Intensification of livestock production has reduced heterogeneity in vegetative structure in managed grasslands, which has been linked to widespread declines in grassland songbird populations throughout North America. Patch-burn grazing management aims to restore some of that heterogeneity in vegetative structure by burning discrete pasture sections, so that cattle preferentially graze in recently burned areas. Although patch-burn grazing can increase reproductive success of grassland songbirds, we know little about possible interactions with regional variation in predator communities or brood parasite abundance, or annual variation in weather conditions. Using six years of data from two tallgrass prairie sites in eastern Kansas, USA, we tested effects of patch-burn grazing on the rates of brood parasitism, clutch size, nest survival, and fledging success of three common grassland songbirds, Dickcissels (Spiza americana), Eastern Meadowlarks (Sturnella magna), and Grasshopper Sparrows (Ammodramus savannarum), among pastures managed with patch-burn grazing versus pastures that were annually burned and either grazed or ungrazed. Dickcissel nests experienced lower parasitism (72.8 ± 4.6% SE vs. 89.1 ± 2.2%) and Eastern Meadowlarks had higher nest survival (63.2 ± 20.5% vs. 16.5 ± 3.5%) in annually burned and ungrazed pastures than pastures managed with patch-burn grazing. However, average number of host fledglings per nesting attempt did not differ among management treatments for any species. Annual variation in weather conditions had a large effect on vegetation structure, but not on reproductive success. Probability of brood parasitism was consistently high (25.5‒84.7%) and nest survival was consistently low (9.9–16.9%) for all species pooled across treatments, sites, and years, indicating that combined effects of predation, parasitism and drought can offset potential benefits of patch-burn grazing management previously found in tallgrass prairies. Although differences in reproductive success among management treatments were minimal, patch-burn grazing management could still benefit population dynamics of grassland songbirds in areas where nest predators and brood parasites are locally abundant by providing suitable nesting habitat for bird species that require greater amounts of vegetation cover and litter, generally not present in burned pastures.
This content will become publicly available on August 15, 2024
Co‐parasitism is ubiquitous and has important consequences for the ecology and evolution of wild host populations. Studies of parasite co‐infections remain limited in scope, with few experimental tests of the fitness consequences of multiple parasites, especially in natural populations. We measured the separate and combined effects of Using a two‐factor experimental approach, we manipulated the presence of nest flies and cowbirds in mockingbird nests and assessed their effects on mockingbird haemoglobin levels, begging and provisioning rates, body size, and fledging success. We also monitored rates of nest predation in relation to parasitism by flies and cowbirds. Nest flies reduced the haemoglobin concentration, body size, and fledging success of mockingbirds, likely because mockingbirds did not compensate for parasitism by begging more or feeding their nestlings more. Cowbirds also reduced the fledging success of mockingbirds, even though they had no detectable effect on haemoglobin or body size. Nests with cowbirds, which beg more than mockingbirds, attracted more nest predators. There was no significant interaction between the effects of flies and cowbirds on any component of mockingbird fitness. The combined effects of nest flies and cowbirds were strictly additive. In summary, we show that nest flies and cowbirds both reduce host fitness, but do not have interactive effects in co‐parasitized nests. Our results further suggest that predators exacerbate the effects of nest flies and cowbirds on their hosts. Our study shows that the fitness consequences of co‐parasitism are complex, especially in the context of community‐level interactions.
- Award ID(s):
- 2025085
- NSF-PAR ID:
- 10443058
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Animal Ecology
- ISSN:
- 0021-8790
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract Nest‐sharer avian brood parasites do not evict or otherwise kill host chicks, but instead inflict a range of negative effects on their nestmates that are mediated by interactions between the parasite and host life history traits. Although many of the negative fitness effects of avian brood parasitism are well documented across diverse host species, there remains a paucity of studies that have examined the impacts of parasitism across the entirety of host ontogeny (i.e., from when an egg is laid until independence). More specifically, few studies have examined the impact of brood parasitism on the pre‐ and post‐fledging development, physiology, behavior, and survival of host offspring. To help fill this knowledge gap, we assessed the effects of brood parasitism by Brown‐headed Cowbirds (
Molothrus ater ) across the ontogeny (incubation, nestling, and post‐fledging period) of nine sympatrically breeding host species in central Illinois, USA; due to sample sizes, impacts on the post‐fledging period were only examined in two of the nine species. Specifically, we examined the impact of brood parasitism on ontogenetic markers including the embryonic heart rate, hatching rate, nestling period length, nest survival, and offspring growth and development. Additionally, in species in which we found negative impacts of cowbird parasitism on host nestmate ontogeny, we examined whether the difference in adult size between parasites and their hosts and their hatching asynchrony positively predicted variation in host costs across these focal taxa. We found that costs of cowbird parasitism were most severe during early nesting stages (reduction in the host clutch or brood size) and were predicted negatively by host size and positively by incubation length. In contrast, we only found limited costs of cowbird parasitism on other stages of host ontogeny; critically, post‐fledging survival did not differ between host offspring that fledged alongside cowbirds and those that did not. Our findings (i) highlight the direct costs of cowbird parasitism on host fitness, (ii) provide evidence for when (the stage) those costs are manifested, and (iii) may help to explain why many anti‐cowbird defenses of hosts have evolved for protection from parasitism during the laying and incubation stages. -
more » « less
Abstract Human activity changes multiple factors in the environment, which can have positive or negative synergistic effects on organisms. However, few studies have explored the causal effects of multiple anthropogenic factors, such as urbanization and invasive species, on animals and the mechanisms that mediate these interactions. This study examines the influence of urbanization on the detrimental effect of invasive avian vampire flies (
Philornis downsi ) on endemic Darwin's finches in the Galápagos Islands. We experimentally manipulated nest fly abundance in urban and non‐urban locations and then characterized nestling health, fledging success, diet, and gene expression patterns related to host defense. Fledging success of non‐parasitized nestlings from urban (79%) and non‐urban (75%) nests did not differ significantly. However, parasitized, non‐urban nestlings lost more blood, and fewer nestlings survived (8%) compared to urban nestlings (50%). Stable isotopic values (δ15N) from urban nestling feces were higher than those from non‐urban nestlings, suggesting that urban nestlings are consuming more protein. δ15N values correlated negatively with parasite abundance, which suggests that diet might influence host defenses (e.g., tolerance and resistance). Parasitized, urban nestlings differentially expressed genes within pathways associated with red blood cell production (tolerance) and pro‐inflammatory response (innate immunological resistance), compared to parasitized, non‐urban nestlings. In contrast, parasitized non‐urban nestlings differentially expressed genes within pathways associated with immunoglobulin production (adaptive immunological resistance). Our results suggest that urban nestlings are investing more in pro‐inflammatory responses to resist parasites but also recovering more blood cells to tolerate blood loss. Although non‐urban nestlings are mounting an adaptive immune response, it is likely a last effort by the immune system rather than an effective defense against avian vampire flies since few nestlings survived. -
more » « less
Abstract The phenotypic expression and fitness consequences of behaviours that are exhibited during social interactions are especially sensitive to their local social context. This context‐dependence is expected to generate more variation in the sign and magnitude of selection on social behaviour than that experienced by static characters like morphology. Relatively few studies, however, have examined selection on behavioural traits in multiple populations.
We estimated sexual selection in the wild to determine if the strength and form of selection on social phenotypes is more variable than that on morphology.
We compared selection gradients on social network position, body size, and weaponry of male forked fungus beetles
Bolitotherus cornutus as they influenced mating success across nine natural subpopulations.Male horn length consistently experienced positive sexual selection. However, the sign and magnitude of selection on individual measures of network centrality (strength and betweenness) differed significantly among subpopulations. Moreover, selection on social behaviours occurred at a local scale (‘soft selection’), whereas selection on horn length occurred at the metapopulation scale (‘hard selection’).
These results indicate that an individual with a given social phenotype could experience different fitness consequences depending on the network it occupies. While individuals seem to be unable to escape the fitness effects of their morphology, they may have the potential to mediate the pressures of selection on behavioural phenotypes by moving among subpopulations or altering social connections within a network.
-
more » « less
Abstract Investment in defence may not be uniformly beneficial across an organism's lifespan. Risk, and therefore potential payoff of defence, may change with age and behaviour, but for colony‐living organisms, it may also change with colony size and reproductive stage.
The acorn ant
Temnothorax longispinosus uses venom to defend against socially parasitic ants that raid their nests to steal brood. We investigated the idea thatT. longispinosus adjust their venom allocation in accordance with raid risk. We tested the predictions thatT. longispinosus ants should produce more venom when raids are most likely to occur and during the parts of the nest reproductive cycle when the potential fitness loss per raid is highest. We also asked whether venom volume varies between nurses and foragers within a colony, which have different potential risk levels, and whether this difference increases with colony size.We found that workers had more venom in the summer, both before and during the period when raids occur, than in the fall when pupae were no longer present in nests. Workers engaging in nursing behaviours had more venom as the pupa to worker ratio in the nest increased, indicating that nurses invest more in venom as the relative number of pupae requiring defence increases. In addition, the difference in venom volume between nurses and foragers grew with colony size.
These results provide observational support for the hypothesis that individuals vary their investment in venom over their colony's development in conjunction with the risk of social parasitism.
