Study
Herbivores and the number of tree species in tropical forests
Janzen, Daniel H.
The American Naturalist, 1970
A model of seed and seedling survival as a function of distance from the parent tree, given that seed predators and pathogens concentrate where seeds are densest, combined with observations of seed predation in tropical forest.
- Studied in
- Angiospermae
- Sample size
- theoretical model with supporting field observation
Seed density falls with distance from the parent while survival probability rises, so recruitment peaks at some distance away rather than beneath the canopy. Where this holds, no species can dominate the area around itself, which leaves space for others.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
Distance- and density-dependent mortality near parent trees is a mechanism maintaining high tree diversity in tropical forests.
How NatureHQ reads it
The single most useful idea for making sense of why dispersal exists at all: the ground under the parent is the most dangerous place a seed can land, and it is dangerous *because* so many siblings are there. Independently proposed by Joseph Connell, which is why it is usually called the Janzen–Connell hypothesis, and it has been supported in many systems and not all.
- Primarily a model; the strength of the effect varies widely between species and forests.
- Temperate systems show it less consistently than tropical ones.
- Distinguishing the predation mechanism from competition among seedlings is difficult in the field.
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Published by: Wiley journalsPublished in a Wiley journal.
This reference was resolved automatically against Crossref on 2026-08-11.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-08-10.