In this thesis, I investigate the presence of reverse Janzen-Connell effects in
ant-plant communities in Papua New Guinea. Janzen-Connell effects help to
explain species diversity maintenance by focusing on natural enemies' role in
controlling plant distributions. It is postulated that spillover of enemies near
adult plants reduces seedling survival, promoting coexistence and diversity.
Conversely, reverse Janzen-Connell effects occur when mutualists enhance
survival near conspecific adults, potentially creating larger recruitment zones
leading in the extreme to species monodominance. I use a combination of
observation and ant exclusion experiments, as well as spatial analysis to
explore reverse Janzen-Connell effects. Ant-plant interactions, particularly
myrmecophytic ones, show moderate species specificity, a key assumption of
classic Janzen-Connell effects. Mutualistic ants enhance plant viability by
eliminating herbivores and pathogens, reducing damage, and optimizing
photosynthesis. I also explore the specificity of myrmecophytic systems
compared to other ant-plant interactions across environments using a data
collation approach. I speculate that reverse Janzen-Connell effects can be
observed in ant-plant mutualisms, ectomycorrhizal fungi, and plants. I also
found through a global meta-analysis that myrmecophytic networks are the
most specialized, with specialisation being driven by network type rather than
environmental factors. Thus, myrmecophytes are a suitable system to explore
the presence of reverse Janzen-Connell effects. Spatial analysis showed the
presence of reverse Janzen-Connell effects in plants in seedlings of Meliaceae
family and less strongly in adults. In the ant exclusion experiments,
conspecific saplings exhibited higher survival and growth, but this was not
related to the treatment itself meaning the plants are potentially benefiting
from root fungi from adult conspecifics. Saplings with ant patrolling had better
survival, although caution is needed due to small sample size. Lastly, I found
that ant inhabitation positively influenced growth in older ant-plants, but this
was not linked to local ant-plant density, and leaf loss from herbivory was
lower when saplings were near adult conspecifics, possibly due to protective
volatiles. Taken together this suggests some weak evidence for reverse JanzenConnell effects in the lowland rainforest of Papua New Guinea.
In this thesis, I investigate the presence of reverse Janzen-Connell effects in
ant-plant communities in Papua New Guinea. Janzen-Connell effects help to
explain species diversity maintenance by focusing on natural enemies' role in
controlling plant distributions. It is postulated that spillover of enemies near
adult plants reduces seedling survival, promoting coexistence and diversity.
Conversely, reverse Janzen-Connell effects occur when mutualists enhance
survival near conspecific adults, potentially creating larger recruitment zones
leading in the extreme to species monodominance. I use a combination of
observation and ant exclusion experiments, as well as spatial analysis to
explore reverse Janzen-Connell effects. Ant-plant interactions, particularly
myrmecophytic ones, show moderate species specificity, a key assumption of
classic Janzen-Connell effects. Mutualistic ants enhance plant viability by
eliminating herbivores and pathogens, reducing damage, and optimizing
photosynthesis. I also explore the specificity of myrmecophytic systems
compared to other ant-plant interactions across environments using a data
collation approach. I speculate that reverse Janzen-Connell effects can be
observed in ant-plant mutualisms, ectomycorrhizal fungi, and plants. I also
found through a global meta-analysis that myrmecophytic networks are the
most specialized, with specialisation being driven by network type rather than
environmental factors. Thus, myrmecophytes are a suitable system to explore
the presence of reverse Janzen-Connell effects. Spatial analysis showed the
presence of reverse Janzen-Connell effects in plants in seedlings of Meliaceae
family and less strongly in adults. In the ant exclusion experiments,
conspecific saplings exhibited higher survival and growth, but this was not
related to the treatment itself meaning the plants are potentially benefiting
from root fungi from adult conspecifics. Saplings with ant patrolling had better
survival, although caution is needed due to small sample size. Lastly, I found
that ant inhabitation positively influenced growth in older ant-plants, but this
was not linked to local ant-plant density, and leaf loss from herbivory was
lower when saplings were near adult conspecifics, possibly due to protective
volatiles. Taken together this suggests some weak evidence for reverse JanzenConnell effects in the lowland rainforest of Papua New Guinea.
Present all members of committee: Oldřich Nedvěd, Eva Kaštovská, Jana Jersáková, Alena Bartoňová, Kateřina Sam, reviewers Sofia Grippenberg and Pavel Drozd.
Supervisor Tom Fayle introduced S.Z. Presentation 14.08-14-35. Specific comments by T.F. Review and questions of S.G.: enthusiastic reading, substantial contribution to research; throughout understanding the system; Q&A: mechanism of RJC not affected by elevation and latitude, but myrmecophytic plants not in high latitude; density effect: different age cohort surrounding the old tree; low proportion of plants with ants due to abiotic factors; monodominant stands rare in tropics, when it happens, it is severe; invasive plants get natural enemies and root mycorhiza;
P.D: (14:59) mixture of review, metaanalysis and experiment; Q&A: in which habitats it can occur in temperate zone? - by large herbivores, by mycorhyzis, not by ants; ant hills have higher diversity of seedlings; lmer and AIC in metaanalysis (regression); prisme protocol - was required in one journal for metaanalysis; application in agriculture? - less density, two crops together, genetic diversity of one crop, sharing predators;
E.K.: ectomycorhyzis is specific? - for family; J.J.: specialist x generalists - different plant view and ant view; pollinators more specific in temperate? - says literature, less specific in tropics , no other option; positive and negative JCE can cancel each other? - difficult experiment; A.S.: how + and - effects can be made by fungi? - combination of pathogens and mutualists; K.S.: JCE not working because volatiles? - emitted to several meters; fungi and volatiles? - larger growth with mycorhyzis.