Ecosystem Ecology   III. Productivity, Diversity, and Stability

2 million named, 10-30 million out there….

But do we NEED all these species??

There’s a lot of redundancy in nature… http://katherinegerdes.com/portfolio/11/rainy-day-jewels

Are all species equally important? If not, which ones are critical?

with without

What does biodiversity do??

A. Productivity 1. Gross Primary Productivity Total photosynthetic productivity; CO2 + H20 -----> Glucose + O2

A. Productivity 2. Net Primary Productivity NPP = GPP - respiration (Plants use some of the energy they absorb; it is not stored as biomass. NPP is only the amount stored as new biomass.)

B. Diversity - Relationships with Productivity 1. Productivity increases diversity

B. Diversity - Relationships with Productivity 1. Productivity increases diversity - QUANTITATIVE EFFECT If you have more productivity at the base of a food web, then you can build a longer food chain (adding additional levels AND species)….

B. Diversity - Relationships with Productivity 1. Productivity increases diversity - QUALITATIVE EFFECT An increase in productivity may also occur because more types of food have been added. This may allow for more specialization at the next trophic level - and the coexistence of more species.

B. Diversity - Relationships with Productivity 1. Productivity increases diversity 2. Diversity increases productivity

- Sampling Effects More diverse communities are more likely to contain the most productive species, and thus raise the total productivity.

- Niche Complementarity More diverse communities are more likely to contain different types of species that use different types of energy... thus more efficiently harvesting the available energy

Monoculture Polyculture They all need the same things at the same concentrations; have to place them far apart to reduce competition. Combinations of different plants can be planted at higher density, and they use different "niches" and coexist. Even if abundance of "most productive" species, drops, this loss can be offset.

- Positive Interactions More diverse communities may contain species that benefit other species, and thus increase the productivity of the whole community

Monoculture Polyculture without beans with beans They all need the same things at the same concentrations; have to place them far apart to reduce competition. Nitrogen fixing legumes (beans) nutrify the soil, increasing the growth of other plants

Diversity and Productivity in a Long-Term Grassland Experiment Tilman, et al. 2001. Science 294. 843 - 845 Cedar Creek Ecosystem Science Reserve - 168 9 m x 9 m plots - 1, 2, 4, 8, or 16 species randomly chosen from a pool of 18 species: 4 species, each, of C4 grasses, C3 grasses, legumes, non-legume forbs; 2 species of woody plants. - ~35 replicates of each treatment

Diversity and Productivity in a Long-Term Grassland Experiment Tilman, et al. 2001. Science 294. 843 - 845 Dotted line is biomass in a monoculture of the most productive species. Higher productivity than this, at higher richness values, means niche complementarity or positive effects must be occurring.

Diversity and Productivity in a Long-Term Grassland Experiment Tilman, et al. 2001. Science 294. 843 - 845 Dotted line is biomass in a monoculture of the most productive species. Higher productivity than this, at higher richness values, means niche complementarity or positive effects must be occurring. So, many random assemblages of multiple species have biomass above that of the most abundant monoculture (can’t just be sampling effect).

Diversity and Productivity in a Long-Term Grassland Experiment Tilman, et al. 2001. Science 294. 843 - 845 Dotted line is biomass in a monoculture of the most productive species. Higher productivity than this, at higher richness values, means niche complementarity or positive effects must be occurring. So, many random assemblages of multiple species have biomass above that of the most abundant monoculture. And we might expect greater niche complementarity in natural systems…

Additional Experiments and Results: - Foliar fungal disease incidence decreased at higher diversity because of greater distance between individuals of a species, and resultant lower rates of disease spread (Mitchell et al. 2002). (“Dilution Effect”) - Greater plant diversity led to greater abundance and diversity of herbivorous insects, and this effect continued up the food web to predator and parasitoid insects (Haddad et al. 2001). (“Qualitative Effects of Diversity”)

Additional Experiments and Results: - Fewer novel plant species invaded higher diversity treatments because of their lower soil NO3 levels, greater neighborhood crowding and competition, and greater chance that functionally similar species would occur in a given neighborhood (Figs 3; Naeem et al. 2000, Kennedy et al. 2002, Fargione et al. 2003, Fargione and Tilman 2005a, 2005b). Greater plant species numbers led to greater ecosystem stability (lower year-to-year variation in total plant biomass) but to lower species stability (greater year-to-year variation in abundances of individual species), with the stabilizing effect of diversity mainly attributable to statistical averaging effects and overyielding effects (Fig 4; Tilman et al, submitted). Data gathered this past field season shows that soil total C has now become an increasing function of plant species numbers (Fig 5).

Additional Experiments and Results: - Greater plant species numbers led to greater ecosystem stability (lower year-to-year variation in total plant biomass) but to lower species stability (greater year-to-year variation in abundances of individual species).

Additional Experiments and Results: - Stored soil carbon increases with diversity.

C. Effects on Stability

C. Effects on Stability 1. Types - "resistance to change" - "resilience after change"

C. Effects on Stability 1. Types 2. Relationships with diversity - more diverse communities are less susceptible to single "types of disturbance" - (a pest, a flood, a drought) - because the many species are unlikely to be sensitive to the same thing.

C. Effects on Stability Biodiversity and Ecosystem Functioning: Current Knowledge and Future Challenges. Loreau, et al. 2001. Science 294: 804 - 808 As richness increases, productivity become less variable (more stable).

C. Stability 1. Types 2. Relationships with diversity - diverse communities may recover more rapidly, too (resilience).... but they may not. Fisheries ... yes Rain forest... maybe not

Rainforests feed themselves and water themselves. Stimulate condensation and precipitation Volatiles released Rainforests feed themselves and water themselves. Decomposition rapid Absorption rapid

Nutrient runoff… then reduced rainfall INCREASE FIRE CUT FOREST DOWN Select for fire-adapted grasses.... rainforest doesn't come back.... Nutrient runoff… then reduced rainfall INCREASE FIRE

"Multiple Stable States" RAINFOREST (wet, few fires) "Multiple Stable States" GRASSLAND (dry, many fires)

We are dependent on the environment for food and resources We are dependent on the environment for food and resources. Ideally, we would like a STABLE, PRODUCTIVE supply of these resources.... right?? FEAST FAMINE

(We don't want "boom and bust", "feast and famine" scenarios....)

We are dependent on the environment for food and resources We are dependent on the environment for food and resources. Ideally, we would like a STABLE, PRODUCTIVE supply of these resources.... right?? (We don't want "boom and bust", "feast and famine" scenarios....) STABILITY ? PRODUCTIVITY

We are playing jenga with our life support systems... de Ruiter et al. 2005. Food Web Ecology: Playing Jenga and Beyond Science 309:68 - 71

But what else does biodiversity do??

2) Biodiversity improves ecosystem services Estimates of various Ecosystem Services - $U.S. trillions Ecosystem services Value (trillion $US) Soil formation 17.1 Recreation 3.0 Nutrient cycling 2.3 Water regulation and supply Climate regulation (temperature and precipitation) 1.8 Habitat 1.4 Flood and storm protection 1.1 Food and raw materials production 0.8 Genetic resources Atmospheric gas balance 0.7 Pollination 0.4 All other services 1.6 Total value of ecosystem services 33.3 Source: Adapted from R. Costanza et al., “The Value of the World’s Ecosystem Services and Natural Capital,” Nature, Vol. 387 (1997), p. 256, Table 2. TOTAL GLOBAL GNP (1997) = 18 trillion.

GLOBAL GDP 2011: $75 trillion

Based on different criteria, this is the ecosystem value we lost in that 14 year span. GLOBAL GDP 2011: $75 trillion

3) Aesthetics and Inspiration: Biodiversity enriches our cultures

3) Aesthetics and Inspiration: Biodiversity enriches our cultures

4) Fights Disease Lyme Disease: - fragmentation reduces patch size - abundance of predators like fox declined - white-footed mice (host of Borrela burgdorferi bacterium) increase. - increase host density, increase infection rate of ticks.

High Relative Abundance of Hosts Low Relative Abundance of Hosts West Nile Virus Low Diversity: High Relative Abundance of Hosts High Diversity: Low Relative Abundance of Hosts Transmission rates to humans are higher in less diverse systems Swaddle and Carlos, 2008. PLoS one 3:e2488

Intrinsic Value Utilitarian Why Preserve Diversity/Nature? Ecosystem Services?