Density-dependent decline of host abundance resulting from a new infectious disease

Abstract

Month by month we tracked the spread of the epizootic of an apparently novel strain of a widespread poultry pathogen, Mycoplasma gallisepticum, through a previously unknown host, the house finch, whose abundance has been monitored over past decades. Here we are able to demonstrate a causal relationship between high disease prevalence and declining house finch abundance throughout the eastern half of North America because the epizootic reached different parts of the house finch range at different times. Three years after the epizootic arrived, house finch abundance stabilized at similar levels, although house finch abundance had been high and stable in some areas but low and rapidly increasing in others. This result, not previously documented in wild populations, is as expected from theory if transmission of the disease was density dependent.

Host Range and Dynamics of Mycoplasmal Conjunctivitis Among Birds in North America

“…We indirectly controlled for changes in the population dynamics and range of each species by incorporating data from PFW. For example, house finch populations have declined throughout much of eastern North America after the emergence of mycoplasmal conjunctivitis (Hochachka and Dhondt, 2000), and the purple finch is noted for quasicyclical irruptions across its winter range that likely impact its contact with house finches and exposure to pathogenic organisms. Bird feeding activity by the general public, however, was assumed to be unchanged throughout the survey period though this may represent a significant risk factor for the transmission of conjunctivitis in songbirds (Hartup et al, 1998).…”

An appetite for connection: why we need to understand the effect and value of feeding wild birds

“…The best known of these was the conjunctivitis epidemic among American House Finches (Carpodacus mexicanus) in the eastern USA, a phenomenon initially reported among birds visiting feeders (Dhondt et al 2001). The subsequent monitoring of the spread of the disease was achieved by recruiting large numbers of feeder operators in one of the most effective examples of large-scale 'citizen science' (Hochachka and Dhondt 2000). This army of motivated participants enabled researchers to follow the outbreak through its peak c. 2004 (when~15% of the eastern population of House Finches were infected) and the later 'plateau' phase (Cornell Lab Remarkably similar characteristics surround the discovery and monitoring of the protozoan disease Trichomoniasis gallinae in the UK, which was declared an epidemic in 2005 (Robinson et al 2010).…”

Invasions of non-native earthworms related to population declines of ground-nesting songbirds across a regional extent in northern hardwood forests of North America

“…Elucidating the impacts of invasives to populations and ecosystems requires local-scale research to be complemented by regional and continental-scale investigations (Crowl et al 2008). Whereas the spread of invasive diseases has been linked to regional and continental population declines of North American birds (Hochachka and Dhondt 2000;LaDeau et al 2007), incomplete information about distributions of many invasives has limited most research of effects on birds to relatively small spatial scales (e.g. study areas \100,000 ha).…”