Rarity in species: definitions, sampling challenges, and causes

Rarity Learning Objectives

By the end of this session, you should be able to

• Understand the definitions of the word 'rarity'
• Describe the problems associated with sampling species
• Describe the relation between abundance and range size
• Give some causes of rarity

Species Abundance Distributions

120
136
:
100
60°
number of species
80
40
8 60
40
20
beetles from the R.Thames, England
20
M
4
8
12
16
20
24
28
32
number of individuals
4
8
12
-
16
20
24
28
32
36
40
number of individuals
What can these tell us about abundance of species ?
number of species
fresh water algae from N.E. Spain

Definitions of Rarity

Rarity can be defined in terms of:
The proportion of species:
· The rare ones in a community are those which have the lowest x%
abundance
Proportion of the total
· Add up the total number of individuals in a community and the rare
ones are those with abundance x% or less of that total
Proportion of the maximum
· Take the most common species, calculate its abundance, the
rare ones are those whose abundance is x% or less of the
common one
This could be 10%

Species Rarity Categories

Rarity: species can have
High abundance, wide range
High abundance, narrow range
8000 000
80,000
So, which are rare?
8000
800
Low abundance, wide range
Low abundance, narrow range

Vagrants and Resident Species

Vagrants : not really rare
Number of species
80
60
T
40
20
0
1-10
10-100
100-1000
Numbers of individuals
Resident, breeding
Vagrant, non-breeding
Bird survey data

Recorder Effort Impact on Rarity

Publications and Abundance

Recorder effort may impact
rarity
100
Publications
10
1
10
100
1000
10000
100000
Abundance
Publications on UK insects

Ivy Distribution in Scotland and Wales

Recorder effort II
Is ivy really rarer in parts of Scotland and Wales ?
C
268/1
HEDERA HELIX
L.
Ivy
x Recorded Intro-
ductions
. Allother records
MILET
0

Wrong Units in Ecological Density

Wrong units
Crude density
Ecological density

Species Range Distributions

Species range distributions
What range do most birds have- large or
small?
This tallies with abundance
Most species have low abundance
and low range - i.e. most species are
RARE
20
a
Non passerines
12
4 -
% of species
40 ₸
b
30
20
Passerines
10
0
40
80
120
160
Number of squares
Passerines have three toes forward, one backward, e.g. when sitting on a
perch, non-passerines don't e.g. robin
Data: African birds

Abundance Can Change

Song Thrush Populations

Abundance can change
Song thrush populations
5
L
4
Population size (millions)
2
0
1965
1970
1975
1980
1985
1990
1995
2000
RSPB reports:
of 3,148 species surveyed, 60% have declined across 50y

House Sparrows Decline

House sparrows
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It suggests sparrows are now
disappearing altogether from cities such as London, Bristol and
Edinburgh.
Dr Will Peach, from the RSPB, said many gardens had become "no-go
areas for once-common British birds".
Starving chicks
SEE ALSO
Starling tops garden birds poll
26 Mar 08 | London
'Bird-friendly' call for gardens
25 Oct 07 | UK
England's gardens 'under threat'
18 Jul 07 | England
Food scarcity is hitting sparrows
09 Feb 06 | Science & Environment
· Where is the cockney sparrow?
14 Jan 03 | England
RELATED INTERNET LINKS
RSPB
De Montfort University
Natural England
In Pictures
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Printable version
Sparrow numbers 'plummet by 68%'
The population of house
sparrows in Britain has fallen
by 68% in the past three
decades, according to the
RSPB.
A report by the charity said the
paving over of front gardens and
removal of trees had caused a big
decline in insects that the birds
eat.
SPL
The house sparrow feeds on insects
like aphids during the summer months
video and Audio
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Page last updated at 00:00 GMT, Thursday, 20 November 2008
The BBC is not responsible for the content of automnal

State of Nature Report 2023

Summary of Findings

STATE
OF
NATURE
2023
state of
nature
PARTNERSHIPSummary of findings
Terrestrial and
freshwater
19%
The abundance
of 753 terrestrial
and freshwater species
has on average fallen
by 19% across the
UK since 1970.
Within this average figure,
290 species have declined
in abundance (38%)
and 205 species have
increased (27%).
13%
The UK distributions
of 4,979 invertebrate
species have on
average decreased by
13% since 1970.
Stronger declines were
seen in some insect
groups which provide key
ecosystem functions such
as pollination (average
18% decrease in species'
distributions) and pest
control (34% decrease).
By contrast, insect groups
providing freshwater
nutrient cycling initially
declined before recovering
to above the 1970 value
(average 64% increase in
species' distributions).
54%
Since 1970, the
distributions of 54%
of flowering plant
species and 59% of
bryophytes (mosses
and liverworts) have
decreased across
Great Britain.
By comparison, only 15%
and 26% of flowering
plants and bryophytes,
respectively, have
increased. In Northern
Ireland, since 1970, 42%
of flowering plant species
and 62% of bryophytes
have decreased in
distribution, compared to
43% and 34%, respectively,
that have increased.
Turtle dove, Ben Andrew (rspb-images.
com); Forester moth, Mike Read (rspb-
images.com); Heath Spotted-Orchid,
Andy Hay (rspb-images.com); Ladybird
Spider, Ian Hughes (rspb-images.com);
Kittiwake, Ben Andrew (rspb-images.com);
Grey Seal, Ben Hall (rspb-images.com);
Atlantic Yellow Nosed Albatross,
Steffen Oppel (rspb-images.com)
16%
10,008 species were
assessed using Red List
criteria.
2% (151 species) are extinct
in Great Britain and a
further 16% (almost 1,500
species) are now threatened
with extinction here. In
Northern Ireland, 281 (12%)
of 2,508 species assessed are
threatened with extinction
from the island of Ireland.
Marine
24%
The abundance of 13
species of seabird has
fallen by an average of
24% since 1986.
The situation is worse
in Scotland, where the
abundance of 11 seabird
species has fallen by an
average of 49% since 1986.
These results pre-date the
potentially major impact
of the ongoing outbreak of
Highly Pathogenic Avian
Influenza.
Varied picture for other
marine life.
We know less about
changes in species
abundance and
distribution in UK seas.
Well-monitored species of
demersal fish (those living
on or near the seafloor, 105
species) showed an average
increase in abundance
during the 1990s and
early 2000s but have since
declined. Whales and
dolphins (three species)
have shown little change
in average abundance
since the early 1990s.
Grey Seal abundance has
increased as they recover
from historical hunting
pressure. Harbour Seals
are in decline in parts of
north-east Scotland and
south-east England, but
are stable or increasing in
other regions.
UKOT and CDs
UK Overseas Territories
and Crown
Dependencies.
94% of the species unique
to the UK and its territories
are found on the Overseas
Territories. Across the
Overseas Territories and
Crown Dependencies, 11%
of 6,557 species assessed
are threatened with global
extinction.
Black Guillemot,
Ben Andrew (mpb-images.com)
What do our
headlines mean?
This report focuses on three measures
of biodiversity change: abundance
(the number of individuals), distribution
(the proportion of sites occupied) and
extinction risk. These measures have
been assessed for hundreds and in some
cases thousands of species native to the
UK, as the available data allow.
Our results show:
· The number of species that have
increased or decreased in abundance
or distribution over time
· The average change in abundance or
distribution across species over time
· The proportion of species at risk of
being lost from the country.
Here we present UK findings in most
cases. Where UK information is not
available, we present results for
Great Britain and Northern Ireland
separately.
4
5

Relationship Between Abundance and Range Size

Relationship between abundance and
range size
Gives a 'sky at night effect'
+
C
Log. density
Some have
high
abundance
and high
range
:
0
Some have
low
abundance
and low
range
0
Log. range size

British and European Birds: Local and Regional Range

British and European birds-
local and regional range
10000000
1000000
European
100000
10000
1000
100
100
1000
10000
100000
1000000
British and Irish
Suggests
there is a
link
between
local and
regional
abundance

Abundance Changes Quickly

Abundance can change quickly
1974
1975
1
1976
1977
Elder aphid
populations

Rules for Community Assemblages

There are rules for community
assemblages
Freshwater streams 1985 and 1986
Researchers visited streams,
recorded abundance, then
killed everything
Went back the next year
and measured species that
had recolonised
The abundance in 1986
related to the abundance
the year before
1000
N+1 (1986)
100
10
1
1
10
100
1000
N+1 (1985)

Range Size and Population

Theoretical changes in population size as range changes
a) Any reduction in range size results in extinction
b)Linear decline
c) Any reduction in range size has a large effect
on the population but then it takes a long time
for the the last few to go
d) Can cope with a reasonable reduction in
range size before there is a significant
effect on the population
a
b
C
Population size
d
Range size

Why Are Species Rare?

Specialised Diets

Why are species rare?
Specialised diets
160
Mean range size of polyphages
(within genera)
x
140
x
120
100 -
×
x
*
×
X
80
x
X
x
x
60
x
40
x
20
×
X
0
0
20
40
60
80
100
120
140
160
Mean range size of monophages (within genera)
The line is y=x
The majority of crosses appear
above the line
So mean range size of the
monophages is less than the
polyphages in the same genus
So species with a broad diet
tend to be more common than
species with a narrow diet
Monophages
have a smaller
range than
polyphages
x
×
X

Dispersal Ability in Plants

Dispersal ability
For plants
e.g dog's mercury v dandelion
Species with no dispersal
80
% of species
60
40
20
0
Increasing
Decreasing
Species with good dispersal
80
% of species
60
응 40
20
-
0
Increasing
Decreasing
British flora

Other Reasons for Rarity

Other reasons
Niche availability
Interspecific competition
Predator pressure
** Human influences
Climate effects
Random chance
Body size

Rarity Learning Objectives Review

Learning objectives
By the end of this session, you should be able to:
Understand the definitions of the word 'rarity'
❖
Describe the problems associated with sampling species
❖
Describe the relation between abundance and range size
❖
Give some causes of rarity