Year of Publication
Doctor of Philosophy (PhD)
Agriculture, Food and Environment
Dr. David Gonthier
Agricultural intensification and expansion have reduced biodiversity in agroecosystems, jeopardizing the ecosystem services that nature provides to humans in these landscapes including wildlife-mediated pest control. Among these purveyors of ecosystem services are birds, who can provide services to agroecosystems by consuming arthropod pests. Yet some bird species also act as pests by consuming crops. Herein, I use molecular diet analysis through high-throughput sequencing on DNA extracted from bird fecal samples to examine birds’ diet and classify bird species as consumers of major strawberry pests (Lygus spp.). Additionally, I use targeted PCR approaches to determine which bird species consumed strawberries. I then examined how bird diet changed across local and landscape gradients. Then, using multi-species N-mixture models under a Bayesian framework I estimated bird abundance across sites that vary in local diversification and landscape composition. I found that semi-natural habitat at the landscape and farm scale were positively associated with mean abundance of all birds, though effects varied for different species. Further, I found that the mean local abundance of birds classified as Lygus spp.-eaters increased with semi-natural habitat at the farm scale. Additionally, when looking at how bird diet changed across local and landscape gradients, I found that bird diet richness of invertebrates decreased in response to increasing proportions of strawberry in the landscape (500m). Invertebrate diet richness of strawberry-eating birds decreased with both semi-natural habitat in the landscape and strawberry cover in the landscape but increased with crop diversity in the landscape and local weediness. I found that Lygus spp. eaters were more likely to consume Lygus spp. when there was greater local crop diversity (50m) but less likely to do so with greater proportions of local seminatural habitat (50m) and with increasing lengths of fencing and wires at the farm scale. Lygus spp. eaters were more likely to consume strawberry pests with greater local crop diversity. Finally, I found that strawberry eating birds were less likely to consume strawberries in farms with greater surrounding seminatural habitat at the landscape scale. These results suggest that increasing semi-natural habitat at the landscape and local scale can bolster bird conservation across farms. These results, however, also reveal that while Lygus spp. eating birds are promoted by semi-natural habitat at the farm scale, Lygus spp. eating birds are less likely to consume Lygus spp. with greater proportion of semi-natural habitat at the local scale. Thus, here it must be considered whether promoting the abundance of Lygus spp. eaters through local semi-natural vegetation is more important for pest control and outweighs any negative impact that local-seminatural habitat may have on the likelihood of Lygus spp. consuming birds to consume Lygus spp.
Facing a similar fate in the face of agricultural intensification and specialization have been integrated crop-livestock systems, which have become ecologically disintegrated and spatially disconnected as agricultural specialization was facilitated by the wide availability of synthetic inputs such as synthetic fertilizer and the mechanization of farm equipment. Recently, however, there has been a renewed interest in integrated crop-livestock systems and the ecological benefits that they may confer to agroecosystems. While studies investigating the net effects of wild birds in agroecosystems have increased over the last decade, there has been scant attention given to investigating the net effects of pasture-raised poultry agroecosystems. In my dissertation, I investigate the net effects of pasture-raised poultry of varying densities on ground and vegetation-dwelling arthropod communities in a mixed-cover crop system. I found that contrary to the top-down exertion that I expected for chickens to have on all arthropod communities, I found that nutrient deposits (via fecal deposits) may be driving the abundance of ground-dwelling arthropods in this system evidenced by greater abundance of various insect groups in the poultry treatments relative to control. I found the opposite trend for vegetation-dwelling arthropods, which had greater abundances in the control plots relative to the chicken treatments, indicating that the presence of chickens decreases the abundance of vegetation-dwelling arthropods by damaging their habitat or by consuming them, though this needs to be further explored by future studies.
This dissertation will discuss how the loss of biodiversity in farmlands threatens not only ecosystem services provided by wild birds but also threatens the ecological benefits that crop-livestock integration systems may confer to crop production. Preserving and restoring biodiversity through agroecological practices such as by promoting semi-natural habitat to bolster wild bird biodiversity will strengthen farm sustainability. While the consequences of increasing biodiversity through the addition of poultry to a crop rotation system remain vastly understudied, this dissertation suggests that the addition of poultry can have cascading effects on arthropod communities.
Digital Object Identifier (DOI)
This study was supported by the National Science Foundation Graduate Research Fellowship (Grant no.1839289) from 2019-2022.
Garcia, Karina, "NET EFFECTS OF WILD AND MANAGED BIRDS IN AGROECOSYSTEMS" (2022). Theses and Dissertations--Entomology. 64.