Host spatial structure and disperser activity determine mistletoe infection patterns

What processes and factors are responsible for species distribution are
long-standing questions in ecology and a key element for conservation and
management. Mistletoes provide the opportunity to study a forest species
whose occurrence is expected to be constrained by multiple factors as a
consequence of their life form. We studied the mistletoe Tristerix
corymbosus (Loranthaceae) on its most common hosts species in northwest
Patagonia. The seeds of this mistletoe are almost exclusively dispersed by
the small arboreal and endemic marsupial Dromiciops gliroides
(Microbiotheridae). We assessed the underlying causes of plant spatial
patterns through point pattern analysis and we used different variables
that characterize the neighborhood around each host to analyze the
relative effect of host availability, potential for disperser movement,
and canopy light conditions. We found that potential hosts were strongly
aggregated and that the three most common host species were distributed
independent of each other. Considering all host species together, infected
and non-infected host were individually aggregated but segregated from
each other. The aggregated pattern of infected hosts could be explained in
part by the template of potential hosts distribution, but was subsequently
modulated by the activity of the mistletoe disperser. Potential for
disperser movement,  the proximity to reproductive mistletoes and
habitat complexity, increased mistletoe infection probability. However,
neighboring host availability decreased mistletoe infection probability,
and tree DBH (used as surrogate for light conditions) had no detectable
effect. Our results suggested that the distribution of mistletoe infection
was determined by the structure of potential host populations and by the
marsupial disperser activity. Compared to bird dispersed mistletoes, the
scale of the infection was smaller and the proximity to reproductive
mistletoes and habitat complexity were important for seed arrival and
infection. The interplay between landscape structure and disperser
activity determine the spatial structure of mistletoe future generations.