removed more seeds than birds, but since they preferred the smallest seeds, ants ranked last in mass removed. We found a temporally variable relationship between seed removal rates and seed rain or seed bank. We inferred monthly seed predation from seed-dish experiments as well as through the decline of the seed bank in the environment during the dry season, and compared both estimations to evaluate the suitability of the seed-dish technique for estimating granivory. We initially hypothesized that seed-dish experiments that emulate seed availability more closely may yield a better estimate of seed predation, but in fact, they may still overestimate granivory intensity.

Recent data have shown that owing to their seed-predator capacity Chiroderma doriae and Chiroderma villosum trophically depart from all previously studied species within the canopy fruit-bat ensemble. In this paper, the hypothesis that morphological adaptations related to granivory have evolved in these bats is investigated and discussed. A canonical variate analysis was used to search for possible divergent trends between the masticatory apparatus of Chiroderma and other stenodermatines currently recognized in the same ensemble. A total of 142 specimens representative of eight species was included in the analysis. Species of Chiroderma can be discriminated from all other species in the sample based on the increased development of masseter-related variables (height of the anterior zygomatic arch, masseter moment arm, and masseter volume), which, in conjunction with other morphological characteristics (dentition and gape angle) discussed herein, corroborates the evolution of durophagy in this group. A complementary analysis based on a Mantel test revealed that the pattern of morphological differentiation that emerged from the canonical variate analysis does not agree with the one expected based solely on the phylogenetic relationships adopted for the canopy fruit-bats studied here. This result is consistent with the hypothesis that morphological adaptations related to granivory have evolved in Chiroderma.

This study examined whether postdispersal fruit and seed removal by terrestrial mammals of common plant species was affected by the type of item, item density (low, medium, high), and habitat (gap, mid-succession, mature). Fruits of Brosimum alicastrum and Ficus yoponensi (Moraceae), Astrocaryum mexicanum (Palmae), and Nectandra ambigens (Lauraceae), and seeds of Omphalea oleifera (Euphorbiaceae) and Cymbopetalum baillonii (Annonaceae) were tested at the Los Tuxtlas rainforest in Mexico. Item removal from 108 experimental patches (N = 2340 fruits or seeds for each plant species tested) after 5 d was lower for F. yoponensis (6.6%) than for N. ambigens (68.8%), B. alicastrum (67.8%), C. baillonii (64.0%) and A. mexicanum (60.0%). No seeds of O. oleifera were removed. A higher fruit or seed removal was observed from high density than low density food patches in A. mexicanum, C. baillonii and N. ambigens, but not in B. alicastrum and F. yoponensis. A higher fruit or seed removal was observed from food patches in mature forest than in gaps in all plant species tested. Similar removal values between open (open to all terrestrial mammals) and caged (open to small rodents) fruit and seed patches, abundant rodent live-trapping, and a scarcity of large terrestrial mammals, indicated that forest-dwelling small rodents were the main postdispersal removal agents. Differences in plant species seedling recruitment resulting from small rodent food choices can partially determine long-term forest floristic composition at the Los Tuxtlas rainforest.