Communities and Ecosystems

Abstract

Traditionally, communities are defined as the totality of all populations interacting in a joint habitat, i.e. living space. The term ecosystem includes the biologically relevant components of the living space, i.e. those components which determine living conditions and which are influenced themselves by the activities of the local communities. These activities include extraction of resources, disposal of wastes, and ecosystem engineering. A description of “community processes” includes birth rates, predation rates, death rates, etc., using individuals as currency to quantify processes. A description of “ecosystem processes” includes uptake rates, production rates, respiration rates using masses of chemical substances or energetic units for quantification. In spite of a long-lasting division between community- and ecosystems-centered research traditions, both ways of measuring and describing processes are only two sides of the same coin. Therefore, the community and the ecosystem perspective will be merged in this book.

Exercise Questions

The right-hand column of the table below indicates the place where the answer can be found, deduced logically from the information contained in the text, or calculated from the equations there.

	Question	Section
1	Distinguish the terms community and ecosystem	7
2	What is a metacommunity?	7.1.1
3	Explain the difference between the superorganism concept and the individualistic concept of communities and ecosystems	7.1.2
4	Which factors determine the species composition of a community?	7.1.2
5	What are connectance and link density?	7.1.3
6	How and why are species aggregated into guilds?	7.1.3
7	List at least 4 collective properties of communities	7.1.4
8	What is a trophic level?	7.2.1
9	Which trophic level do primary consumers form?	7.2.1
10	Does production necessarily decrease with trophic level? And why?	7.2.1
11	Does biomass necessarily decrease with trophic level? And why?	7.2.1
12	What is ecological efficiency?	7.2.1
13	How can DOC excreted by organisms become available for feeding by higher trophic levels?	7.2.2
14	Explain the microbial loop	7.2.2
15	Why has the concept of the food chain to be replaced by the concept of the food web?	7.2.2
16	How important is consumption of primary production by the microbial food web?	7.2.2
17	How is the importance of the microbial food web related to nutrient richness?	7.2.2
18	Why is the jelly food chain disadvantageous for the feeding of fish?	7.2.2
19	Compare freshwater and marine pelagic food webs with respect to the microbial food web, the mesozooplankton serving as food for fish and the jelly food chain	7.2.2
20	How does the trophic level of zooplankton feeding fish change with nutrient conditions?	7.2.2
21	Why is the energy transfer from the 1st to the 2nd trophic level in hard-bottom benthos often less efficient than in the pelagic?	7.2.2
22	Compare the importance of ecosystem engineers in the pelagic and in the benthos	7.3
23	How do perennial macrophytes influence the living conditions of organisms living within macrophyte beds?	7.3.1
24	Which guilds profit from giant kelps, which suffer disadvantages?	7.3.1
25	Explain the difference of the attachment modes of mussels and oysters	7.3.2
26	How do mussel reefs influence the fauna in intertidal flats in the vicinity?	7.3.2
27	Can reef-building oysters and mussels coexist? If yes, how?	7.3.2
28	Which groups of organisms are the dominant ecosystem engineers in coral reefs?	7.3.3
29	Are corals the only calcifying organisms in coral reefs?	7.3.3
30	Explain the role of parrotfish in coral reefs	7.3.3
31	Which types of organisms might overgrow reef-building corals and which ones protect them from overgrowth?	7.3.3
32	Explain coral bleaching	7.3.3
33	Which role do crown-of-thorns starfish play in coral reefs?	7.3.3
34	How can coral reefs have so much biomass and production in nutrient-poor seas?	7.3.3
35	Calculate Shannon’s and Simpson’s diversity index for the three following communities (A, B, C) from species relative abundances: A: sp 1: 0.5, sp 2: 0.3, sp 3: 0.1, sp 4: 0.05, sp 5: 0.0.5 B: sp 1: 0.3, sp 2: 0.3, sp 3: 0.3, sp 4: 0.05, sp 5: 0.0.5 C: sp 1: 0.3, sp. 2: 0.3, sp 3: 0.2, sp 4: 0.05, sp 5: 0.05, sp 6: 0.05, sp 7: 0.06	7.4.1
36	Explain the difference between α-, β-, and ϒ-diversity	7.4.1
37	Which factors determine the local species pool?	7.4.2
38	How can the latitudinal trend of diversity be explained? Offer several alternative explanations?	7.4.2
39	How does predation influence local diversity?	7.4.2
40	How does productivity influence the impact of predation on diversity?	7.4.2
41	How can we distinguish between the sampling and the complementarity effect of diversity on productivity?	7.4.3
42	Does diversity at one trophic level increase or decrease the top-down effect of the next higher trophic level?	7.4.3
43	Does diversity at one trophic level increase or decrease the top-down effect on the next lower level?	7.4.3
44	Explain the difference between constancy and persistence	7.4.3
45	What is the difference between resistance and resilience of a community?	7.4.3
46	Can we expect that diversity has the same effect on the stability of collective community properties and on individual populations?	7.4.3
47	What is the insurance effect of diversity?	7.4.3
48	What are the main differences between pioneer and late successional species?	7.5.1
49	What is the difference between succession and phenology?	7.5.1
50	How can we analyze successional sequences if succession time by far exceeds the lifetime of observers?	7.5.1
51	Can sea urchins influence macroalgal succession towards a kelp forest? If yes, how?	7.5.2
52	How do different herbivorous fish influence succession in a coral reef?	7.5.2
53	How do cover and depth penetration of macrophytes change during primary succession in a manmade lake?	7.5.2
54	Why is pelagic seasonality a mix of succession and phenology?	7.5.3
55	What are the conditions for the development of a spring bloom of phytoplankton?	7.5.3
56	Why is there often a phase of low phytoplankton biomass after the spring bloom?	7.5.3
57	How does summer phytoplankton succession in cold-temperate zones differ between eutrophic and oligotrophic systems?	7.5.3
58	How do unusually high and unusually low densities of zooplanktivorous fish influence the seasonal succession of phyto- and zooplankton in the cold-temperate zone?	7.5.3
59	What is the main difference between cold-temperate/boreal and warm-temperate/subtropical phytoplankton in winter?	7.5.3
60	How does the seasonal pattern of fish predation zooplankton differ between cold-temperate and Mediterranean lakes?	7.5.3
61	What is the reason for ice margin blooms of phytoplankton?	7.5.3

Glossary

α-diversity

local diversity

β-diversity

compositional difference between localities within a community

ϒ-diversity

regional species innventory

bacterivory

feeding on bacteria

biomass

mass of organisms

calcifier

organisms forming calcareous skeletal structures

carnivory

feeding on animal biomass

chronosequence

reconstruction of a successional trajectory from sites of different age (space-for-time substitution)

clear-water phase

mid-season phytoplankton minimum, usually caused by zooplankton grazing

community

sum of populations interacting within a joint habitat

somplementarity

difference in resource use and environmental tolerance of species leading to an improved performance of the community

constancy

absence of change of a state variable through time

coral bleaching

loss of endosymbiotic phototrophs by corals

cover

percent habitat area covered by organisms

detritivory

feeding on dead material

diversity

a combined measure of species number and even distribution of individuals between species

ecological efficiency

ratio between production rates of subsequent trophic levels

ecosystem

system composed of a local community and its physical, chemical, and geological environment

ecosystem engineering

modification of the physical structure of the environment by organisms

elasticity

ability of a community to return to the normal state after a perturbation

eutrophic

nutrient-rich environment

evenness

even distribution of individuals among species

facilitation model

assumption that early successional species prepare the ground for later species

food chain

sequence of predator–prey relationships, A is eaten by B, B by C, C by D, ..

food web

system of branching and connected food chains

foundation species

species with disproportionate high influence on a community, often an ecosystem engineer

guild

group of populations sharing the same resources and predators

herbivory

feeding on plant or algal biomass

individualistic concept

assumption that species are distributed individually in the environment

inhibition model

assumption that species of any successional stage inhibit the intrusion of later successional species. These can only establish if disturbance open opportunities.

jelly food chain

food chain with gelatinous links

kelp forest

macrophyte stands dominated by large brown algae

metacommunity

group of local communities connected by immigration and emigration of organisms

microbial food web

food web with unicellular participants

microbial loop

recycling of DOC to the food web by bacterial uptake of DOC and subsequent bacterivory

oligotrophic

nutrient-poor environment

overyielding

improved performance of a species mixture in comparison to the calculated mixed effect of single-species performances

persistence

longevity of a qualitatively defined community status (e.g., bivalve reef)

phenology

seasonal change in the appearance of a community caused by seasonally bound life cycle events of species

pioneer species

early successional species characterized by high dispersal abilities, high fecundity, short lifetime, and small size

primary production

production of organic matter from inorganic material

resilience

amount of perturbation which a community can tolerate and still return to normal

resistance

ability of a community to maintain its state in spite of perturbations

sampling effect

increased probability of having high performance species with increasing species richness

species–area curve

curve describing the relationship between the number of identified species and the sampled area

succession

replacement of species during the development of a community

superorganism

assumption of a tight integration of communities leading to joint distributions of species, self-regulation, and optimization at the community level

tolerance model

assumption that late successional species first tolerate and then overcome the competitive pressure by early successional species

trophic level

group of organisms with the same position in the food chain