Comunidad Una comunidad es, de acuerdo con Tonnies (1887) citado por Posada (1998 1999)

Identifying a narrow set of measures for biodiversity is preferable for the reasons described in Section 2.2. We must escape the “curse of bioinformatics”, the uncoordinated proliferation of

biodiversity measures, to have a shared global measure of biodiversity (Faith and Baker 2006). But we should be conciliatory. We want a measure which correlates with the diversity of features measured in other descriptions of biodiversity. Measures of phylogenetic diversity have often been defended primarily due to their representativeness. Regions or species which are described as biodiverse under other measures tend to also appear biodiverse under phylogenetic measures. This idea is at the core of Faith’s defence of phylogenetic diversity (Faith 1992). He argues that we can use

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the branch lengths of phylogenies to represent the change in biological features and the functional attributes of populations. Branch length is thought to be representative of “feature diversity”, which is not a property of individual organisms, like different gene sequences, but of whole populations, like evolutionary plasticity. By finding the record of historical change in populations, we can represent the change in biological features of populations. This is the reason commonly given in the biological literature for using phylogenetic measures to represent diversity and has empirical support (Forest et al. 2007; Huang et al. 2012).

The representativeness of phylogenetic diversity is debated within the biodiversity literature. Winter et al. (2013) argue that the relationship between functional features and phylogenetic diversity is variable so we should not use phylogenetic diversity without reservations (also see Devictor et al. 2010). Other researchers have investigated the conditions that cause this relationship to diverge, such as competition driving functional differentiation in closely related species or slow trait evolution causing a population’s functional differentiation to be limited (Safi et al. 2011). The relationship between phylogenetic diversity and general trait diversity, while contested, is supported but still open to the weight of further empirical evidence.

In reply to sceptics of phylogenetic diversity’s representation of functional diversity, I believe they understate the variation in functional diversity measures, given a character set. Varying the characters included in a functional measure will result in different populations being functionally diverse. It is not possible to provide a global tractable set of characters for measuring functional diversity. This due to the radical difference in the morphology of the different clades of life. It is near impossible to have a functional measure that can assess the relative functional uniqueness of a Scribbly Gum and a Scribbly Gum Moth. Without a shared functional measure across life, we cannot anchor our judgements about the relationship of function to phylogenetics on a global scale.

Consider the diversity of function diversity methodologies. To measure functional diversity scientists must make a series of decisions as to what sort of feature in the world they want to measure and the units they want to use to measure this feature. In functional diversity, the phenomena they may aim to describe can include resource cycling, or traits that maintain populations, or

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morphological differences between populations. The biological phenomena these measures aim to describe will be fundamentally different, encompassing what a population does or an organism’s anatomy or the behaviour of a population. We can ask about how any or all of these carvings of functional diversity relate to phylogenetics; some may co-vary more closely than others, but each will be a different question. Given this challenge, it is unsurprising that functional diversity does not always exactly track phylogenetic diversity.

Even when we reduce our scope to just consider variation in morphology or anatomy, there is no clear or principled set of traits shared across life in the way that phylogeny is (as argued in

tractability). We cannot compare the morphology of dorsal fins with antennae. The lack of principled theoretical grounding in what biological features are measured in functional diversity is exemplified by the practice of demarcating characters to do function measures. Many biologists decide what biological features to measure through convention, diversity of functional characters in organisms is what scientists perceive as important.

It should then be expected that there are variable relationships between functional diversity and phylogenetic diversity, particularly as there will be extremely variable relationships between one measure of functional diversity and another. If we wished to force a relationship between these measures, we could systemically go through each measure and consider how the pair of functional diversity and phylogenetic diversity measures co-vary. With likely thousands of combinations some pairs of measures with co-vary strongly and some will not. This is, however, a hollow way to do research. Both measures of functional and phylogenetic diversity are independently valuable (more on the independent value of phylogeny in theoretical fundamentality). Phylogenetic diversity is better as a global measure of diversity due to the universality of its character set. Function diversity is valuable when it is local and goal oriented. It is best used when variation in a functional trait is known to do something in an ecosystem. This constrains what should be measured.

These measures are not completely unrelated, phylogenetic measures can aid in categorising functional and morphological character sets. Very few traits are shared throughout life. The evolution of an elephant and an ant involve very different biological mechanisms and traits. These different

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mechanisms and traits are, however, common to a local clade structure. The evolution of wings and chitin exoskeletons are relevant to the clade that ants (Formicidae) belong to but not particularly relevant to elephant evolution28_{. The relevant morphological features can be categorized through} homology. These are structures, which are modified through selection on variation in developmental processes. By placing traits or mechanisms within their lineage structure, we provide a context for analysing these features in reference to their closest relatives. Phylogenetics not only correlates with other categorizations of biological difference but also provides a context that allows for their meaningful differentiation. The clade therefore provides a reference class for the description of morphological traits. This allows for what Maclaurin and Sterelny (2008) call a “local morphospace”, a limited set of morphological features which vary within a clade. These functional measures in many contexts can be used in many contexts to further supplement phylogenetic measures of diversity.

Equating biodiversity with phylogenetic structure ties biodiversity to biological relations which exist on a global scale. Global phylogenetic diversity can be used to identify key endemic taxa that represent distinct clades with long branches and few extant species. This is already being used by groups such as EDGE (Evolutionary Distinct and Globally Endangered) of Existence program operating out of the Zoological Society of London29_{. From initial global priorities we can move into} finer scale, selecting between populations that equally represent clades. Considerations on the finer scale turn on choices of whether to preserve more individual lineages or preserving fewer but more representative lineages. Choices will likely be influenced by features internal to clades including biological features that are not based in phylogenies, which also contribute to biodiversity. These features could be biological, such as how plastic or morphologically diverse the clade is, or ecological like the local causal context of the population, particularly what other populations they causally influence. For example, a species with a significantly larger body size to its related sister species will be functionally unique, which gives us a reason to prefer them their nearby relatives.

28 _{Even natural selection itself may differ between these lineages if the ants are colony forming (see} Godfrey-Smith 2009; Haber 2013).

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Identifying a measure which is representative over both global and local scales is critical as it has been discovered that local measures of diversity can appear to contradict global measures. Across the world, local species richness has been steadily increasing according to several meta-analyses (Vellend 2017). This finding is due to invasive species spreading across the globe, increasing the local species count. This process is coupled with species local to these regions becoming extinct, leading to global species diversity being lost. So, many habitats on earth are increasing the alpha diversity, the count of units of diversity in an area, usually counted as species. But the beta diversity, or the addition of new units of diversity added by a new region, is decreasing. Beta diversity can be equated with the complementarity of different conservation areas, which was discussed earlier in the Chapter (Section 2.3). Identifying measures of diversity that can scale relates the local diversity of these systems to the global biodiversity that is being threatened. If a measure does not translate across taxon and regions, we cannot assess the relationship between local biodiversity loss and global biodiversity loss. In Chapter 5, we will discuss the issue of invasive species further, noting how global biodiversity measures can aid in deciding whether to invest in the control of invasive species.

Representativeness is critical for my account of biodiversity as it is quite revolutionary in that it jettisons some of the historical baggage of the term. If biodiversity is constituted by phylogenetic structure then it does not refer directly to the diversity of genes, or functional features, or ecosystems. My biodiversity realism then conflicts with some of the traditions of conservation science, which want to describe diversity across all these arrangements (I argue in Chapter 3 that ecological systems cannot be described through diversity measures). However, if phylogenetic structure is representative of alternative methodologies for describing biodiversity, then it is not as radical as it may seem on first pass.