Do seeds from invasive bromes experience less granivory than seeds from native congeners in the Great Basin Desert?

In part, the enemy release hypothesis of plant invasion posits that generalist herbivores in the non-native ranges of invasive plants will prefer native plants to exotic invaders. However, the extent to which this occurs in natural communities is unclear. Here, I examined the foraging preferences of an important guild of generalist herbivores—granivorous rodents—with respect to seeds from a suite of native and invasive Bromus (“brome”) species at five study sites distributed across?≈?80,000 km² of the Great Basin Desert, USA. By examining only congeners, I accounted for a potentially large source of interspecific variation (phylogenetic relatedness). In general, granivorous rodents removed seeds from native bromes at a 23% higher rate than seeds from invasive bromes, suggesting a preference for native species. This preference was not entirely explained by seed size, and patterns of seed removal were consistent across study sites. These findings suggest that invasive bromes in the Great Basin might experience less rodent granivory than native congeners, which is consistent with a key prediction derived from the enemy release hypothesis.     

Effect of spatial and temporal heterogeneity on granivory in the Monte Desert,Argentina

Abstract An important aspect of arid regions is the spatial heterogeneity resulting from differences among plant communities. There are process differences among different vegetation patches increasing variability in the functioning of the ecosystem. The purpose of this study was to estimate granivory, by studying variation of seed removal rates among patches at the local scale and variation according to seed type. We carried out experiments during four seasons in three plant communities in the Monte Desert, Argentina: ‘peladal’, mesquite forest and creosotebush. Seed trays were offered to ants, birds and rodents. Two types of commercial seeds (sunflower and millet) were used. We found that seed removal rate was significantly different among plant communities, among taxa (birds, ants and murid rodents), and among seasons, and that removal rate was higher for sunflower. Seed removal rates by murid rodents were higher than by birds or ants, and occasionally as high as those found in other deserts. The heterogeneity of seed removal patterns at the local level was as strong as that found between continents. Further studies may show similar local heterogeneity in other deserts of the world.     

Functional extinction of a desert rodent: implications for seed fate and vegetation dynamics

Population declines of once‐abundant species have often preceded understanding of their roles within ecosystems. Consequently, important drivers of environmental change may remain undiagnosed because we simply do not know how species that are now rare or extinct shaped ecosystems in the past. Australia's desert rodents are thought to have little numerical impact on seed fate and vegetation recruitment when compared with ants or with desert rodents on other continents. However most research on granivory by Australian desert rodents has occurred in areas where rodents were rare or functionally extinct. Here we ask if the paradigm that rodents are relatively un‐important granivores in Australian deserts is an artefact of their historical decline. In the Strzelecki Desert, the endangered rodent, Notomys fuscus is rare where introduced mesopredators are abundant but common where dingoes (an apex predator) suppress mesopredator populations. We used foraging trays to compare rates of seed removal for a common shrub (Dodonaea viscosa angustissima hopbush) between areas where N. fuscus, hopbush shrubs and their seedlings were rare and common and found that seed removal was consistently higher where rodents were common and hopbush rare. By excluding ants and rodents from foraging trays we show that ants removed more seeds than rodents where rodents were rare but rodents removed far more seeds than ants where rodents were common. By manipulating rodents’ access to the soil seed‐bank we show that hopbush seeds persisted in greater numbers where rodents were excluded than where they had access. Our results support the hypothesis that granivory by rodents may once have been a far more important process influencing the fate of seeds and shaping plant communities in arid Australia and suggest that dingo extirpation has cascading effects on shrub seeds. Our study highlights that functional extinction of rodents may be an under‐appreciated driver of vegetation change.     

Fire and dynamics of granivory on a California grassland forb

This study examines the effects of burning and granivory on the reproductive success of the rare plant Amsinckia grandiflora (Boraginaceae). Fire is often used in California grasslands as a means of exotic species control, but the indirect effects these controls have on the reproductive ecology of native plants are rarely assessed. The interaction of fire with granivory of A. grandiflora seeds was examined in California grasslands over five years (1998–2002). In 1998 and 1999, both burned and unburned plots had bird-exclusion (netted) and no-exclusion (open) treatments. Predation rates were high (51–99%) and final predation rates did not differ among treatments. In 2000, granivory rates in the unburned, open plots were lower than in previous years (14%), and rodent trapping yielded only a single animal. Low granivory rates were observed in 2001 for unburned, open plots (47%). In 2001, burned/open plots experienced significantly more granivory (87%) than either burned/netted plots (37%) or unburned/open plots (47%). In 2002, every seed was taken from burned, open plots. Granivory was highly variable, ranging from 4 to 100% per plot over a 3-week period. Nearly all plots were discovered (>10% predation) by granivores in all trials in all years. When data from all treatments were combined, significant differences in granivory rates occurred among years, indicating stronger inter-year effects than within-year effects due to burning or bird exclusion. Fire affects granivory when overall predation rates are low, but when predation levels are high (as they were in 1998 and 1999), fire may not affect granivory occurring within the same year. Models extending seed survivorship through the dry summer indicate that most seeds are eaten, even when granivory rates are low.     

Effect of seed predation on seed bank size and seedling recruitment of bush lupine (Lupinus arboreus)

Whether seed consumers affect plant establishment is an important unresolved question in plant population biology. Seed consumption is ubiquitous; at issue is whether seedling recruitment is limited by safe-sites or seeds. If most seeds inhabit sites unsuitable for germination, post-dispersal seed consumption primarily removes seeds that would otherwise never contribute to the population and granivory has minimal impacts on plant abundance. Alternatively, if most seeds ultimately germinate before they lose viability, there is greater potential for seed consumption to affect plant recruitment. Of the many studies on seed consumption, few ask how seed loss affects seedling recruitment for species with long-lived seed banks. We examined post-dispersal seed predation and seedling emergence in bush lupine (Lupinus arboreus), a woody leguminous shrub of coastal grasslands and dunes in California. We followed the fate of seeds in paired experimental seed plots that were either protected or exposed to rodent granivores in grassland and dune habitats. Significantly more seeds were removed by rodents in dunes than grasslands. In dunes, where rodent granivory was greatest (65% and 86% of seeds removed from plots by rodents in two successive years), there is a sparse seed bank (6.6 seeds m⁻²), and granivory significantly reduced seedling emergence (in the same two years, 18% and 19.4% fewer seedlings emerged from exposed versus protected plots), suggesting seed rather than safe-site limited seedling recruitment. In contrast, rodents removed an average of 6% and 56% of seeds from grassland plots during the same two years, and the grassland seed bank is 43-fold that of the dunes (288 seeds m⁻²). Even high seed consumption in the second year of the study only marginally influenced recruitment because seeds that escaped predation remained dormant. Burial of seeds in both habitats significantly reduced the percentage of seeds removed by rodents. Results suggest that granivores exert strong but habitat-dependent effects on lupine seed survival and seedling emergence. Received: 24 October 1996 / Accepted: 4 February 1997     

Seed bank dynamics of the desert cactus Opuntia rastrera in two habitats from the Chihuahuan Desert

In desert environments the main input to the seed bank of many succulents is the seed rain through zoochory while high levels of granivory by rodents, birds and ants are the main cause of subsequent losses. In the patchy environment of arid lands the characteristics of both processes may vary between habitats causing differences in the recruitment of new genets. To test this hypothesis we used populations of the desert cactus Opuntia rastrera which has different recruitment rates in the two adjacent habitats where it grows. In Opuntia-dominated scrublands (nopaleras, density ca. 4,000 plants/ha) 1 seedling out of 7,000,000 seeds establish, whereas in grasslands (density ca. 100 plants/ha) this ratio is 1:20,000. From 1996 until 1998 the seed rain, seed removal by granivores and seed abundance in the soil were monitored in both habitats. Results showed striking differences in the dynamics of the seed bank of both habitats. Seed rain was 8.5 times bigger in nopaleras than in grasslands. In nopaleras most seeds were removed by rodents while the quantities of seeds removed by rodents, birds and ants in grasslands were similar. One year after dispersal (the time necessary to break seed dormancy) only 6% of original nopalera seeds and 12% of grassland seeds remained. After germination trials only 1% (ca. 15,000 seeds/ha) and 2% (ca. 2,500 seeds/ha) respectively were viable. These differences in the effective seed bank (6 times bigger in nopaleras) can not explain the differences in genet recruitment (which is several orders of magnitude bigger in grasslands). Apparently the between habitat difference in nurse plant availability and in rodent density (which inflict a strong hervibory upon seedlings) can explain the differences in genet recruitment. It is speculated that this between habitat difference in genet recruitment suggests that the species evolved in less extreme environments (e.g. grasslands) than desert scrublands which, in turn, are colonised due to the singular ability of O. rastrera for vegetative propagation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Invasive earthworms as seed predators of temperate forest plants

Soil seedbanks play a key role in forest plant communities, contributing to regeneration and acting as a refuge from seed predators. This study provides evidence that seeds entering the soil seedbank are vulnerable to granivory by invasive earthworms in temperate forests. Overall, 73 % of seeds of 6 ecologically important forest species were removed from the soil surface over 2 weeks in a Lumbricus terrestris microcosm experiment; 30 % vanished entirely, and presumably were destroyed. The invasive garlic mustard, Alliaria petiolata, was subject to the highest rates of removal. In contrast, results from a field exclosure experiment using 23 species of seed indicate that while seed predation by worms is still detectable, predation by rodents often may mask impacts of earthworms under natural conditions. Worms and rodents preferred different sizes of seeds: while seed predation by rodents was high in mid- to large-seeded species, earthworms tended to prefer smaller seeds. These findings suggest that although rodents are the main driver of seed predation, invasive earthworms may act as an additional ecological filter, and potentially may further influence the species composition of forest plant communities.     

The effect of grazing on granivory patterns in the temperate Monte Desert, Argentina

Structural variations result in a marked heterogeneity of processes in arid environments. Disturbances have noticeable impacts on ecosystems, and a solid way of assessing their effect is to analyze how ecological processes operate. In deserts, granivory has been considered as a keystone process. The objective of our study was to determine the effect of domestic grazing on seed removal rates by birds, ants and rodents as an indirect measure of the process of granivory. This study was carried out in grazed and ungrazed habitats in the central Monte desert ecoregion in Argentina, during February and July 2002. We analyzed three major habitats: mesquite forest, creosotebush shrubland, and sand dunes under two different treatments (grazed, ungrazed). We found significant effects of grazing and non-grazing treatments on total seed removal rates, among granivorous taxa, as well as interactions with season and habitats. Ants and birds were the taxa that differed most under grazing pressure whereas seed removal by rodents showed no significant responses towards grazing. In conclusion, grazing affects plant structure and the assemblage of granivorous taxa, which in turn translates to the granivory process, adding another source of variation to the seed removal patterns reported for the temperate Monte desert.     

Seed predation as a barrier to alien conifer invasions

Interactions between exotic plants and animals can play a major role in determining success or failure of plant introductions. Seed predation has been seen as important in explaining biotic resistance to plant invasion, but this hypothesis has rarely been tested. We studied seed predation on exotic forest plants on an island in Patagonia, Argentina where 43 pine species, including 60% of the world’s known invasive Pinaceae, were introduced ca. 80 years ago, but where exotics attain relatively high densities only near the original plantings. To test if seed predation limits exotic conifer establishment in this area, we compared seed predation in areas close to plantations (colonized by exotics) and far from them (not invaded). Seeds of exotics were preferred over seeds of native species, possibly because exotic seeds are bigger. Predation was more intense in areas far from plantations than in areas close to them, substantially reducing the chances of exotic seed establishment. Using automatic cameras, we found that both rodents and birds preyed on exotic seeds. This study suggests that native seed predators can be an important component of biological resistance to plant invasion.     

Integration of exotic seeds into an Azorean seed dispersal network

Seed dispersal plays a central role in plant ecology. Among animals, birds are particularly important seed dispersers, often incorporating exotic plants into their diets and facilitating their integration in the communities. Network theory offers a highly informative framework to study the structural and functional attributes of complex interactions networks. We used information from bird fecal samples to build a quantitative seed dispersal network for the last fragment of native laurel forest in the island of São Miguel—Azores with three specific objectives: (1) to assess the integration of exotic seeds into seed dispersal; (2) to evaluate the impact of exotic plants in network structure; (3) to test the potential of an exotic species to reduce the seed dispersal of a co-occurring native, via competition for seed dispersers. The seed dispersal network was based on the analysis of 1,121 droppings and described 74 unique interactions between 41 plant species and 7 bird species. Exotic seeds deeply infiltrated into the seed dispersal network forming the majority (59 %) of seeds in the droppings and including those of three globally invasive plants. Overall, birds depended equally on native and exotic fruits despite the lower abundance of the latter in the study area. In an experiment, birds did not show a preference for fruits of the exotic Leycesteria formosa over the native Vaccinium cylindraceum consuming them equally. However, the presence of the exotic plant negatively affected the number of native seeds dispersed, by diverting some of the consumers of the native fruits. Taken altogether the results reveal an alarming invasion level of seed dispersal systems in one of the last remnant native forests of the Azores.     

Granivory in the Chilean matorral: extending the information on arid zones of South America

Comparative studies of granivory intensity across different arid and semi-and regions of the world have assumed homogeneity of conditions over large geographical areas, despite the existence of evident heterogeneities at local and regional scales For South America, previous evidence from the Monte desert, Argentina, showed that granivory intensity is low compared with other continents and that seed removal rates by taxon (granivore ranking) are in decreasing order ants > birds = small mammals In this work, we examined the assumed generality of this pattern for another South American region, the Chilean matorral We studied the differences between sparse and dense habitats of the matorral in granivory intensity throughout the year Although total seed removal did not differ between habitats, differences among granivores did occur Ants were the most important seed removers in both habitats, although they did not differ from birds in the sparse habitat Further, ants were the most important seed consumers during summer, but their seed removal rate is almost negligible the rest of the year Birds maintained an intermediate rate of seed consumption through the year Granivory intensity by small mammals was very low in both habitats during the whole year The granivory ranking obtained for the Chilean matorral was ants > birds > mammals, in dense habitat, and ants = birds > mammals, in sparse matorral Am abundance is correlated with seed removal throughout the year This relationship was not found in the other taxa We discuss possible causes for the differences among habitats, taxa, and seasons, as well as distinct granivore rankings from different continents     

Effects of physical disturbance and granivory on establishment of native and alien riparian trees in Colorado, U.S.A.

Abstract.  In western North America, the alien Elaeagnus angustifolia L. invades riparian habitats usually dominated by pioneer woody species such as Populus deltoides Marshall ssp. monilifera (Aiton) Eckenwalder . We conducted manipulative field experiments to compare the importance of physical disturbance and granivory for seedling establishment of these two species. We planted seeds of both species in disturbed and undisturbed study plots, and used exclosures, seed dish trials and live-trapping to assess the role of granivory. Seedling establishment of both species was increased by physical disturbance and seeds of both species were subject to granivory. However, the relative importance of these two factors differed between species. For P. deltoides , lack of physical disturbance prevented seedling establishment in uncleared subplots, but granivory did not prevent seedling establishment outside of exclosures. For E. angustifolia , granivory prevented seedling establishment outside of exclosures, but lack of physical disturbance did not prevent establishment in uncleared subplots. The lesser dependence on disturbance may enable E. angustifolia to invade areas characterized by low levels of fluvial disturbance, such as floodplains along regulated rivers, where P. deltoides recruitment does not occur. Populations of granivorous rodents may affect the susceptibility of riparian ecosystems to invasion by E. angustifolia .     

Seed removal,seed dispersers,and the allocation of tissues in Myrtaceae seeds

To avoid seed predation, plants may invest in protective seed tissues. Often related to seed size, allocation in seeds' physical defenses can also be influenced by dispersers. We explore the relationships between seed traits (seed mass and hardness) and seed removal in 22 Myrtaceae species of the Brazilian Atlantic Forest, a dominant and diverse fleshy-fruited taxon dispersed by birds, rodents, and other mammals. Our goal is to understand how seed traits influence seed removal rates, and whether dispersers can affect tissue allocation in the seed coat. Seeds were exposed to field removal experiments. In the laboratory, total seed mass and seed coat mass were obtained. To evaluate the influence of seed traits on removal, we performed Kruskal–Wallis and Simple Linear Regression tests. We assessed seed coat and seed mass covariation through standardized major-axis allometric regressions. Harder seeds were larger than softer ones. Seed traits affect removal rates, as tougher and heavier seeds had lower removal. Seed mass significantly predicts seed coat proportion in seven of the 14 species tested. Bird-dispersed species tend to exhibit lower proportions of seed coat as seed mass increases, whereas rodent-dispersed species apparently present the opposite trend, with seed coat proportion increasing with seed mass. Such difference may be caused by the contrasting seed predation pressure represented by birds and rodents. Energy allocation for defense, expressed in seed coat proportion, is greater in large seeds, as these are mostly dispersed by rodents whose propensity to cache and disperse seeds is greater for large and well-protected seeds.     

Resilience of soil seed banks to site degradation in intermittently flooded riverine woodlands

Questions: (1) What is the recovery potential of soil seed banks of intact, average and degraded floodplain woodlands? (2) Will soil seed banks of different functional groups (native and exotic, dryland and wetland) display contrasting responses to site degradation? Location: Semi‐arid, seasonally flooded woodland of eastern Australia. Methods: Diversity, abundance and composition of soil seed banks were assessed using a glasshouse study. Surface soil samples were taken from a total of nine sites with three levels of degradation (intact, average, degraded) from three microsites (sub‐canopy, canopy edge, open). Results: A total of 26 662 individuals of 82 species germinated. Seed abundance increased tenfold from intact to degraded sites, but there was no effect on richness. Species composition of all functional groups varied significantly among degradation states. Seeds of native wetland and exotic dryland species were more abundant in degraded than in intact sites. However, the abundance of native dryland germinants did not differ among degradation classes and no seeds of exotic wetland species were observed. Richness of exotic dryland species was significantly higher in degraded sites. Conclusions: Increasing disturbance promoted seed banks of exotic but not native dryland species and native but not exotic wetland species. Unexpectedly, disturbance promoted the abundance of native seeds more than exotics, although this was driven by a single species. Our results suggest that the dryland phase of the floodplain community is more resilient to degradation than predicted.     

Avian Seed Dispersal of an Invasive Shrub

The incorporation of an animal-dispersed exotic plant species into the diet of native frugivores can be an important step to that species becoming invasive. We investigated bird dispersal of Lonicera maackii, an Asian shrub invasive in eastern North America. We (i) determined which species of birds disperse viable L. maackii seeds, (ii) tested the effect of gut passage on L. maackii seeds, and (iii) projected the seed shadow based on habitat use by a major disperser. We found that four native and one exotic bird species dispersed viable L. maackii seeds. Gut passage through American robins did not inhibit germination, but gut passage through cedar waxwings did. American robins moved mostly along woodlot edges and fencerows, leading us to project that most viable seeds would be defecated in such habitats, which are very suitable for L. maackii. We conclude that L. maackii has been successfully incorporated into the diets of native and exotic birds and that American robins preferentially disperse seeds to suitable habitat.     

小果野芭蕉种子散布和不同时空尺度上种子被捕食格局

 以分布在云南西双版纳地区的大型先锋草本植物小果野芭蕉(Musa acuminata)为研究材料,研究其种子初次散布过程和不同时空尺度上种子被 捕食格局。小果野芭蕉的成熟果实有75%在夜间被取食和传播,在白天消失的果实则占25%。蝙蝠是其最主要的种子传播者,鸟类在其种子传播 过程中也起到一定的作用。人工摆放种子试验结果显示小果野芭蕉种子的主要转移者是小型啮齿类(鼠类)和蚁类：在开放处理下3 d后转移率为 86%,排除蚁类(鼠类可进入)处理下种子转移率为69%以及排除鼠类(蚂蚁可进入)处理下种子被转移率为56%。季节、地点和生境均显著影响人工 摆放种子被转移强度：雨季显著高于旱季(p<0.001), 野芭蕉生境显著高于与其相连的自然森林和荒地(p<0.001),在人为干扰较少的补蚌自然 保护区显著低于西双版纳热带植物园和新山,而后两者之间并无显著差异(p>0.05)。同时,地点和生境以及季节、地点和生境都有显著的交互 作用。与相邻的森林和荒地相比,野芭蕉群落中种子被鼠类捕食的强度最大且受蚁类二次转移的比例最少,森林和荒地中种子被鼠类捕食的强 度相对较小且蚁类对种子的二次转移比例较高,从而更好地帮助种子逃避鼠类捕食。因此,依赖于食果动物(主要是蝙蝠, 也包括鸟类)的初次 散布是小果野芭蕉种子逃避捕食的关键。     

Insects remove more seeds than mammals in first‐year prairie restorations

Seed sowing is a common early step in restoration, but seed consumers can impede plant establishment and alter community structure. Moreover, seed consumers vary in feeding behaviors and the relative importance of different seed consumer groups during restoration are not well understood. At 12 first‐year prairie restorations in Michigan, we studied seed predation using seed removal trays to ask: What is the relative magnitude of seed removal by insects and mammals? Do seed removal rates change over the growing season? Do habitat edges influence seed removal? At what rates are 10 prairie plant species' seeds removed by mammals and insects? Seed removal depended on consumer type, time of year, and seed species. Insects accounted for the majority of seed removal, contrary to previous research in similar systems. In May, insects removed 1.8 times more seeds than mammals, while in August, they removed 5.1 times more. There was greater seed removal in August. During May 28% of seeds were removed, compared to 54% of seeds removed during August, an increase driven by insects. Edge proximity did not influence seed removal. Certain seed species were removed more than others. For example, Lespedeza capitata (round‐headed bush clover) was always removed at high rates, whereas Coreopsis lanceolata (lance‐leaved coreopsis) and Andropogon gerardii (big bluestem) were always removed at low rates. Mammals and insects showed different preferences for several species. This research suggests a prominent role of seed predation, particularly by insects, for early prairie restoration dynamics, with influences varying temporally and among species.     

Mortality of exotic and native seeds in invaded and uninvaded habitats

We examined seed survival in exotic- and native-dominated grasslands by placing seeds of a once-pervasive native grass species, Nassella pulchra, and two of the most common, widespread exotic grass species, Avena fatua and Bromus hordeaceus, in mesh bags in the field for 3 months. Compared to germination of unexposed seeds not placed in the field, exotic species experienced an approximately 40% reduction in viability, whereas the mortality experienced by the native species was <20%. Despite these differences, germination rates of exposed seeds were similar between native and exotic species because native N. pulchra seeds had lower initial viability prior to entering the seed bank. Seed mortality did not differ based on whether seeds were placed in habitats dominated by exotic or native grasses. Rather, our results suggest that re-establishment of native N. pulchra must focus on maximizing seed viability and survival, and that A. fatua and B. hordeaceus overcome relatively higher losses of viable seeds in the seed bank, potentially by producing large numbers of highly viable seeds.     

Incorporating insect infestation into rodent seed dispersal: better if the larva is still inside

Many nutritious seeds are commonly attacked by insects which feed on the seed reserves. However, studies have not fully explored the ecological implications of insect infestation in animal seed dispersal and subsequent plant regeneration. Our question is whether the fact that an infested seed still contains the larva or not might increase/decrease the probability of being successfully dispersed by animals. This study examines the effects of weevil-infested seeds on the natural regeneration of a rodent-dispersed oak species. Rodents showed a high ability to discriminate between sound and infested seeds, even when the larva was still inside. As a result, rodents caused differential seed dispersal for sound and infested seeds by modifying multiple aspects of the dispersal process. We found that, for the same seed weight, infested acorns with a larva still inside can contribute to natural regeneration (0.7?% of seedlings in next summer), although in comparison to sound acorns they suffered higher predation rates by rodents (both partial and complete), were removed later from the ground (less preferred), cached less frequently, and dispersed to shorter distances, which reduced their potential to colonize new environments. However, infested seeds with exit holes are notably less preferred by rodents and, when dispersed, they are mostly deposited on the litter (uncached) with shorter dispersal distances and lower emergence success. Thus, the probability that larval-holed acorns will produce viable seedlings is extremely low (null in this study). Whether infested seeds still contain a larva or not clearly determines the probability of being successfully dispersed. Premature seed drop prolongs the presence of the larva inside the acorn after seed drop, and could be a possible mechanism to allow dispersal of infested seeds.     

Granivory in California sage scrub: implications for common plant invaders and ecosystem conservation

Seed predation may influence community assembly and invasion dynamics when seed predators preferentially select some seed species over others. However, the role of different seed predators and their preferences for seeds in multiple ecological contexts, including the endangered California sage scrub ecosystem, remain unresolved making predictions about which processes limit or promote invasions difficult. In addition, selection criteria, specifically how seed size and biogeographic origin (native versus invasive) influences selection, requires further research across multiple granivore guilds. We examined seed predator preference for common native and invasive seeds across small and large seed classes using seed dish experiments with motion-sensor video observation. We also quantified the relative importance of ants, birds, and mammals as seed predators in sage scrub. Community-wide, granivores preferred the small-seeded invasive mustard Brassica nigra, avoided the large-seeded invasive grass Bromus rubens and the native large-seeded shrub Encelia californica, and did not show significant selection or avoidance for the small-seeded native shrub Salvia apiana. Birds, notably California towhees (Melozone crissalis), were the most frequent granivore while rodents and ants rarely removed seeds. This study reveals that birds are important seed predators in California sage scrub and have the potential to contribute to biotic resistance to mustard invasions (Brassica nigra and potentially others).