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

Spatial patterns of seed removal by harvester ants in a seed tray experiment

Using a selection of native grass and forb seeds commonly seeded in local restoration projects, we conducted a field experiment to evaluate the effects of seed species, distance of seed patches from nests, and distance between patches on patterns of seed removal by Owyhee harvester ants, Pogonomyrmex salinus (Olsen) (Hymenoptera: Formicidae). To provide context for ants' seed preferences, we evaluated differences in handling time among seed species. In addition, we assessed the influences of cheatgrass, Bromus tectorum (L.) (Poales: Poaceae), and Sandberg bluegrass, Poa secunda (J. Presl) (Poales: Poaceae), cover on seed removal. We found significant differences in removal rates among seed species. In general, seeds placed closer to nests were more vulnerable to predation than those placed farther away, and seeds in closely spaced patches were more vulnerable than seeds in widely spaced patches. However, the strength of these effects differed by seed species. Differences in handling time among seed species may help to explain these findings; the protective effect of from-nest distance was weaker for species that required less time to transport. For 2 of the seed species, there was an interaction between the distance of seed patches from nests and the distance between patches such that the protective effect of distance between patches decreased as the distance from nests increased. Cheatgrass and bluegrass cover both had small protective effects on seeds. Taken together, these results offer insight into the spatial ecology of harvester ant foraging and may provide context for the successful implementation of restoration efforts where harvester ants are present.

Climate warming increases insect-driven seed removal of two elaiosome-bearing invasive thistle species

Ants and other insects are often a source of localized secondary dispersal for wind-dispersed plants and thus play an important ecological role in their spatial dynamics, but there is limited information on how climate change will affect such dispersal processes. Here, we use field experiments to investigate how climate warming affects seed removal, as this initiation of movement represents the first step in insect-driven secondary dispersal. Our results indicate that for the invasive thistles Carduus nutans and Carduus acanthoides, increased growing temperature influences seed attractiveness to insect dispersers, with seeds from maternal plants grown at temperatures 0.6°C above ambient removed by insect dispersers at higher rates than their unwarmed counterparts. We also observe that seed elaiosomes in these two species play an important role in dispersal, as seeds without elaiosomes were significantly less likely to be removed over the same period. Significant interactions between elaiosome presence/absence and warming treatment were also observed, though only for C. acanthoides, with the boost in seed removal from warming dampened when the elaiosome was present compared to when it was absent. These findings provide evidence that climate warming may alter aspects of dispersal such as seed removal by secondary dispersers, with potential ramifications for dispersal in future climates since seed-bearing plants around the world may be subject to increased growing temperatures, and many of these plant species bear elaiosomes and experience seed dispersal by insects.

Flowering Coriander (Coriandrum sativum) Strips Do Not Enhance Ecosystem Services in Azorean Orchards

The effect of flower strips on ecosystem services (ESs) and disservices (EDs) is routinely assessed following changes in service provider densities without measuring the associated levels of ES/EDs. By using the sentinel approach (i.e., exposing a plant, seeds, and prey models in a standardized way), we tested how coriander (Coriandrum sativum) strips planted in mixed orchards on Terceira Island (Azores, Portugal) affected herbivory on lettuce plants, seed predation on wheat and weed seeds, and predation on artificial caterpillars. Vertebrates had more influence than invertebrates on ESs/EDs. Herbivory (ED) after 2 weeks was similar in the coriander and the control plots (mean ± SD; 2.3% ± 3.3% vs. 2.2% ± 2.9%, n = 32 for both). Seed predation was higher in the control than in the coriander plots for both grain (ED; 30.8% ± 38.9% vs. 15.3% ± 10.8%, n = 18 for both) and weed seeds (ES; 2.5% ± 4.1% vs. 0.4% ± 0.5%, n = 18 for both). Vertebrate predation (ES) rates after 48 h were significantly higher in the control (estimate 9%, 95% CI: 4-20%) than in the coriander plots (3%, 1-8%), while no difference was observed for invertebrate predation. Coriander strips did not support increased ES/reduced ED levels in this setting. The tools used can be effective to quantitatively compare multiple ESs/EDs under different farming management strategies.

Why are some plant species missing from restorations? A diagnostic tool for temperate grassland ecosystems

The U.N. Decade on Ecosystem Restoration aims to accelerate actions to prevent, halt, and reverse the degradation of ecosystems, and re-establish ecosystem functioning and species diversity. The practice of ecological restoration has made great progress in recent decades, as has recognition of the importance of species diversity to maintaining the long-term stability and functioning of restored ecosystems. Restorations may also focus on specific species to fulfill needed functions, such as supporting dependent wildlife or mitigating extinction risk. Yet even in the most carefully planned and managed restoration, target species may fail to germinate, establish, or persist. To support the successful reintroduction of ecologically and culturally important plant species with an emphasis on temperate grasslands, we developed a tool to diagnose common causes of missing species, focusing on four major categories of filters, or factors: genetic, biotic, abiotic, and planning & land management. Through a review of the scientific literature, we propose a series of diagnostic tests to identify potential causes of failure to restore target species, and treatments that could improve future outcomes. This practical diagnostic tool is meant to strengthen collaboration between restoration practitioners and researchers on diagnosing and treating causes of missing species in order to effectively restore them.

Disturbance-Induced Trophic Niche Shifts In Ground Beetles (Coleoptera: Carabidae) In Restored Grasslands

Ecosystem restoration is a critical component of land management, countering the loss of native biodiversity. Restoration efforts are enhanced by reintroducing naturally occurring ecosystem processes, including disturbances that may impact species characteristics such as niche position or niche size. In grasslands, grazing and fire affect plant diversity and habitat complexity, which potentially influence insect dietary behaviors and thus their contributions to functions like seed and arthropod predation. Using carbon and nitrogen stable isotopes, we characterized variation in the dietary niche of six ground beetle species (Coleoptera: Carabidae) in response to grazing by reintroduced bison and prescribed fire disturbances in twenty tallgrass prairies. Management disturbances did not affect activity density for most beetle species and mean trophic position was mostly unaffected. However, five of six species exhibited increased trophic niche area and breadth with disturbances, indicating a switch to a more generalist diet that incorporated a wider range of food items. The combination of bison and fire impacts may increase vegetation patchiness and heterogeneity, driving these diet changes. Morphological traits and microhabitat preferences might mediate response to disturbances and the resulting heterogeneity. Combining prescribed fire and grazing, which increases plant diversity and vegetation structural diversity, may help beetle communities establish over time and support the ecological functions to which these insects contribute.

Seed Predation of Interseeded Cover Crops and Resulting Impacts on Ground Beetles

Interseeding cover crops into standing grains can promote both agronomic and environmental benefits within agroecosystems. Producers must decide which cover crops are the best fit for their goals, and whether diverse cover crop mixtures provide benefits that are worth the increased seed cost. Broadcast seeding is an accessible strategy to try interseeding but can lead to patchy establishment; it is unknown how much seed loss is due to seed predators. In a two-year study, six cover crop species-planted as either single species or mixtures-were interseeded into standing corn. We evaluated seed predation at the time of seeding, agronomic impact through cover crop, and weedy biomass at the end of the season, and conservation impact through activity-density of ground beetles (Coleoptera: Carabidae). Cover crop seeds were vulnerable to seed predation, primarily by vertebrate seed predators, and seed loss varied across cover crop species. Cover crop biomass did not differ according to cover crop diversity and weedy biomass was not affected by cover crop presence or species. Cover crop diversity effects on carabid activity-density were inconsistent: carabids were higher in diverse mixtures in 1 year of the study, but only predicted by vegetative cover, not by cover crop, in the second year. Interseeding cover crops into corn has potential benefits for ground beetles, although the value of mixtures must be further explored.

Effects of management outweigh effects of plant diversity on restored animal communities in tallgrass prairies

A primary goal of ecological restoration is to increase biodiversity in degraded ecosystems. However, the success of restoration ecology is often assessed by measuring the response of a single functional group or trophic level to restoration, without considering how restoration affects multitrophic interactions that shape biodiversity. An ecosystem-wide approach to restoration is therefore necessary to understand whether animal responses to restoration, such as changes in biodiversity, are facilitated by changes in plant communities (plant-driven effects) or disturbance and succession resulting from restoration activities (management-driven effects). Furthermore, most restoration ecology studies focus on how restoration alters taxonomic diversity, while less attention is paid to the response of functional and phylogenetic diversity in restored ecosystems. Here, we compared the strength of plant-driven and management-driven effects of restoration on four animal communities (ground beetles, dung beetles, snakes, and small mammals) in a chronosequence of restored tallgrass prairie, where sites varied in management history (prescribed fire and bison reintroduction). Our analyses indicate that management-driven effects on animal communities were six-times stronger than effects mediated through changes in plant biodiversity. Additionally, we demonstrate that restoration can simultaneously have positive and negative effects on biodiversity through different pathways, which may help reconcile variation in restoration outcomes. Furthermore, animal taxonomic and phylogenetic diversity responded differently to restoration, suggesting that restoration plans might benefit from considering multiple dimensions of animal biodiversity. We conclude that metrics of plant diversity alone may not be adequate to assess the success of restoration in reassembling functional ecosystems.

Smaller and Isolated Grassland Fragments Are Exposed to Stronger Seed and Insect Predation in Habitat Edges

Habitat fragmentation threatens terrestrial arthropod biodiversity, and thereby also leads to alterations of ecosystem functioning and stability. Predation on insects and seeds by arthropods are two very important ecological functions because of their community-structuring effects. We addressed the effect of fragment connectivity, fragment size, and edge effect on insect and seed predation of arthropods. We studied 60 natural fragments of two grassland ecosystems in the same region (Hungarian Great Plain), 30 forest-steppes, and 30 burial mounds (kurgans). The size of fragments were in the range of 0.16–6.88 ha for forest-steppe and 0.01–0.44 ha for kurgan. We used 2400 sentinel arthropod preys (dummy caterpillars) and 4800 seeds in trays for the measurements. Attack marks on dummy caterpillars were used for predator identification and calculation of insect predation rates. In the case of seeds, predation rates were calculated as the number of missing or damaged seeds per total number of exposed seeds. Increasing connectivity played a role only in generally small kurgans, with a negative effect on insect and seed predation rates in the edges. In contrast, fragment size moderated edge effects on insect and seed predation rates in generally large forest-steppes. The difference between edges and centres was more pronounced in small than in large fragments. Our study emphasizes the important role of landscape and fragment-scale factors interacting with edge effect in shaping ecosystem functions in natural grassland fragments of modified landscapes. Managing functional landscapes to optimize the assessment of ecosystem functions and services needs a multispatial scale approach.

Reintroduced grazers and prescribed fire effects on beetle assemblage structure and function in restored grasslands

Ecological restoration seeks to reestablish functioning ecosystems, but planning and evaluation often focus on taxonomic community structure and neglect consumers and their functional roles. The functional trait composition of insect assemblages, which make up the majority of animal diversity in many systems, can reveal how they are affected by restoration management and the consequences for ecosystem function. We sampled ground beetle (Coleoptera: Carabidae) assemblages in restored tallgrass prairies varying in management with prescribed fire and reintroduced American bison (Bison bison) to describe their taxonomic and functional trait structure. We also measured seed and arthropod predation to relate management, beetle assemblage characteristics, and function, and to test if function is maximized by trait diversity, dominant trait values, or beetle abundance. Beetle assemblages primarily varied with restoration age, declining over time in richness and both taxonomic and functional diversity, but bison presence also influenced taxonomic composition. Prescribed fire reduced seed predation in summer and arthropod predation in fall. Although seed predation was unrelated to beetle assemblages, arthropod predation was greater in sites with higher abundances of carnivorous ground beetles. The relatively weak impacts of fire and bison on functional assemblage structure is a promising sign that these management disturbances, aimed at supporting a diverse native plant community, are not detrimental to beetle assemblages. The significance of reduced predator function following prescribed fire will depend on the restoration context and whether seed or arthropod predation relates to management goals.