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Epiphyte Ecology
Monitoring Change
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Dr Brian Coppins
Ms Sally Eaton
Dr Christopher Ellis
Ms Louise Olley
Dr Rebecca Yahr

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Introduction

Mechanistic models are increasingly important in RBGE's epiphyte research, and are used in three ways:

(i) in order to validate Bioclimatic Models, by demonstrating that distributions have a functional basis through association with a species' ecological fitness measured experimentally [1],

(ii) to understand how species distributions in the present-day landscape might be affected by real-world ecological processes such as habitat connectivity (metapopulation dynamics), habitat quality, patch dynamics, ecological fitness (species growth rates) and fecundity,

(iii) to frame these ecological processes within a climate change context [2], by understanding how climate change might affect factors such as the species use of different microhabitats (habitat quality), or species growth rates, in the context of habitat management.

Population Dynamics and Species Distributions

Our research has confirmed an extinction debt for lichen epiphytes, in which species richness is higher than expected for woodland stands, given the present-day extent/connectivity of habitat [3, 4]. This suggests that the populations of certain epiphytes may continue to be lost from woodland stands over a period of centuries, unless habitat is sufficiently regenerated into the landscape.

However, we are now developing population models for epiphytes, which link internal dynamics (microhabitat quality or carrying capacity, microhabitat patch turnover or mortality rates, growth rates and generation times, and fecundity) with inter-patch dispersal (metapopulation dynamics).

Preliminary results confirm - for biologically plausible values - the slow decline to population extinction for isolated populations in fragmented habitat (extinction debt). These results also suggest that regeneration of woodland habitat may be insufficient to recover epiphyte populations given the historical pattern of woodland loss in Scotland. This strongly implies that species Translocation may now be necessary for epiphyte conservation.

Habitat Management and Climate Change

Our previous work has demonstrated that lichen epiphytes show contrasting habitat specificity along climatic gradients. This is demonstrated for 'oceanic' old growth indicator species, which are preferentially associated with ancient woodland in sub-optimal climates, but have more generalist woodland associations in optimal climates [5].

We are now applying our population dynamic models (see above), to understand what controls these shifts in habitat specificity, and in particular the role of changing microhabitat suitability/availability, and/or changing values for growth rates, generation times and fecundity.

Experiments on lichen physiology and growth rates are being expanded to improve the accuracy of population models, through the use of common garden growth experiments at three botanic garden sites (Figure 1). These experiments have additional aims of (i) understanding how microhabitats can be managed into a woodland to offset the negative effect of macroclimatic change, and (ii) understanding how ecological fitness may be affected by non-analogue climates.

Figure 1. Lichen growth frame and experimental pendants for multiple species at three climatically-contrasting botanic garden sites.

References:

[1] Eaton, S. & Ellis, C.J. (2012) Local experimental growth rates respond to macroclimate for the lichen epiphyte Lobaria pulmonaria. Plant Ecology and Diversity, 5: 365-372.

[2] Ellis, C.J. & Coppins, B.J. (2007) Changing climate and historic-woodland structure interact to control species diversity of the 'Lobarion' epiphyte community in Scotland. Journal of Vegetation Science, 18: 725-734.

[3] Ellis, C.J. & Coppins, B.J. (2007) 19th Century woodland structure controls stand-scale epiphyte diversity in present-day Scotland. Diversity & Distributions, 13: 84-91.

[4] Ellis, C.J. & Coppins, B.J. (2009) Quantifying the role of multiple landscape-scale drivers controlling epiphyte composition and richness in a conservation priority habitat (juniper scrub). Biological Conservation, 142: 1291-1301.

[5] Ellis, C.J., Yahr, R. & Coppins, B.J. (2009) Local extent of old-growth woodland modifies epiphyte response to climate change. Journal of Biogeography, 36: 302-313.