Luke Mander - Projects

The Geological History of Tropical Rainforests

Tropical rainforests are the most structurally complex and diverse land ecosystems on Earth. The fossil record of leaves indicates that they have a history stretching at least to the Paleocene (~58 million years ago) (Wing et al. 2009; PNAS, 106:18627–18632), and the fossil record of pollen and spores has been used to show that Neotropical plant diversity is sensitive to global temperature (Jaramillo et al. 2006; Science, 311, 1893–1896), and that the end-Cretaceous mass extinction event reduced Neotropical plant diversity by 45% (Carvalho et al. 2021; Science, 372, 63–68).

At present there is a lack of fossil data on the evolutionary history of rainforests in the Old World tropics, particularly in West Africa. In order to address this gap I am working with collaborators to undertake primary descriptive taxonomic work on fossil pollen and spores from Nigeria, and palaeoecological work on the diversity and composition of fossil assemblages in order to understand the geological history of rainforests in this region. Our work so far has focussed on the Paleocene–Eocene of the northern Niger Delta, and has resulted in the redescription of existing taxa (see figure to the right), and the description of new genera and species. Such taxonomic work provides the foundation for reconstructing plant biodiversity in the geological past, and will facilitate studies of the biogeographical evolution of rainforests using plant fossils.

Saturna enigmaticus Salard-Cheboldaeff 1978 is a beautiful and intriguing pollen grain from the Paleocene–Eocene of Nigeria (Mander L., Jaramillo C. & Oboh-Ikuenobe F.E. 2023. Descriptive systematics of Upper Paleocene–Lower Eocene pollen and spores from the northern Niger Delta, southeastern Nigeria. Palynology, 2200525.)

Figure from: Mander L., Parins-Fukuchi, C., Dick, C.W., Punyasena S.W. & Jaramillo C. (2020) Phylogenetic and ecological correlates of pollen morphological diversity in a Neotropical rainforest. Biotropica, 53, 74–85.

Pollination Biology in Tropical Rainforests

The transfer of pollen grains from male to female reproductive apparatus is a critical part of plant reproduction that produces seeds and a new generation. The process of pollination ultimately sustains plant populations, and the interactions between plants and their pollinators represent complex interaction networks that have been called the architecture of biodiversity (Bascompte & Jordano 2007; Annual Review of Ecology Evolution and Systematics, 38, 567–593).

However, very little is known about pollination in tropical rainforests. Partly this reflects a lack of research on the topic, but also reflects the difficulty of obtaining data on plants that flower infrequently and have flowers that are largely inaccessible in the canopy. We are focussing our efforts on the flora of Barro Colorado Island, Panama, and our results so far have shown that the pollen grains of biotically pollinated plants are more morphologically diverse than those of abiotically pollinated plants (see figure to the left). This provides a potential link between pollination ecology and pollen morphology that we are currently investigating further.

Leaf Venation and the Evolution of Complex Networks

Networks vary widely in their architecture and functional properties. Modelling work has shown that networks optimized for transportation efficiency are branching trees, while networks optimized for resistance to damage and fluctuating flow are characterized by loops. These two architectures are found in leaf venation networks, and among living plants examples of branching networks are found in ferns as well as the seed plant Ginkgo, while networks with loops are typical of flowering plants and some ferns.

The evolutionary transition from branched to reticulate leaf venation networks occurred in the Carboniferous around 320 million years ago, and together with collaborators I am undertaking anatomical and computational analyses of venation networks in living and fossil leaves to measure key morphological variables such as leaf shape and the degree of connectivity between anastomosing veins, and quantify the performance of real-world network architectures under damage (see figure to the right). Ultimately this work aims to shed light on how and why complex networks evolve in nature.

Simulated herbivory on the Carboniferous leaf Linopteris subbrongniartii.