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Oecologia. 2018 Jul;187(3):797-809. doi: 10.1007/s00442-018-4165-8. Epub 2018 May 12.

Defence strategies in African savanna trees.

Author information

1
National Centre for Biological Sciences, Tata Institute of Fundamental Research, GKVK, Bellary Road, Bangalore, 560 065, India. benwigley@gmail.com.
2
School of Natural Resource Management, Nelson Mandela University, George Campus, Madiba Drive, Private Bag X6531, George, 6530, South Africa. benwigley@gmail.com.
3
UMR CNRS 5558, LBBE, Université Claude Bernard Lyon 1, Bât. Grégor Mendel 43 bd du 11 novembre 1918, 69622, Villeurbanne cedex, France.
4
Sustainability Research Unit, Nelson Mandela University, George Campus, Madiba Drive, Private Bag X6531, George, 6530, South Africa.
5
School of Natural Resource Management, Nelson Mandela University, George Campus, Madiba Drive, Private Bag X6531, George, 6530, South Africa.
6
Scientific Services, Kruger National Park, Private Bag X402, Skukuza, 1350, South Africa.

Abstract

Southern African savannas are commonly polarised into two broad types based on plant functional types and defences; infertile savannas dominated by broad-leaved trees typically defended by nitrogen-free secondary compounds and fertile savannas dominated by fine-leaved trees defended by structural defences. In this study, we use trait and other data from 15 wooded savanna sites in Southern Africa and ask if broad-leaved and fine-leaved species dominate on nutrient-poor and nutrient-rich soils, respectively. We then test if there is there any evidence for trade-offs in chemical (i.e., condensed tannins and total polyphenols) vs. structural defences on different soil types. We did not find strong evidence for a general divide in fine- vs. broad-leaved savannas according to soil fertility, nor for a simple trade-off between chemical and structural defences. Instead, we found savanna species to cluster into three broad defence strategies: species were high in leaf N and either (A) highly defended by spines and chemicals or (B) only structurally defended, or (C) low in leaf N and chemically defended. Finally, we tested for differences in browser utilisation between soil types and among plant defence strategies and found that browsing by meso-herbivores was higher on nutrient-rich soils and targeted species from groups A and B and avoided C, while browsing by elephants was mostly not affected by soil type or defence strategy. We propose a framework that can be used as a basis for asking strategic questions that will help improve our understanding of plant defences in savannas.

KEYWORDS:

Broad-leaved; Carbon-based secondary metabolites; Fine-leaved; Mammal browsers; Resource availability; Structural defences

PMID:
29754291
DOI:
10.1007/s00442-018-4165-8

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