Abstract
As primary producers, plants are known to influence higher trophic interactions by initiating food chains. However, as architects, plants may bypass consumers to directly affect predators with important but underappreciated trophic ramifications. Invasion of western North American grasslands by the perennial forb, spotted knapweed (Centaurea maculosa), has fundamentally altered the architecture of native grassland vegetation. Here, I use long-term monitoring, observational studies, and field experiments to document how changes in vegetation architecture have affected native web spider populations and predation rates. Native spiders that use vegetation as web substrates were collectively 38 times more abundant in C. maculosa-mvadtd grasslands than in uninvaded grasslands. This increase in spider abundance was accompanied by a large shift in web spider community structure, driven primarily by the strong response of Dictyna spiders to C. maculosa invasion. Dictyna densities were 46-74 times higher in C. macw/asa-invaded than native grasslands, a pattern that persisted over 6 years of monitoring. G maculosa also altered Dictyna web building behavior and foraging success. Dictyna webs on G maculosa were 2.94.0 times larger and generated 2.0-2.3 times higher total prey captures than webs on Achillea millefolium, their primary native substrate. Dictyna webs on G maculosa also captured 4.2 times more large prey items, which are crucial for reproduction. As a result, Dictyna were nearly twice as likely to reproduce on G maculosa substrates compared to native substrates. The overall outcome of G maculosa invasion and its transformative effects on vegetation architecture on Dictyna density and web building behavior were to increase Dictyna predation on invertebrate prey >89 fold. These results indicate that invasive plants that change the architecture of native vegetation can substantially impact native food webs via nontraditional plant -► predator -► consumer linkages.
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Claims 8
Claim · model-written summary
Native web spiders were collectively 38 times more abundant in grasslands invaded by spotted knapweed than in uninvaded grasslands.
Verbatim
e0“Native spiders that use vegetation as web substrates were collectively 38 times more abundant in C. maculosa-mvadtd grasslands than in uninvaded grasslands”
Claim · model-written summary
Dictyna spider densities were 46-74 times higher in invaded than in native grasslands, a pattern persisting over 6 years of monitoring.
- Outcome
- Dictyna densitiese0
- Direction
- highere0
- Value
- 46-74 timese0
- Qualifier
- persisted over 6 years of monitoringe1
- Comparator
- native grasslandse0
DictynaOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Dictyna densities were 46-74 times higher in C. macw/asa-invaded than native grasslands”
e1“a pattern that persisted over 6 years of monitoring”
Claim · model-written summary
Dictyna webs on the invasive plant were 2.9-4.0 times larger than webs on the native substrate Achillea millefolium.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Dictyna webs on G maculosa were 2.94.0 times larger and generated 2.0-2.3 times higher total prey captures than webs on Achillea millefolium”
Claim · model-written summary
Dictyna webs on the invasive plant generated 2.0-2.3 times higher total prey captures than webs on Achillea millefolium.
- Outcome
- total prey capturese0
- Direction
- highere0
- Value
- 2.0-2.3 timese0
- Comparator
- webs on Achillea millefoliume0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Dictyna webs on G maculosa were 2.94.0 times larger and generated 2.0-2.3 times higher total prey captures than webs on Achillea millefolium”
Claim · model-written summary
Dictyna webs on the invasive plant captured 4.2 times more large prey items.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Dictyna webs on G maculosa also captured 4.2 times more large prey items”
Claim · model-written summary
Dictyna were nearly twice as likely to reproduce on the invasive plant as on native substrates.
- Outcome
- likely to reproducee0
- Direction
- higherinferrede0
- Value
- nearly twicee0
- Comparator
- native substratese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Dictyna were nearly twice as likely to reproduce on G maculosa substrates compared to native substrates”
Claim · model-written summary
Invasion by the plant and its effects on vegetation architecture increased Dictyna predation on invertebrate prey more than 89-fold.
- Treatment
- G maculosa invasione0
- Outcome
- Dictyna predation on invertebrate preye0
- Direction
- increasee0
- Value
- >89 folde0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The overall outcome of G maculosa invasion and its transformative effects on vegetation architecture on Dictyna density and web building behavior were to increase Dictyna predation on invertebrate prey >89 fold”
Claim · model-written summary
Spider abundance increase was accompanied by a large shift in web spider community structure, driven mainly by Dictyna.
Not reportedDirection
Verbatim
e0“a large shift in web spider community structure, driven primarily by the strong response of Dictyna spiders”