BIOL214 Ecology- Bilton

Question 1

What is a community?

Answer 1

A set of species co-occuring at a particular place and time

Question 2

Assemblage

Answer 2

used interchanged with community
but applies to a taxanomic group (

Question 3

community ecology

Answer 3

focuses on nature of predation, disturbance and consequences of competition
(small scale perspective)

Question 4

How does the community assemble of a location build up over time?

Answer 4

.evolution of new species
.dispersal from other locations

Question 5

Process that can lead to diversity

Answer 5

speciation
how one lineage becomes 2, responsible for diversity on earth

but diversity of lineages/ genetically divergence usually assosicated with ecological differntation- occupy different divergent niches.

immigration due to dispersal:
example:
beetle with active flight

consider how things move between localities
example: terrestrial insects- larval dispersal phase

Question 6

Consider local communities and regional species pool

Answer 6

example: take a rocky shore
individual shores (rock) home to communites
but think of individual out cropping consider it as harbering local communityt that sit within a reginal species pool so all species that live within the overall area
(small in a big)

diagram shows individual localites in red and arrows show dispersal in regional pool of species

Question 7

How does an individual patch effect a regional pool?

Answer 7

usually positively correlated local species richness and global species richness (more species in this the more potential)

alpha diversity and gama diversity

Question 8

Why study islands?

Answer 8

hawaian arcapeligo-

why study islands?
easy to dictate where the edges are (boundaries)

result of isolation typically have fewer species then main land ( look at simialr island size, same latitude on mainland)

less species= easier to get everything (practical)

replicated natural communties

Question 9

Rules to community assembly?

Question 10

Islands and source pools

Answer 10

if dispersal range is shorter between source island- most things there will be able to get (ocean currents, active transport)

distance between island and source if its far away (example: )
so far away from source of coloists things will be isolated for a long time witout anything else will get there- therefore speciation will occur in situ.

Question 11

Isolation is relative

Answer 11

ferns are common on even isolated islands and same species as other places, their dispersal phase means they can disperse huge distances (taxa dependant what= isolated)

endemics if old and isolated (not good at dispersing)

Question 12

Theory (model) of island community assembly and dynamics

Answer 12

Mccarthur and wilson (1967)

Produces a simple model, dynamic balance between immigration/extinction or speciation and extinction

Point of crossing- equilibirum number of species on island (dynamic balance)

Why?
immigration seems curved as rate falls off when dispersal colonise-
good diperses come first- immegration falls once the amount of species in source pool runs out.
extinction increase? more compitiion for resources

interspecfic interactions drive extinction

Question 13

Predicitions of the model (4)

Answer 13

Large islands have more species then small
(species are relationship)

Species richness declines with remoteness
(harder to reach lower immigration rates)

Number of species relatively constant through time

(unique prediction) Number of species composition will have a turnover through time. Actual species will change but the number will remain relatively constant.

Evidence of turnover is the key

Question 14

Study example (Simberloff and wilson)
Mangrove islands

Answer 14

They defornated small mangrove islands using big canvas tents, lots of different sizes and fogged islands with insectise collected what was present.

look at fauna pre- releative number of species is about the same as what it had before for all sizes.
same amount but different species composition (sets of species change, as what arrives is by chance)

Why?
rapid immagration

Question 15

relevant paper:

Question 16

Adaptive radiation

Answer 16

Series of diversification events from a common ancester

long view: fossil record
dinosaurs- radiation in fossil record of body types, thus diversity in ecological roles.

regional and global diversification

Question 17

mammal diversification

Answer 17

most dino death- molecular data can show mammal diversifcation (group timings etc)

Question 18

Empty niches/ difficult to occupy

Answer 18

Adaptive radation my be causation in far off isalnds because they’re occupy and fitting the new niches through changing

example: gala finches- using resources that on the mainland others would be occupying- woodpecker and finch with a stick.

Question 19

Example of adaptive radiation

Answer 19

Stickleback fish- found in coastal water and northern hem, rivers and lakes.
spines on back (3) anti predator device
an adnadromous fish- can live in various water like salmon, elaborate courthsip males build nest and care for eggs after getting the lady fish

Landlocked populations living in freshwater systems- show morpholigical mods compared to ancestrial ones

top fish has predators and the bottom doesnt- large difference in bony plates

Question 20

Paxton lake (Stickle back)
2 ways of being a stickleback

Answer 20

Limnetic-feed largerly on plankon in open water, slim grassile fish, small mouth.

Benthic fish, fresh water isopods, insect larave in the sediment (grub around)
larger bodied bigger head, gap, body size. With signfigant morphological differences

radation in to 2 species (max of 12,000 to do so)

Are they 2 different species? They are behaving as so
Genetically very similar- no hybrids in nature- they nest and mate in the same place- but avoid mating with the other type (go for the specfic red colouration)

Can hybridze within the lab

Different lakes show the same thing has happened

Question 21

How did now landlocked populations come to colonise?

Answer 21

canada- 12,000, created by land up lift at the end of glaciation
ice caps melt- sea levels rise- continents starts to rebound and raises up again from the new sea floor.

sea level rise and fall (scandanavia)

Question 22

eustacy vs isoctacy

Answer 22

Eustatic sea level rise- melting of ice caps

Isostacy- reposition of land once its lost the weight of the ice.

Question 23

Is radation adaptive? (experiment)

Answer 23

2 sickleback morphs set up in relevant aquaria- using growth rate as a surrogote of fitness
Results:
shows a trade of in environments, each fish does better in their own niche.
its innate not a learnt behaviour

hybrids come to be in the lab but dont work out better then their parents. (lower fitness)

Thus radation is adaptive
Has their been single or double invasion of lakes?
independent invasion and then evolution

Evolution in situ can be a great impact on diversification

Question 24

East African Cichlids (example)
adaptive diversifcation

Answer 24

Why Ecologically diverse?

Cidclid females- females choosy for colour patterns in male (sexual selection)
mouth brooders, male has egg mimics that female touches when to release sperm

environmental change
pulses of diversification

alternating periods
blue lake and green lake conditions (shallow, termid, more algae, limited light)
driven by tectonics and climate cycling (glacial and interlglacial)

Hybridisaton in green lake conditions because females can see the colour

Mutations occuring at different events

Question 25

Cyclid diversity paper lake malwe Ivory, S.J. et al. 2016. Environmental change explains cichlid adaptive radiation at Lake Malawi over the past 1.2 million years. Proccedings of the National Academy of Scicnes USA 113: 11895-11900.

Answer 25

Due to high genetic features in ecologically releavent genes Adaptive radiation where there's ecologically opportunity pulsed enviormental change sexual selection hybridisation- for selection to act upon

Question 26

Why are most species rare?

Answer 26

(globally rare) individual communities (relative abundance) communities are dominated by rare species- number of species occur relative occur at low abundance long tail of things occuring in rare species Wide spread species arent the norm

Question 27

Are there different ways to be rare? (Example Cypripedium slipper orchids)

Answer 27

Image shows distribution of genus But most species are rare Uk-Japan Cypripedium chalceolus Wide spread but if you look at countries only found in a handful of places (yorkshire) and low density- specalised limestone soil. Cypripedium subtropicum – (tibet) Narrow range endemic A raange of species in a genus thats considered rare but theres different aspects of rarity

Question 28

Point endemics

Answer 28

Endemic to single localities example: central portugal e.g. Hydraena zezerensis (bug) narrow range- one mountain, one stretch of stream and rocky cave area.

Question 29

Different ways of being rare

Answer 29

population density habitat range geographic range

Question 30

Rabinowitz’s types of rarity

Answer 30

only one way of being truly common

Question 31

Common patterns in geographical range size (how widespread things are) (gaston 2003)

Answer 31

abundance and occupancy tend to be related

Question 32

Why are most species geographically restricted? Possible mechanisms

Answer 32

Evolutionary age Relative dispersal ability Niche breadth Biogeographic accident

Question 33

evolutionary age

Answer 33

the longer a species has been around the more widespread we ecpect it to be. Learnt to deal with things adaptive radiation(more time) How to study this? phylogenic tree- see a positive relationship branch length (how long ago split off) and geogrpahical range size study- fish in north america (species life cycle) pos at start, becomes negative because species start in single populaton which expands and gets geographically bigger range- isolation events- further speciation likely hood overtime of single species becoming more restricted over time. between range size and body size for a monophyletic group of 27 North American minnow species.

Question 34

Relative dispersal ability

Answer 34

all else being equal better at getting around should be more widespread- better at colonising and higher gene flow so no splitting (maintain this one species) example- water beetle (damselfly)- wingloading capabillities geographical range vs habitat type enochrus (arribas etc al) running water species- less geographical range size (ancestrial species decided to stay in salty moving water) lentic- living in standing water- change in range size (different ancestrial standing water livers) bigger wings compared to body size in standing water species compared- geological persistance of these types of habitats (puddles dry up etc)

Question 35

paper for beetles- showing range size Rundle, S.D., Bilton, D.T., Abbott, J.C. & Foggo, A. (2007a) Range size in North American Enallagma damselflies correlates with wing size. Freshwater Biology, 52, 471-477.

Answer 35

https://www.researchgate.net/publication/224264705_Range_size_in_North_American_Enallagma_damselflies_correlates_with_wing_size

Question 36

Niche breadth

Answer 36

wider a species fundamental niche the wider spread globally they will be Specialists vs generalists generalists tend to be more wide spread looking at finches Physiological differences in setting fundamental niche breadth example- temperature in diving beetles (deronnectes) calosi et al (2010) restricted species vs widespread species temperature tolerance- widepread has double the thermal range of the others also controlled for dispersal ability (wing size) and evolutionary age (when they seperated) best predictor because thermal niche for their geographical range

Question 37

paper on niche breadth and specialists vs generalists

Answer 37

(2010) Explaining abundance–occupancy relationships in specialists and generalists: a case study on aquatic macroinvertebrates in standing waters. Journal of Animal Ecology 79: 589-601. macroinvert study showed jack of all trades master of none (2010) This positive interspecific abundance–occupancy relationship across different species is one of the most robust patterns in macroecology

Question 38

Biogeographic accident

Answer 38

where they envovled and how easy it was to expand island endemics- off the dataset their termpeature range would show that they're fairly tolerant and therefore more widespread consequence of developing in such as environment example-

Question 39

ice climate and communties (What happens in the past effects the present) Historical biogeography and present day ecology

Answer 39

image shows last few thousand years example of ice cover High latitudes were set in ice cap dramatic changes in ecological changes- glacial-interglacial cycles

Question 40

Trends in global temperature: How do we know what happened before?

Answer 40

test shells of foramenifora- single cell eukarotes with a shell- coring the ocean sediment and looking at oxygen isotpes amount by 018 vs 016 shaped by the avalability of each and how its taken up by organsims green line- overall trend in temperature whats the pattern? its got colder. Present- 3 million years much more variable in trend overall trend is cooling, increase variabiltiy not due to more data- 018- heavy isotope of oxygen- relative amounts in benthic sediments in parts per thousand

Question 41

what occured at the Paleocene–Eocene thermal maximum (PETM)?

Answer 41

a short interval of maximum temperature lasting approximately 100,000 years during the late Paleocene and early Eocene epochs (roughly 55 million years ago). Warm right up to the poles- spike in temp due to release of methane- volcanos on sea floor chucking out green house gases

Question 42

what cooled the climate after PETM? Azolla event

Answer 42

water fern sediments at high latitude- just after (PETM) find lots of remains biological feedback loop- why climate started to cool again. The huge number of azolla plants sequestered enormous quantities of atmospheric CO2 which was converted directly into azolla's biomass. As the plants died, they sank to the bottom of the Arctic Ocean where they were deposited as sediments

Question 43

What drives climate cycles?

Answer 43

changes in the earths orbit predictable series of time scales solar radiation distribution= milankovich cycles

Question 44

Milankovitch cycles

Answer 44

orbital changes effecting global climate eccentricity- how circular (more even) vs ilpitical orbit (more summer less winter )around the sun shape of elipse changes every 100k years Tilt- earths tilt releative to the sun, changes every 42k years. Greater the tilt greater seasonality Precession (wobble around axis)-change 21k years effects seasons and how similar they are in both hemispheres.

Question 45

Predicitng cooling and warming

Answer 45

earths orbit drives climate cycles

Question 46

Why does earth orbit change periodically?

Answer 46

The motion of earth and other planets- gravitaonal pull from other planets (bigger planet bigger impact)

Question 47

Why have ice ages not been present throughout earth history?

Answer 47

relative positons of continents and ocean basins and the way the arrangement of the earth effects climate situations with milankovich

Question 48

1.Role of antartica (setting the stages for ice ages)

Answer 48

isolation and setting up of antartic current, leaves it free from heat transfer. Reflects solar radiation with the build up of ice.

Question 49

2.The role of himalya and tibet

Answer 49

large area of upland above so more chance of build up of snow and ice- reflection- disrupts global air circulation, warm air masses either side of plato weathering of rocks like himalayan- deposition of carbonates takes co2 out of atmsohere and cools earth. #get paper

Question 50

3.The role of the Isthmus of Panama (closure)

Answer 50

gulf stream moves warm water north and thus more ice and snow in the arctic

Question 51

What are the consequences/ what can we still see from plestiocene ice ages?

Answer 51

1. latitudinal species gradient (extinctions at high lat) 2. Narrow range endemics are concentrated in the tropics not evenly spread out 3.communities in formerly glaciated areas assemble fairly recently (post ice)

Question 52

How could plesiocene glaciations effect diversification?

Answer 52

driven evolution for a lot of narrow range species (narrow range endemic) in places that experienced ice sheet expansion wetter and drier periods in tropic areas isolated small forest habitats therefore things could diverge from each other. Isolated by barrier (drier land etc) natural selection is different where these barriers are so things need to change allopatric speciation (barrier) example of species that survived- didnt go through intense perma frost-

Question 53

Where do species survive during these areas? endemics at low lat

Answer 53

compare china/east asia to western areas latter is much more diverse lower impact of pletsoticene climate changes in east compared to west why? easy to move from temperate zone to the tropics

Question 54

example of narrow range endemic/ temperate refugia

Answer 54

rhodadendron

Question 55

Endemics at high latitudes (us)

Answer 55

examples- eyebright, endemic to dartmoor and bodmin moor sorbus whitebeams- endemic to morcham bay seem to be restricted to areas that were under ice caps or permafrost- evolved very recently (recent origin-speciated since the ice age) 12k same with the stickle back in canadian lakes

Question 56

what is rapoports rule?

Answer 56

is an ecogeographical rule that states that latitudinal ranges of plants and animals are generally smaller at lower latitudes than at higher latitudes.

Question 57

how do we work out colonisation patterns?

Answer 57

sub fossils (patterns of colonisation) pollen that remains (polymer that makes outer grain is very resistant to weathering) population genetics (genetics of extant populations) thus reconstruct coloisation history examples- grass hoppers in different locations

Question 58

examples of post glacial newly formed communities

Answer 58

mitochondrial DNA studies on three widespread species of small mammal suggest that colonization may have occurred from glacial refugia in central Europe–western Asia. the Mediterranean peninsulae dna are distinctive from those found elsewhere. Rather than contributing to the postglacial colonization of Europe, Mediterranean populations of widespread small mammals may represent long–term isolates undergoing allopatric speciation.

Question 59

Gutjahr, M. et al. 2017. Very large release of mostly volcanic carbon during the Palaeocene–Eocene Thermal Maximum. Nature 548: 573-577. #papers Petit, R.J. et al. 2007. Glacial Refugia: Hotspots But Not Melting Pots of Genetic Diversity. Science 300: 1563-1565.

Answer 59

Glacial refuge areas are expected to harbor a large fraction of the intraspecific biodiversity of the temperate biota. To test this hypothesis, we studied chloroplast DNA variation in 22 widespread European trees and shrubs sampled in the same forests. Most species had genetically divergent populations in Mediterranean regions, especially those with low seed dispersal abilities. However, the genetically most diverse populations were not located in the south but at intermediate latitudes, a likely consequence of the admixture of divergent lineages colonizing the continent from separate refugia.

Question 60

Why do the tropics have the most species? (latitudinal diversity gradient)

Answer 60

decrease latitude in northern and southern theres an increase in species richness

Question 61

LDG

Answer 61

The pattern of having lots of species at the equator with diversity dwindling off towards the poles is known as the Latitudinal Diversity Gradient — “latitudinal” meaning how far north or south of the equator, “diversity” meaning the number of species, and “gradient” meaning the transition between high and low.

Question 62

Examples of LDG

Answer 62

ecuador vs ohio in plant species (large areas but 20k more in regional region) rapid turn over between sites

Question 63

exceptions to LDG

Answer 63

particular taxa that have specific evoultionary history (bumblebees and salamander)

Question 64

Why is there an increase in diversity towards the tropics? (LDG)

Answer 64

12 different concept methods to why its occuring- Some pos Local explanations: coexistence without exclusion Stucture of habitat in tropics (more canopy layers more species can fit- more species generally)

Question 65

Local explanations but how do species co-exist in the first place?

Answer 65

the link between local and regional richness

Question 66

What determines regional richness?

Answer 66

a balance between speciation and extinction (immigration and extinction in biogeography theory)

Question 67

What is behind lat differences in regional species richness pools?

Answer 67

is it down to productivity? more primary productivity, more food, more plants etc evapotransporation- more liquid water and solar radiation and greater intensity of both resources in the tropics (more trees example as theres more resource axis) example: bird species vs evapotransporation, positive correlation

Question 68

tropics- time cradles or museums of biodiversity?

Answer 68

museums- low extinction rates at low latitudes, over peiods of evoultionary time- why? relative environmental stability example- periods of glacial/ interglacial periods evidence- mammals decreases as decrease latitude. cradle- tropical have higher speciation rate (orgination of species happens faster-shorter generation times- consistent conditions mean things have more then 1 season to reproduce) high temp- higher background mutation rates evidence diversifcaton rates dont always correlate with latitude- angiosperms- speciation increases with latitude in this case. Could be consequence of temperate habitat opening up as cooling of the world.

Question 69

Evidence of climate stability effecting mammals evolutionary rates

Answer 69

We found an inverse relationship between evolutionary rates and species richness, especially in the terrestrial domain. Additionally, climatic instability was strongly associated with the highest evolutionary rates at high terrestrial latitudes, supporting the glacial refugia hypothesis. At low latitudes, evolutionary rates were unrelated to climatic stability

Question 70

evidence that higher speciation rates could be a factor toward LDG.

Answer 70

study on angiosperms showed that an increase in latitude brings higher specation rates

Question 71

Mannion, P.D. et al. 2014. The latitudinal biodiversity gradient through deep time. TREE 29: 42-50 (LDG is a feature of ice age conditions?)

Question 72

LDG was not always present in life history

Answer 72

tropical bands extends around the ecuator but this wasnt always the case when things were hotter LDG occured in: late permian late ordivican middle miocene

Question 73

plesitocene ice cover 3mya-today

Answer 73

much more ice extension in the northern hemisphere compared to southern. a-symmetry north vs south: its more common to have more of a drop off in north. gradient today is pear shaped- overall general ecological pattern what causes it? many explanations:

Question 74

Rex, M.A. et al. 1993. Global-scale latitudinal patterns of species diversity in the deep-sea benthos. Nature 365: 636-639.

Answer 74

report that deep-sea bivalves, gastropods and isopods show clear latitudinal diversity gradients in the North Atlantic, and strong interregional variation in the South Atlantic.

Question 75

Biodiversity and ecosystem function

Answer 75

Palm oil- cutting down original systems an implement agricultre monoculture. Diversity of these environments is different to og. What impact does this have? coral reef- lose branching corals etc during bleaching- lower arceitual complexity

Question 76

What is ecosystem function?

Answer 76

general terms- relatively broad. energy, nutrent cycling between, bio sphere, key trophic processes, consumption and how the rate changes between ecossytem. how does the rate of primary production change? when a factor is taking out? processes that underpin what goes on within ecosystem: succession- progressional change in communites over time

Question 77

ecosystem services a subset of function

Answer 77

c02 fixation, carbon sequestration etc.

Question 78

What is the relationship between ecosystem function and species richness?

Answer 78

graph- green line: proportional loss each species contributes more or less equally (as species increases the rates of ecosystem fucntion increases. Same predictable loss with extinction. High redundancy model- as the threshold is met then redundancy occurs. why? different niches are occupied but if you keep adding then niche overlap can occur. functional redundacy low redundacy- limited functunal redundacy, all species matter to lose species purple: as long as somethings there should be fine orange: more species lower the ecosystme function black dots- idosyncracy relative function doesnt fit a relationship is changing depending. Number of things doesnt matter but species identity is more important

Question 79

relationships in which ecosystem functions may be inpacted by how many species you have in the system?

Question 80

Does the number of individuals in an ecosystem effect how they work?

Question 81

idosyncracy and keystone species

Answer 81

keystone species- species which has disportunate impact on community, compared to their abundance or biomass (paine 1960's)- bigger impact then you'd expect removing one consumer: dominants- big impact with habitat structure, but high biomass. keystone species- bass, top down predation, starfish. Big impact on flow of chain.

Question 82

inter tidal community example

Answer 82

example keystone: (paine et al, 2010) inter tidal communities pisaster is eating everything in the system pretty much. Not many of them (low biomass and abundance) removing pisaster impacts and how rest of communty reacts 3 months post- barancales become more abundant 9 months- mussels start to get in and other muscles overall- 8 co-occuring sesile species vs 15 when piaster was around (muscles crowd everything else out, little algae)

Question 83

example of keystone species

Answer 83

fynbos ants, they bury seeds which then seed burial needing plants wont survive.

Question 84

how would study which relationship best applies?

Answer 84

patterns in nature compare different sites with different species and look at correlation between species richness. (confounding variables, cant account for everything or prove causation) field manipulation leaf litter bags in streams and look at rate of break down with different numbers of taxa, field vs lab, seed with different types of species in each constant environment rooms- problem hard to get conditions right for organisms (mesocosums)

Question 85

(example leaf-litter breakdown study).

Answer 85

no single model can describe all results depends on the taxa and system (idosyncracy) biodiversity does impact ecosystem function tho example study- leaf litter breakdown from shredders usually stuff that washes in lab experiment of 1, 2, 3 of stone fly species in sweden. 12 indivduals and look at rate of litter loss. across 3 species has a signifcant impact on how leaves break down. more of own species isnt as fast as different issues? what if more species would it still be the same? probelm of small scale study restricts to low biodiversity system. only one ecosystem process thus meta

Question 86

meta analysis Van der Plas, F. 2019. Biodiversity and ecosystem functioning in naturally assembled communities. Biological Reviews 94: 1220–1245

Answer 86

try to summarise decades of work all together, see overall picture. (duffy et al) (van der plaas) comparison of number of species vs functional compositon (groups) predator or consumer etc In summary, a high biodiversity in naturally assembled communities positively drives various ecosystem functions. At the same time, the strength and direction of these effects vary highly among studies, and factors other than biodiversity can be even more important in driving ecosystem functioning. Thus, to promote those ecosystem functions that underpin human well-being, conservation should not only promote biodiversity per se, but also the abiotic conditions favouring species with suitable trait combinations.

Question 87

van der plas and BEF

Answer 87

The outcomes of 258 published studies, which reported 726 BEF relationships, revealed that in many cases, biodiversity promotes average biomass production and its temporal stability, and pollination success. For decomposition rates and ecosystem multifunctionality, positive effects of biodiversity outnumbered negative effects, but neutral relationships were even more common. Similarly, negative effects of prey biodiversity on pathogen and herbivore damage outnumbered positive effects, but were less common than neutral relationships. Finally, there was no evidence that biodiversity is related to soil carbon storage.

Question 88

biogeography theory and enclosure design. workshop info

Answer 88

-power of function modle -the nymber of species on islanfs of similar habotat in the same latitiudes depeneds on the size and isolation of the islands and is balanced by the rate of extinction and immigration. -The immigration rate is supposed to decrease with increasing isolation and the extinction rate to increase with decreasing area. Thus, more distant and smaller islands are predicted to have a lower equilibrium number of species. The dynamic processes of immigration and extinction are proposed to lead to a turnover of species so that although the number of species should remain constant, the species composition should change over time. -increased environment heteogenity means less fighting for resources. -larger populations in a large area so less of a chance of local extinctions -design stategies: why? -the main reason in implementing the theory to design strateries is to stop the so-called creation of habitat 'islands' which limit the area concerned and the isolation. - a consequence is supersaturation, a new fragment will hold more species then at equillibrium. -Relaxation will ensue, with the rate of local extinction exceeding the rate of immigration, towards an equilibrium number of species. -maximising the number of species contained in a system of reserves at 1.the benefits of single large reserves as opposed to a group of small reserves; 2.arrangement of a system of reserves (3) the optimal shape of reserves. optimise dispersal distances within the reserve. Diamond (1975) suggests that if a reserve is too relationship has been used to argue that single large reserves will encompass more species than single small reserves and more than a group of small reserves of equivalent total area. The equilibrium theory has been used to argue that small reserves, once isolated in surroundings of different habitat, will lose species more rapidly and, eventually a greater total number of species, than larger reserve The ideas of species turnover and the effects of isolation on immigration and extinction, inherent in the equilibrium theory, have also been used to argue that regular, preferably circular, shaped reserves will retain more species than irregular shaped reserves elongated or has peninsulas, dispersal rates to outlying parts of the reserve from more central parts may be sufficiently low to perpetuate local extinctions by islandlike effects -