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Macroecology

Daijiang Li

LSU

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Announcements

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What is Macroecology?

Macroecology is a way of studying relationships between organisms and their environment that involves characterizing and explaining statistical patterns of abundance, distribution, and diversity. Jim Brown 1995

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the prefix "macro" for two reasons. 1) in order to characterize patterns in the statistical distributions of variables among individuals, populations, or species, it is usually necessary to work at relatively large spatial and/or temporal scales so as to obtain sufficiently large samples. 2) in order to investigate the implications of important advances in other disciplines such as biogeography, paleo-biology, systematics, and the earth sciences, it is necessary to expand the scale of ecological research.

Macroecology differs from most of recent and current ecology in its emphasis on statistical pattern analysis rather than experimental manipulation

McGill, Brian J. "The what, how and why of doing macroecology." Global Ecology and Biogeography 28.1 (2019): 6-17.

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View 1: Macroecology = the ecology of large scales

How large is large enough? Extent? Grain?

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View 1: Macroecology = the ecology of large scales

The dimensionality of macroecology. Figure taken from McGill (2019) https://doi.org/10.1111/geb.12855.

The dimensionality of macroecology. Figure taken from McGill (2019) https://doi.org/10.1111/geb.12855.

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View 1: Macroecology = the ecology of large scales

Macroecology does not require to be big simultaneously in all dimensions

Large needs to be defined relative to the organisms involved.

Notion of dozens: dozens of generations (time), population (space), species (taxa)

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View 2: Macroecology = a statistical, emergent, non-reductionist approach

Macroecology is a big-picture, statistical approach to the study of ecology. By focusing on broadly occurring patterns and processes operating at large spatial and temporal scales and ignoring localized and fine-scaled details, macroecology aims to uncover general mechanisms operating at organism, population and ecosystem levels of organization. Smith et al. 2008

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In the reductionist view, adequate modelling of the components should always reproduce all emergent phenomena.

View 2: Macroecology = a statistical, emergent, non-reductionist approach

The transmutation problem: scaling up is challenging because of Jensen's inequality (the average of a function is not the function of the average) f(xi)¯≠f(xi¯)

jensens inequality

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View 2: Macroecology = a statistical, emergent, non-reductionist approach

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the claim that macroecology can be explained by individuals and population dynamics can be demonstrated rigorously to be possible only rarely, owing to the transmutation problem

View 3 by McGill 2019

Macroecology is the study at the aggregate level of aggregate ecological entities made up of large numbers of particles in the pursuit of generality

view3

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Macroecological 'laws'

  • Species richness

  • Species Range

  • Body size

  • Abundance

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What do you expect the relationship between species richness and area to be?

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Species-area relationships ( S=cAz )

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Species-area relationships

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The theory of Island Biogeography

It attempts to explain the colonization and extinction of species (and subsequently the species richness of islands) as a function of island area and distance from the mainland

Early naturalist-explorers noted that large islands hold more species than small islands

  • Captain Cook (1772–75). P. Darlington: “on islands, a tenfold increase in land area leads to a doubling of the number of species”

Apply theory to terrestrial (or aquatic) patches.

Vegetation patterns across the landscape (patches) suggest islands of different sizes

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The theory of Island Biogeography

Equilibrium species richness (S) is affected by the distance of the island from the mainland, and size of the island

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19.13The number of species established on an island represents a dynamic equilibrium between the immigration of new colonizing species and the extinction of previously established ones Species on the mainland are the possible colonists to an uninhabited island The species with the greatest dispersal ability will be the first to colonize the island The immigration rate will decline as the number of species on the island increases Few “new” species left to colonize The immigration rate will be zero when all mainland species exist on the island

The theory of Island Biogeography

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The theory of Island Biogeography

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The theory of Island Biogeography

This theory also applies to organisms living in patches!

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Island Biogeography AND Landscape Patches

“A patch of habitat isolated from similar habitat by inhospitable terrain may be considered an island”

  • Mountaintops
  • Bogs
  • Ponds
  • Dunes
  • Areas fragmented by human land use
  • Individual hosts of parasites
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Latitudinal gradients in species richness

Latitude gradient of biodiversity Mannion et al. 2014

This pattern of increasing species diversity from the poles to the tropics is remarkably consistent across numerous marine and terrestrial taxa (plants, fish, birds, mammals, and many invertebrate groups) and has also persisted across much of both modern and deep time.

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Distribution of extant terrestrial vertebrate species showing the high concentration of diversity in equatorial regions

Hypotheses

Speciation and extinction rates determine species richness

  • Climate: high solar energy, low seasonality --> high productivity --> high species richness (recall foodweb)

  • Historical: more time, less perturbed in the past by climatic events, accumulating species over time

  • Geographic: larger and more heterogeneous areas in tropics

  • Mid-domain effect: bounded geographical domain + random shifting species ranges --> mid-domain peak of species richness. Null models

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Hypotheses

Speciation and extinction rates determine species richness

  • Climate: high solar energy, low seasonality --> high productivity --> high species richness (recall foodweb)

  • Historical: more time, less perturbed in the past by climatic events, accumulating species over time

  • Geographic: larger and more heterogeneous areas in tropics

  • Mid-domain effect: bounded geographical domain + random shifting species ranges --> mid-domain peak of species richness. Null models

Not mutually exclusive

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Hypotheses

Speciation and extinction rates determine species richness

  • Climate: high solar energy, low seasonality --> high productivity --> high species richness (recall foodweb)

  • Historical: more time, less perturbed in the past by climatic events, accumulating species over time

  • Geographic: larger and more heterogeneous areas in tropics

  • Mid-domain effect: bounded geographical domain + random shifting species ranges --> mid-domain peak of species richness. Null models

Not mutually exclusive

Elevational gradient

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If species' ranges are randomly shuffled within a bounded geographical domain free of environmental gradients, ranges overlap increasingly toward the center of the domain, creating a “mid‐domain” peak of species richness.

Species range

Range size distribution (small spatial scale)

Range size distribution (larger spatial scale)

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Spatial variation in range size

Rapoport's rule: the tendency for species living at higher latitudes to have larger range sizes

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  • Niche breath and inter-specific interactions: stronger competition in tropics leads to narrower niche; or more controlled by predators, parasites, and pathogens

Body size

Body size distribution

bodymass

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Multiplicative by nature: Why logarithmic transformation is necessary in allometry

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Spatial variation in body mass

Bergmann's rule: the tendency for a positive association between the body mass of species in a monophyletic higher taxon and the latitude inhabited by those species.

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Phylogeny I : Random ancestral colonization by a large-bodied species Phylogeny II: Selective advantage of traits which are accidentally coupled with large body size Dispersal ability: Small body mass is associated with low dispersal ability Heat conservation: Increased heat conservation of large-bodied species; the higher surface area to volume ratio of smaller individuals results in improved heat dissipation in hot environments Starvation resistance: Increased starvation resistance of large-bodied species

Evidence for Bergmann's rule is mixed

Riemer, Kristina, Robert P. Guralnick, and Ethan P. White. "No general relationship between mass and temperature in endothermic species." Elife 7 (2018): e27166.

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Species-abundance distributions (SAD)

The species abundance distribution (SAD) characterizes the distribution of abundances of all species within a sample or ecological community.

Histogram of abundance

Rare species are common; common species are rare

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Species-abundance distributions (SAD)

The species abundance distribution (SAD) characterizes the distribution of abundances of all species within a sample or ecological community.

Histogram of abundance

Rare species are common; common species are rare

Rank abundance distribution

Species richness and evenness

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Understanding the abundance and distribution of species is arguably one of the most fundamental goals of ecology.

Abundant-center hypothesis

The abundant center hypothesis states that species density should be highest in the center of species range

Dallas et al. 2017

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Evidence for Abundant-center hypothesis is mixed

Dallas, T. A., Santini, L., Decker, R., & Hastings, A. (2020). Weighing the Evidence for the Abundant-Center Hypothesis. Biodiversity Informatics, 15(3), 81-91.

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Macroecology in an era of rapid change

How would environmental changes such as climate change, land use change, and biological invasions affect species range, abundance, body size, and diversity, and ultimately, the human society?

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Announcements

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