Population Ecology I. Distribution & Abundance of Populations & Species. Topics:

Transcription

1 Population Ecology I Distribution & Abundance of Populations & Species Molles & Cahill (2008) Chapter 10 Topics: Population Ecology defined Population defined Issues: Population distribution Clumped Random Regular Population density Population abundance Rarity and Vulnerability to extinction (practical applications in conservation biology, pest control)

2 Population ecology Addresses the distribution, abundance, and density of populations. Addresses population structure and dynamics Addresses interactions between organisms (e.g. competitive, exploitative, mutualistic interactions). Defines community structure in terms of these interactions. Supported by evolutionary theory & ecophysiology. Population defined A group of potentially interbreeding individuals of a single species A group of individuals of a single species inhabiting a specific area. Highly localized group of individuals representing a fraction of the total population of a species, or All of the individuals of a species across its entire range.

3 Links to evolutionary theory (review Chapter 4) Links to physiological ecology (much of what we have covered) Common garden & transplant experiments (Clausen, Keck & Heisey 1940) This classic study design distinguishes acclimation from adaptation and helped define the concept of ecotype (c.f. genotype). Molles (2008) Chapter 8, p188

4 Tolerance limits central theme in population ecology but note that population ecology also considers biotic aspects (e.g. species interactions) Population distribution Distribution limits (range) often defined by physical factors. Range of three kangaroo species in Australia. These species ranges can be defined by environmental conditions, but biotic factors may also be involved. Fig. 10.2, Molles & Cahill, 2008

5 Tiger beetle distribution limited to cool environments Suggests clear physical & physiological tolerance limits Figs & 10.4, Molles & Cahill, 2008 Leaf Pubescence (hairs) why be hairy? (many reasons!) Glandular hairs (trichomes) on Cannabis sativa

6 For example, leaf pubescence can greatly reduce a leaf s radiation load and reduce it s evaporative water loss Pubescent leaves of Salvia apiana Photos: Dwight Beltz Cross-section of S. apiana (note abundant leaf hairs) Species often distribute themselves along climatic (temperature or moisture) gradients. Fig Molles & Cahill 2008

7 Within a region, species may further subdivide their ranges by microclimate Ehleringer et al. have shown that pubescence in Encelia sp. (wild sunflower) leaves follows environmental conditions (microclimate). Figs & 10.7, Molles & Cahill, 2008 Molles 2008

8 Intertidal region Zonation the result of both physical and biotic factors Molles 2008 Zonation in the intertidal - Barnacle species have different ranges (work of Connell Demonstrated that Balanus sp. is more vulnerable to dessication than Chthamalus sp.) Zonation among barnacles in the upper intertidal appear to be the result of both abiotic factors (tolerance limits) and biotic factors (competition) Figs & 10.9, Molles & Cahill, 2008

9 3 types of species distribution: Random Regular Clumped Again, both biotic and abiotic factors may determine the pattern. Fig , Molles & Cahill 2008 Behavioral interactions (aggression) may affect distribution (example from field studies of stingless bees) Molles 2008

10 Distribution patterns of Creosote bush change over time as shrubs grow (due to resource limitations) Molles 2008 Mature creosote bushes partition the soil habitat to avoid competition for soil resources (Evidence that both biotic and abiotic factors determine plant distribution) Molles 2008

11 Distribution varies with scale At large scales, organisms distributions tend to be clumped based on resource availability. At smaller scales, species interactions (e.g. competition) may result in habitat partitioning Warbler Feeding Zones Fig. 1.2 Molles & Cahill 2008 MacArthur found that warblers were able to coexist by feeding in different zones of trees (habitat or niche partitioning). Morse (1980) found that aggression between warbler species maintained their distinctive feeding zones.

12 Crow distribution over the continental US note clumping (compare to figure 10.15, Molles & Cahill 2008) Molles 2008 Bird populations tend to concentrate around key resources (food, habitat). Fig , Molles & Cahill, 2008

13 Plant species tend to be distributed along environmental gradients according to physical factors (Whittaker et al. ) Santa Catalina Mts. Arizona Great Smoky Mts. Tennessee Figs & 10.18, Molles & Cahill, 2008 Population Density Often linked to organism size suggesting resource limitations Fig , Molles & Cahill, 2008

14 Animal size vs. population density Fig Molles & Cahill 2008 Plant size vs. population density These size-density patterns suggest competition for resources influences population density Fig , Molles & Cahill, 2008

15 Rarity and vulnerability to extinction Rabinowitz (1981) defined 3 factors influencing commonness/rarity: Geographic range (extensive vs. restricted) Habitat tolerance (broad vs. narrow) Local population size (large vs. small) Species become more vulnerable to extinction if these 3 factors are combined See fig See fig b but extinction can easily occur even if one of these factors is strong enough (see next example). Fig , Molles & Cahill, 2008

16 Example of the passenger pigeon (Ectopistes migratorius) - Huge population sizes (billions), and broad range Former range of the passenger pigeon but had a very specific nesting requirement (old growth forests) Ectopistes migratorius the Passenger Pigeon Ça n existe plus!

17 Practical applications of population ecology: 1) Pest control 2) Species conservation We can apply principles of population ecology to manage populations more effectively (reduce populations of unwanted individuals or enhance population levels of desired species).