Response of host-vector-parasite interactions on forest management systems


Scientific investigators:

Dr. Swen Renner

Willem van Hoesel

(Uni Vienna)

Hypotheses


1. Parasite prevalence in hosts increases with increasing land use intensity.

2. Health effects of parasites on hosts increase with increasing land use intensity because of higher costs of immunoreactions.

3. Land use affects parasite prevalence indirectly through increased vector abundance because of forest structures possibly favoring vector reproduction.

 

Aims

We aim to clarify the relationship between forest habitats and host-vector-parasite interactions. Such effects will be studied within a forest management gradient (i.e., land use intensity) in the Biodiversity Exploratories in order to understand the role of parasitism and vectors for birds and their health status in relation to land use and ecosystem functioning.

We have three specific goals, one for each player in the triad of vectors, parasites, and their hosts:

1. To determine whether blood parasite prevalence and Rickettsia infections of birds depend on land use intensity (forest age classes and structure) at the plot level of the Biodiversity Exploratories for at least six host species representing migrants vs. non-migrants.

2. To determine the health status (immunoreaction) of birds in relation to parasitation and land use intensity (forest structure) in order to understand whether parasites trigger distinct immunoreactions in differently structured forests.

3. To determine the abundance of vectors and parasite prevalence in vectors to assess the probability of infections for birds in relation to forest structure at the plot level of the Biodiversity Exploratories.

The assessment of indirect and variable effects of land use intensity on birds through parasitation is an essential step for understanding whether human land use impacts complex ecological processes and species interactions. We specifically expect to be able to understand whether vectors, and consequently also parasite transmissions, are affected by land use intensity on parasitation processes in bird populations.

 

Methods

  • Capture individuals of Blackcaps (Sylvia atricapilla), European Robin (Erithacus rubecula), European Blackbirds (Turdus merula), Chaffinches (Fringilla coelebs), Great Tits (Parus major), and Blue Tits (Cynistes caeruleus) in 25 forest EPs per Exploratory over the breeding season with repetitions of each plot, draw blood and measure body condition and asymmetries.
  • Determine blood parasites with microscopic and genetic detection methods.
  • Determine the abundance of vectors and their parasitation (infection risk) to assess the probability of infections for birds in relation to forest structure.

 

Summary

The effects of human land use on complex ecological processes and species interactions are poorly understood. Parasitism is an important and complex ecological process; nevertheless, an ecological framework is still missing with regard to the impact of indirect and variable effects of land use intensity on the interaction triad of host-vector-parasites. The assessment of land use effects on birds and their parasitation is an essential step toward understanding whether variable effects of parasites are directly or indirectly explicable by variation in land use intensity. We will measure spatial variability of Haemosporidian infections (parasite prevalence, abundance), host health status (immunoreaction of hosts to infection), and vector abundance (transmission risks to hosts) from local to regional scales and across the Biodiversity Exploratories for six model host species in relation to land use. We specifically expect to be able to understand the role of vectors as a risk factor for parasite transmissions in association with land use intensity on parasitation processes in bird populations.We will capture birds in 75 Experimental Plots representing various levels land use intensity in three Biodiversity Exploratories. We will take blood samples from each bird captured and sample all ticks from the birds. We will determine Haemosporidian parasite prevalence and intensity by counting all blood parasites visible in microscope scans of prepared blood smears and by PCR detection methods. Further, we will determine a standardized infection response (e.g., H/L ratio) and long-term response to costs of immunoreactions of blood-parasites by allocation of resources in the immunoreaction (e.g., asymmetric development of extremities). We will determine dipteran vector abundance through standardized vector capturing on the plots with CO2-baited traps. We will screen the blood meals of the captured vectors for Haemosporidians (PCR) and the sampled ticks for bacterial infections. The infection of vectors should yield an approximation of infection risks for birds in relation to land use. With the data obtained, we will develop a framework concerning the effect of land use intensity on the interaction triad of host-vector-parasites.

 

Previous project contribution of Dr. Swen Renner: Vertebrates