5 Habitat Loss and State Shifts

Question 1

Global habitat losses
(so far)

Answer 1

• 30 percent of (seagrasses) are lost
• 50 percent of coastal wetlands are filled, ditched or drained
• 75 percent of coral reefs are threatened and 25 percent are degraded
• 85 percent of oyster reefs been overfished, dredged away, buried with sediment or made unproductive by pollution, diseases and changes to river flows

Question 2

habitat

Answer 2

predominant features that create structural complexity in the environment, such as plants (e.g., seagrass meadows, kelp forests), animals (oyster reefs), or other geological features (e.g. rocky reefs, mudflats)

Question 3

loss

Answer 3

measurable reduction in habitat abundance and distribution

Question 4

habitat loss

Answer 4

often manifests as a long-term shift from complex to simple habitats
- significant change to the distribution, abundance, functioning, and species identities within a particular area
- e.g. seagrasses to soft-sediments or macroalgal canopies to turfs

habitat degradation and fragmentation are often a precursor to habitat loss

Question 5

Long-term regime shifts

Answer 5

• duration of shift depends on recruitment, altered environmental conditions, and human intervention
• ‘long-term’, when a shift persists beyond the life-cycle of the key species
• the concept of shift is related to the concept of tipping-point and resilience and to stability theory in general

Question 6

disturbance

Answer 6

• discrete and localized event that determines the removal of individuals from the population/community and creates the opportunity for new individuals to settle
  → frees up resources, mitigating the intensity of competition, and leads to a secondary succession (patch dynamics)

Question 7

stress

Answer 7

refers to those external (cronic) factors that preclude or limit the productivity and growth of a population/community (sublethal)

Question 8

perturbation

Answer 8

any relatively discrete event over time that disrupts the structure of an ecosystem, community or population and alters resources, substrate availability or the physical environment
- pulse or press perturbations

Question 9

concept of stability

Answer 9

• system in a steady state if
  –> the variables that define the behavior of the system (=state variables) are unchanging in time
  –> the processes are unchanging in time
• stability = property of a system to maintain or return to the original steady state when disturbed
• one of the most important ecosystem properties in ecology

Question 10

ecological stability

Answer 10

• property of a natural system to apply self-regulating mechanisms
• to maintain or return to the original steady state when disturbed from a condition of equilibrium

Question 11

resistance

Answer 11

a stability that indicates the ability of an ecosystem to resist perturbations (disturbances) and to maintain its structure and function intact

((resistance-disturbance))

Question 12

resilience

Answer 12

a stability that indicates the ability to recover when the system has been disrupted by a perturbation

((resilience-recover))

Question 13

Resistence vs Resilience

Answer 13

evidence suggest, that these two kinds of stability are mutually exclusive –> difficult to develop both at the same time

Question 14

expectations of resistance and resilience at ecosystems in benign physical environments

Answer 14

• more resistente stability
• less resilience stability

Question 15

expectations of resistance and resilience at uncertain physical environments

Answer 15

• more resilience stability
• less resistance stability

Question 16

measuring stability

Answer 16

• complex
• response can involve
  –> structural parameters (biotic/abiotic, species diversity, habitat availability…)
  –> functional characteristics (productivity, nutrient cycling)
  –> socio-ecological parameters (ecosystem service provisioning)
• ecosystems can be stable in some of their properties and unstable in others

Question 17

possible stability change of a system affects ___ ?

Answer 17

the capability to respond to the same type of perturbations

Question 18

effects / consequences of repeated perturbations

Answer 18

• if a population is stable it is able to recover after each disturbance before the next
• a less stable population has not enough time to recover before the next disturbance –> can be driven to extinction
• if disturbances are occurring further apart, a less stable population is able to recover from the same magnitude of disturbance

Question 19

Varying resilience levels of an ecosystem function (Ψ) to environmental perturbations

Answer 19

shows a system with
-high resistance
-slow recovery

Question 20

Varying resilience levels of an ecosystem function (Ψ) to environmental perturbations

Answer 20

shows a system with
- low resistance
- rapid recovery

Question 21

Varying resilience levels of an ecosystem function (Ψ) to environmental perturbations

Answer 21

shows a system with
- low resistance
- slow recovery

Question 22

lack of resilience

Answer 22

• vulnerabilty
• can be quantified as the length of time that ecosystem functions are provided below some minimum threshold (set by resource managers) up to total deficit of ecosystem function

Question 23

state shifts

Answer 23

disturbances of sufficient magnitude or duration can force an ecosystem to pass a threshold beyond which a different regime of structures and processes predominates

–> the state of the ecosystem shifts

Question 24

possible types of ecosystem responses to external perturbations

Answer 24

• if the feedback loops are very strong –> no going back anymore

b) almost linear

Question 25

Answer 25

• the stability is shape
• we have a certain state “embedded” in a certain stability, then a threshold (hill in shape) then shift into other state
• how can it happen? –> human activities lower resilience (threshold)
• before: had a high resilience (hoher Hügel, den Kugel die Kugel (state) überwinden muss)
• ball (state) follows that pathway
• shift to another state depends on the pressure

Question 26

system shift as consequence of press (stress) perturbations

Answer 26

if as environmental condition surpasses a threshold
–> stress increases (red arrow)
–> change in ecosystem state can be large and disproportional (blue arrow)

Question 27

system shift as consequence of pulse (disturbance) perturbations

Answer 27

• under constant environmental conditions, the ecosystem can undergo a drastic change in state (red + blue arrow) if disturbance effect magnitude (red arrow) is large enough
• a larger disturbance effect is needed to get the drastic change when the ecosystem is less stressed

graph as an example of what happens due to climate change
because we push the system even if we haven’t done any more damage

Question 28

Answer 28

versteh ich nicht so ganz

Question 29

erosion of resilience due to human impact

Answer 29

• can lead to very rapid ecosystem shifts
  e.g. by
  1) removing functional groups of species (top down effect)
  2) emissions of waste and pollutants (bottom-up effects)
  3) alteration of natural disturbance regimes

figure:
I: state in a diversity of ecosystem
II: state alternates and looses resilience because of a named human impact (erosion of resilience)
III: then due to triggers (as named) the regime shifts (=changes in structure or function of ecosystems)
–> rapid process because earlier (II) human impact erased resilience
IV: ecosystem shift in alternate state

Question 30

can resistance and/ or resilience be increased again?

Answer 30

• yes, due to protection (from human pressures)

Question 31

effects of functional redundancy on resilience of ecosystem functions

Answer 31

• when multiple species perform similar functions –> redundancy between the species in their contributions to ecosystem processes
• if those species have differing responses to environmental perturbations –> higher resistance go ecosystem function

–> “insurance effect” of biodiversity

Question 32

what is a “protection paradox”?

Answer 32

• loss of species due to disturbance in MPA (Marine Protected Area) and outside MPA
• species loss in MPA higher than outside
  -healthy ecosystems are more resilient

Question 33

What are the consequences of habitat loss?

Answer 33

• loss of physical complexity
• loss of facilitated species
• loss of food resources
• loss of functional diversity
• expansion of invasive species
• biotic homogenization
• loss of ecosystem services

Question 34

Loss of physical complexity (consequence of habitat loss)

Answer 34

the loss of physical engineers (e.g. seagrass) leads to:
- fragmented landscapes and even local extinction
- reduced potential for recruitment and recovery (fewer adults to produce gamets, space competition)
- altered local environment e.g. gorgonians loss and increased sediment stability)

Question 35

physical engineers

Answer 35

organisms that strongly shape the physical environment
- light conditions
- hydrodynamics
- sedimentation
- shelter and refuge

e.g. seagrass

Question 36

loss of facilitated species (as consequence of habitat loss)

Answer 36

• loss of many species because they depend on their biogenic habitat

Question 37

the loss of food resources (consequence of habitat loss)

Answer 37

• losses can cascade through the system and alter food webs and other species interactions
• effects can cascade through to humans (e.g. fisheries)

Question 38

loss of functional diversity (consequence of habitat loss)

Answer 38

the loss of species is not randomly distributed among ecological and functional categories (top-down)

–> loss of ecological functions can be disproportionately greater than what would be predicted from a decline in species richness

(loss ecological functions > loss of species)

Question 39

expansion of invasive/noxious species (consequence of habitat loss)

Answer 39

• possible expansion of “invaders”
• empty system –> new species come and replace old ones
• there is a trend towards smaller forms with generalist, opportunistic and/or invasive traits

Question 40

biotic homogenization
(consequence of habitat loss)

Answer 40

due to reduction in
- overall structural complexity
- native biota
- functional traits
–> expansion of few widespread and less complex but broadly tolerant biota

Question 41

loss of ecosystem services (consequence of habitat loss and homogenization)

Answer 41

e.g. loss of
- primary productivity
- nutrient cycling
- carbon sequestration
- maintenance of regional diversity

• some of these services provided by biogenic habitat-formers, others by facilitated species
• small habitat losses can often be tolerated
• large losses can change ecology of e.g. entire coasts

Question 42

natural recovery / passive restoration

Answer 42

• process by which an ecosystem returns to a prior state following the cessation of some impact or alteration
• system is able to fully recover

Question 43

disturbance and recovery mechanisms

Answer 43

• recovery can be very different from the response to a disturbance
• processes that control disturbance and recovery determine the vulnerability of an ecosystem
• if NOT easily disturbed: resistant ecosystem, resilient ecosystem if recovery is quick
• recovery is often a slow process (decades to centuries)

Question 44

novel ecosystems

Answer 44

Concept elaborated by Hobbs et al. (2009):
- varying degrees of alteration of abiotic and /or biotic components result in systems that move far away from their historical configuration and dynamics
- result is: different configurations
- there’s levels of change as (1) hybrid state with moderately changed systems and (2) novel state with extensively changed systems
- idea of the concept: theat there are thresholds (ecological and social) that effectively prevent the return of the system from a novel state to a less altered state

Question 45

How to value novel ecosystems?

Answer 45

• some provide a continuation of benefits to people
• may provide new and improved benefits to people
• if properly managed they can provide increased resilience and conservation capacity in a rapid changing world

Question 46

why is Hobb’s concept contentious? (umstritten)

Answer 46

• can be seen as inevitable or necessary consequence of the challenges and opportunities facing conservations
• some fear that it can be seen as “license to trash” nature or as a “get out of jail free card” for prospective harmful developments

Question 47

consequences of shifting baselines

Answer 47

• a baseline is a reference point from the past (how things used to be)
• if we allow the reference points of the baseline to shift, we loose track of our standards
• they reduce expectations of scientists and managers
• we eventually accept the degraded state as being natural

Question 48

Active restoration

Answer 48

actions included in process of assisting recovery are
- acceleration and enabling of the recovery when natural recovery process is slow or lack
- forming functional and healthy ecosystems (can differ from “pre-human-times”) and enabling the renewal of services –> forming a “target-designed novel ecosystem”