Lea van de Graaf from the University of Leiden, Netherlands and Carolina Madeira from the University of Lisbon, Portugal have recently published an account of rich invertebrate communities in tropical epiphytes. Their study involved sampling 18 elephant ear ferns (Platycerium elephantotis) in Kibale National Park, Uganda to investigate the macroinvertebrate populations on, and within, suspended soil.

The objectives of this study were:

1. to survey the biodiversity and species richness, as well as organisms’ density within these ferns
   
2. to compare macroinvertebrate communities from ferns at different heights and of different weights
   
3. identify patterns of macroinvertebrate assemblages according to the mentioned variables
   

Individual ferns on 18 randomly-selected trees were removed and thoroughly dissected to collect all fauna within. 

They speculate that this epiphyte may be a nursery for macroinvertebrates because they found high numbers of caterpillars, cocoons, pupas and eggs in their samples.

When addressing their second objective they found that there were no significant relationships between invertebrate diversity or abundance and height or weight of the epiphyte. The authors speculate that the diversity and abundance of invertebrates is more likely related to the microhabitat within each fern and suggest that the presence or absence of canopy soil is probably an important factor in determining critter populations.

The authors conclude that invertebrate populations within epiphytes are an overlooked but important component of forest diversity. They state that: 

"There will undoubtedly be other, overlooked, concentrations of invertebrates in the canopy, living in a wide range of habitats other than epiphytes. As further studies are made of the animals both in epiphytes and elsewhere in the canopy, the estimates of total invertebrate biomass will increase and the relative importance of epiphytes may need to be revised."

This conclusion is very similar to that from our recent epiphyte fauna study in NZ, which is: we need to study our forest canopies more!

A new article about facilitation cascades has been published by Christine Angelini and Brian Silliman from the University of Florida. It is such an interesting contribution to our understanding of epiphyte ecology that I'm going to dedicate four blogs to it. This week: a model to explain the application.

To understand and predict species assemblages and interactions in different facilitation cascades we can use the Foundation Species-Biodiversity model: 

According to this model, facilitation cascades can be described using three categories based on the difference that secondary foundation species make to the community:

Type A: 
Secondary foundation species support more individuals of species that are already in the community (increased abundance) by providing functional traits that are similar to those of the foundation species.

Type B: 
Secondary foundation species provide habitat for different individuals (increased diversity) by providing different functional traits than the foundation species.

Type C: 
Secondary foundation species support more individuals of the existing species AND individuals of new species (increased abundance AND diversity) through the provision of a range of traits. 

Notes: some secondary species may not significantly increase either abundance or diversity, and facilitation cascades can switch if environmental conditions change.

Examples of each facilitation cascade. Simplified from Angelini & Silliman:

Type A: 

Foundation species: shoal grass
Secondary foundation species: manatee grass

Manatee grass facilitates an increase in the abundance of resident invertebrates and fish by providing more habitat of a similar nature. In other words, more of the same services.

Type B:

Foundation species: turtle grass
Secondary foundation species: pen shells

Pen shells facilitate increased diversity by providing places for fish to lay eggs. In other words, new and different services.

Type C:

Foundation species: mangroves
Secondary foundation species: oysters

Oysters facilitate both an increase in diversity and abundance. They provide more habitat for species that already inhabit mangrove roots but also provide habitat for species that are oyster-dependant.

Next week: application of all of this theory to New Zealand epiphytes!

An exciting new article about facilitation cascades has been published by Christine Angelini and Brian Silliman from the University of Florida. It is such an interesting contribution to our understanding of epiphyte ecology that I'm going to dedicate four blogs to it. This week: an epiphyte study.

Angelini & Silliman (In Press) conducted a range of experiments in Southern USA to investigate the relationships between Southern live oak trees (Quercus virginiana) and Spanish moss (Tillandsia usneiodes) a common epiphyte that is infact in the bromeliad, not moss, family. I'll briefly run through some of the interesting things that they discovered.

Oak-Tillandisa-insect facilitation cascade:

• Oak trees are a foundation species that provide habitat for Tillandsia 
• Tillandsia is a secondary foundation species that provides habitat for a diverse and abundant community of invertebrates
  

Key evidence:
Tillandsia relies on oak trees to provide conditions that it can establish and survive in. In this part of the world the conditions on the ground are hot and dry and very unfavourable for Tillandsia.

Within an oak tree, clumps of Tillandsia (called festoons) increase the structure, or physical space, available for insect habitat as well as stabilising temperature and humidity. This increases not only the abundance of invertebrates already present in the tree, but also in the number of species, the different types of feeding guilds (e.g. decomposers, herbivores), and the life stages (e.g. juveniles, adults). These invertebrates cannot survive on the tree without the epiphytic Tillandsia.

One example of the Tillandsia providing for invertebrates also happens to be my favourite part of this study: 
The researchers found that Tillandsia acts as a nursery by protecting juvenile crickets from spider predation. This experiment involved releasing baby crickets onto A) a branch with no epiphytes and B) a branch with Tillandsia, then letting the spiders loose! After 12 hours they counted live crickets and inspected dead crickets to find that the branch with Tillandsia had a 95 % cricket survival rate while the bare branch had only 60 % and all dead crickets had spider wounds... can't argue with that!

Next week: a model to understand the roles that different species play in facilitation cascades.

The epiphytic flora of New Zealand has interesting similarities with the epiphytes of tropical rainforests. For example, we have diverse epiphytic species that belong to many different plant groups: ferns, orchids, shrubs etc. However, these groups of plants also have stark differences and today's example is the cacti!  

Forget what comes to mind when you imagine a cactus because the cacti of tropical Americas do not grow in sand nor do they have large spikes. Species such as those belonging to Rhipsalis grow as epiphytes and have long leaves without any spikes. They also have tiny flowers and  fruit that emerge from the leaves.

Species of Rhipsalis are thought to have specialist relationships with one group of tropical birds. A recent study by Guaraldo and colleagues compared the requirements for Rhipsalis seed germination to that of mistletoes; a plant group that is considered to rely on specialist dispersers. Both of these plant groups have sticky seeds that are most successful if they are stuck in the fork of a large branch with suitable bark. Species of Rhipsalis are even known as "mistletoe cactus" because the fruit are so similar. Interestingly, the seeds of Rhipsalis and mistletoe species are both primarily distributed by Euphonia birds. These birds do a good job of establishing sticky seeds because they smear the seeds onto a host branch rather than dropping them, providing a much better chance for establishment. 

New Zealand's epiphytic flora does not have any cacti species, nor any known specialist bird relationships. We do know that some mistletoe species rely on tui and bellbirds for pollination and that the woody vine kiekie might have had a relationship with bats in the past (before they were lost from many areas) but these plants aren't epiphytes - maybe epiphytes like the Pittosporum shrubs species have (or had) important relationships with fauna, it is after all still unclear how their seeds are dispersed. Is anyone out there looking for a research topic?!